FFmpeg

https://ffmpeg.org/doxygen/7.0
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### Setup DVD Chapters with Pre-indexing

Source: https://ffmpeg.org/doxygen/7.0/dvdvideodec_8c_source.html

Initiates the setup for DVD chapters using pre-indexing. This process can be time-consuming and involves opening the playback state and iterating through navigation blocks to identify chapter markers. Logs an informational message indicating the start of this process.

```c
av_log(s, AV_LOG_INFO,
"Indexing chapter markers, this will take a long time. Please wait...\n");

while (!(interrupt = ff_check_interrupt(&s->interrupt_callback))) {
```

--------------------------------

### Get GUID as String

Source: https://ffmpeg.org/doxygen/7.0/mf__utils_8c_source.html

Macro to get the string representation of a GUID. This is a shorthand for ff_guid_str_buf.

```c
#define ff_guid_str(guid)
```

--------------------------------

### setup_window

Source: https://ffmpeg.org/doxygen/7.0/xcbgrab_8c.html

Sets up the XCB window for grabbing.

```APIDOC
## setup_window()

### Description
Configures and prepares the XCB window for screen grabbing operations.

### Parameters
- **_s_** (AVFormatContext *) - Pointer to the AVFormatContext.

### Return Value
None.
```

--------------------------------

### W64 Muxer: Start GUID

Source: https://ffmpeg.org/doxygen/7.0/wavenc_8c_source.html

Writes a GUID and a 64-bit length value to the AVIOContext, marking the start of a chunk. This is used in the W64 format for defining sections like 'fmt' and 'data'.

```c
static void start_guid(AVIOContext *pb, const uint8_t *guid, int64_t *pos)
{
    *pos = avio_tell(pb);

    avio_write(pb, guid, 16);
    avio_wl64(pb, INT64_MAX);
}
```

--------------------------------

### Main Program Entry Point

Source: https://ffmpeg.org/doxygen/7.0/rotozoom_8c_source.html

Sets up the video stream generation process. Parses command-line arguments, initializes demo resources, and generates a sequence of frames, saving them to a file or directory.

```c
int main(int argc, char **argv)
{
int w, h, i;
char buf[1024];
int isdir = 0;

if (argc != 3) {
printf("usage: %s image.pnm file|dir\n" 
"generate a test video stream\n", argv[0]);
return 1;
}

if (!freopen(argv[2], "wb", stdout))
isdir = 1;

w = DEFAULT_WIDTH;
h = DEFAULT_HEIGHT;

rgb_tab = malloc(w * h * 3);
wrap = w * 3;
width = w;
height = h;

if (init_demo(argv[1]))
return 1;

for (i = 0; i < DEFAULT_NB_PICT; i++) {
gen_image(i, w, h);
if (isdir) {
snprintf(buf, sizeof(buf), "%s%02d.pgm", argv[2], i);
pgmyuv_save(buf, w, h, rgb_tab);
} else {
pgmyuv_save(NULL, w, h, rgb_tab);
}
}

free(rgb_tab);
return 0;
}
```

--------------------------------

### Get GUID Function

Source: https://ffmpeg.org/doxygen/7.0/asfdec__o_8c_source.html

Reads a Globally Unique Identifier (GUID) from an AVIOContext. This is common in file format parsing.

```c
int ff_get_guid(AVIOContext *s, ff_asf_guid *g)
```

--------------------------------

### main()

Source: https://ffmpeg.org/doxygen/7.0/qt-faststart_8c.html

The main entry point of the qt-faststart utility. It processes command-line arguments and orchestrates the MP4 file optimization.

```APIDOC
## main()

### Description
Main function for the qt-faststart utility. Handles command-line arguments and MP4 file processing.

### Parameters
- `_argc_` (int) - The number of command-line arguments.
- `_argv_[]` (char *) - An array of strings representing the command-line arguments.

### Return Value
An integer exit code (0 for success, non-zero for failure).
```

--------------------------------

### Main Function: Initialization and Setup

Source: https://ffmpeg.org/doxygen/7.0/enc__recon__frame__test_8c_source.html

Initializes the program, parses command-line arguments for input file, encoder name, encoder options, and optional frame count, thread count, and thread type. It then finds and allocates the encoder and decoder contexts.

```c
int main(int argc, char **argv)
{
PrivData pd;
DecodeContext dc;

const char *filename, *enc_name, *enc_opts, *thread_type = NULL, *nb_threads = NULL;
const AVCodec *enc, *dec;
int ret = 0, max_frames = 0;

if (argc < 4) {
fprintf(stderr,
"Usage: %s <input file> <encoder> <encoder options> "
"[<max frame count> [<thread count> <thread type>]\n",
argv[0]);
return 0;
}

filename = argv[1];
enc_name = argv[2];
enc_opts = argv[3];
if (argc >= 5)
max_frames = strtol(argv[4], NULL, 0);
if (argc >= 6)
nb_threads = argv[5];
if (argc >= 7)
thread_type = argv[6];

memset(&dc, 0, sizeof(dc));
memset(&pd, 0, sizeof(pd));

enc = avcodec_find_encoder_by_name(enc_name);
if (!enc) {
fprintf(stderr, "No such encoder: %s\n", enc_name);
return 1;
}
if (!(enc->capabilities & AV_CODEC_CAP_ENCODER_RECON_FRAME)) {
fprintf(stderr, "Encoder '%s' cannot output reconstructed frames\n",
enc->name);
return 1;
}

dec = avcodec_find_decoder(enc->id);
if (!dec) {
fprintf(stderr, "No decoder for: %s\n", avcodec_get_name(enc->id));
return 1;
}


```

--------------------------------

### Get Codec ID from GUID Array

Source: https://ffmpeg.org/doxygen/7.0/riffdec_8c_source.html

Identifies an audio codec ID by comparing a given GUID against an array of known codec GUIDs. Returns AV_CODEC_ID_NONE if no match is found.

```c
enum AVCodecID ff_codec_guid_get_id(const AVCodecGuid *guids, ff_asf_guid guid)
{
    int i;
    for (i = 0; guids[i].id != AV_CODEC_ID_NONE; i++)
        if (!ff_guidcmp(guids[i].guid, guid))
            return guids[i].id;
    return AV_CODEC_ID_NONE;
}
```

--------------------------------

### Get Start Offset for Macroblock

Source: https://ffmpeg.org/doxygen/7.0/rv34_8c_source.html

Determines the starting bitstream offset for a macroblock based on its size. This function is intended to be potentially replaced by `ff_h263_decode_mba()`.

```c
int ff_rv34_get_start_offset(GetBitContext *gb, int mb_size)
{
    int i;
    for(i = 0; i < 5; i++)
        if(rv34_mb_max_sizes[i] >= mb_size - 1)
            break;
    return rv34_mb_bits_sizes[i];
}
```

--------------------------------

### setup_window

Source: https://ffmpeg.org/doxygen/7.0/globals_func_s.html

Sets up a window for screen capture. Used in xcbgrab.c.

```APIDOC
## setup_window

### Description
Sets up a window for screen capture.

### Files
xcbgrab.c
```

--------------------------------

### setup_partitions

Source: https://ffmpeg.org/doxygen/7.0/vp8_8c.html

Sets up partitions for VP8 decoding.

```APIDOC
## setup_partitions()

### Description
Sets up partitions for VP8 decoding.

### Signature
`static int setup_partitions(VP8Context *_s_, const uint8_t *_buf_, int _buf_size_)
`
```

--------------------------------

### NVDEC H.264 Start Frame Function

Source: https://ffmpeg.org/doxygen/7.0/nvdec__h264_8c_source.html

Handles the start of frame processing for H.264 decoding with NVDEC. This function is part of the hardware acceleration setup.

```c
static int nvdec_h264_start_frame(AVCodecContext *avctx, const uint8_t *buffer, uint32_t size)
{
    // Placeholder for actual frame start logic
    // In a real implementation, this would prepare for decoding a new frame.
    // For example, it might reset frame-specific data or allocate buffers.
    // The provided snippet is minimal and likely part of a larger structure.
    // pp->intra_pic_flag = 0; // Example of setting a frame property
    return 0;
}
```

--------------------------------

### Main Function Example

Source: https://ffmpeg.org/doxygen/7.0/tests_2celp__math_8c_source.html

Demonstrates the usage of ff_dot_productf, ff_dot_product, ff_log2_q15, and av_assert0 within a main function.

```c
int main(void)
{
    int i;
    const float f1[3] = {0.0, 1.1, 2.2};
    const float f2[3] = {3.3, 4.4, 5.5};
    const int16_t i1[3] = {6, 7, 8};
    const int16_t i2[3] = {9, 10, 11};

    float r = ff_dot_productf(f1, f2, FF_ARRAY_ELEMS(f1));
    int64_t d = ff_dot_product(i1, i2, FF_ARRAY_ELEMS(i1));

    IsAlmostEqual(16.94f, r, 0.000001f);
    av_assert0(212 == d);

    for (i = 1024; i >= 1; i/=2)
        av_assert0(ff_log2_q15(i) == (1<<15)*((int)log2(i))+(1<<2));

    return 0;
 }
```

--------------------------------

### Get RV34 Slice Start Offset

Source: https://ffmpeg.org/doxygen/7.0/rv30_8c_source.html

Calculates and returns the starting offset for a slice in the RV34 bitstream. This is crucial for correctly parsing slice data.

```c
int ff_rv34_get_start_offset(GetBitContext *gb, int mb_size)
{
Decode starting slice position.

```

--------------------------------

### ff_opencl_get_event_time

Source: https://ffmpeg.org/doxygen/7.0/opencl_8c.html

Gets the command start and end times for a given OpenCL event.

```APIDOC
## ff_opencl_get_event_time()

### Description
Gets the command start and end times for the given event and returns the difference (the time that the event took).

### Parameters
- **event** (cl_event) - The OpenCL event.

### Return Value
- **cl_ulong** - The time difference in nanoseconds.
```

--------------------------------

### setup_partitions

Source: https://ffmpeg.org/doxygen/7.0/globals_func_s.html

Sets up partitioning for encoding. Used in vp8.c.

```APIDOC
## setup_partitions

### Description
Sets up partitioning for encoding.

### Files
vp8.c
```

--------------------------------

### FFmpeg Thread Finish Setup Function

Source: https://ffmpeg.org/doxygen/7.0/mpeg12dec_8c_source.html

Completes thread setup for decoding. Ensures that AVFrame fields like pkt_dts and pkt_pts are correctly set. Call this after decoding starts and before it finishes.

```c
ff_thread_finish_setup
```

--------------------------------

### Main Function Setup

Source: https://ffmpeg.org/doxygen/7.0/avio_read_callback_8c-example.html

Initializes the AVIOContext with a custom read callback and buffer data. This setup is crucial for FFmpeg to read from a custom data source.

```c
int main(int argc, char *argv[])
{
    AVIOContext *ctx = NULL;
    buffer_data bd = {0};
    uint8_t *buffer = NULL;
    int ret = 0;

    // ... (buffer allocation and initialization) ...

    ctx = avio_alloc_context(buffer, bd.size, 0, &bd, read_packet, NULL, NULL);
    if (!ctx) {
        av_log(NULL, AV_LOG_FATAL, "Could not allocate AVIOContext\n");
        ret = AVERROR(ENOMEM);
        goto end;
    }

    // ... (further processing with ctx) ...

end:
    if (ctx && !(ctx->flags & AVIO_FLAG_NONBLOCK))
        avio_context_free(&ctx);
    else if (ctx)
        buffer[AVIO_MAX_READ_SIZE-1] = 0;

    return ret;
}
```

--------------------------------

### QSV H.264 Decoding Setup and Execution

Source: https://ffmpeg.org/doxygen/7.0/qsv_decode_8c-example.html

This C code demonstrates the full process of QSV-accelerated H.264 decoding. It includes opening input files, initializing the QSV device and H.264 decoder, reading and decoding packets, transferring decoded frames to system memory, and writing them to an output file. Ensure the QSV decoder is available in your libavcodec build.

```c
#include <stdio.h>
#include "libavformat/avformat.h"
#include "libavformat/avio.h"
#include "libavcodec/avcodec.h"
#include "libavutil/buffer.h"
#include "libavutil/error.h"
#include "libavutil/hwcontext.h"
#include "libavutil/hwcontext_qsv.h"
#include "libavutil/mem.h"
static int get_format(AVCodecContext *avctx, const enum AVPixelFormat *pix_fmts)
{
while (*pix_fmts != AV_PIX_FMT_NONE) {
if (*pix_fmts == AV_PIX_FMT_QSV) {
return AV_PIX_FMT_QSV;
}
pix_fmts++;
}
fprintf(stderr, "The QSV pixel format not offered in get_format()\n");
return AV_PIX_FMT_NONE;
}
static int decode_packet(AVCodecContext *decoder_ctx,
AVFrame *frame, AVFrame *sw_frame,
AVPacket *pkt, AVIOContext *output_ctx)
{
int ret = 0;
ret = avcodec_send_packet(decoder_ctx, pkt);
if (ret < 0) {
fprintf(stderr, "Error during decoding\n");
return ret;
}
while (ret >= 0) {
int i, j;
ret = avcodec_receive_frame(decoder_ctx, frame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
break;
else if (ret < 0) {
fprintf(stderr, "Error during decoding\n");
return ret;
}
/* A real program would do something useful with the decoded frame here.
* We just retrieve the raw data and write it to a file, which is rather
* useless but pedagogic. */
ret = av_hwframe_transfer_data(sw_frame, frame, 0);
if (ret < 0) {
fprintf(stderr, "Error transferring the data to system memory\n");
goto fail;
}
for (i = 0; i < FF_ARRAY_ELEMS(sw_frame->data) && sw_frame->data[i]; i++)
for (j = 0; j < (sw_frame->height >> (i > 0)); j++)
avio_write(output_ctx, sw_frame->data[i] + j * sw_frame->linesize[i], sw_frame->width);
fail:
av_frame_unref(sw_frame);
av_frame_unref(frame);
if (ret < 0)
return ret;
}
return 0;
}
int main(int argc, char **argv)
{
AVFormatContext *input_ctx = NULL;
AVStream *video_st = NULL;
AVCodecContext *decoder_ctx = NULL;
const AVCodec *decoder;
AVPacket *pkt = NULL;
AVFrame *frame = NULL, *sw_frame = NULL;
AVIOContext *output_ctx = NULL;
int ret, i;
AVBufferRef *device_ref = NULL;
if (argc < 3) {
fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
return 1;
}
/* open the input file */
ret = avformat_open_input(&input_ctx, argv[1], NULL, NULL);
if (ret < 0) {
fprintf(stderr, "Cannot open input file '%s': ", argv[1]);
goto finish;
}
/* find the first H.264 video stream */
for (i = 0; i < input_ctx->nb_streams; i++) {
AVStream *st = input_ctx->streams[i];
if (st->codecpar->codec_id == AV_CODEC_ID_H264 && !video_st)
video_st = st;
else
st->discard = AVDISCARD_ALL;
}
if (!video_st) {
fprintf(stderr, "No H.264 video stream in the input file\n");
goto finish;
}
/* open the hardware device */
ret = av_hwdevice_ctx_create(&device_ref, AV_HWDEVICE_TYPE_QSV,
"auto", NULL, 0);
if (ret < 0) {
fprintf(stderr, "Cannot open the hardware device\n");
goto finish;
}
/* initialize the decoder */
decoder = avcodec_find_decoder_by_name("h264_qsv");
if (!decoder) {
fprintf(stderr, "The QSV decoder is not present in libavcodec\n");
goto finish;
}
decoder_ctx = avcodec_alloc_context3(decoder);
if (!decoder_ctx) {
ret = AVERROR(ENOMEM);
goto finish;
}
decoder_ctx->codec_id = AV_CODEC_ID_H264;
if (video_st->codecpar->extradata_size) {
decoder_ctx->extradata = av_mallocz(video_st->codecpar->extradata_size +
AV_INPUT_BUFFER_PADDING_SIZE);
if (!decoder_ctx->extradata) {
ret = AVERROR(ENOMEM);
goto finish;
}
memcpy(decoder_ctx->extradata, video_st->codecpar->extradata,
video_st->codecpar->extradata_size);
decoder_ctx->extradata_size = video_st->codecpar->extradata_size;
}
decoder_ctx->hw_device_ctx = av_buffer_ref(device_ref);
decoder_ctx->get_format = get_format;
ret = avcodec_open2(decoder_ctx, NULL, NULL);
if (ret < 0) {
fprintf(stderr, "Error opening the decoder: ");
goto finish;
}
/* open the output stream */
ret = avio_open(&output_ctx, argv[2], AVIO_FLAG_WRITE);
if (ret < 0) {
fprintf(stderr, "Error opening the output context: ");
goto finish;
}
frame = av_frame_alloc();
sw_frame = av_frame_alloc();
pkt = av_packet_alloc();
if (!frame || !sw_frame || !pkt) {
ret = AVERROR(ENOMEM);
goto finish;
}
/* actual decoding */
while (ret >= 0) {
ret = av_read_frame(input_ctx, pkt);
if (ret < 0)
break;
if (pkt->stream_index == video_st->index)
ret = decode_packet(decoder_ctx, frame, sw_frame, pkt, output_ctx);
av_packet_unref(pkt);
}
/* flush the decoder */
ret = decode_packet(decoder_ctx, frame, sw_frame, NULL, output_ctx);
finish:
if (ret < 0) {
char buf[1024];
av_strerror(ret, buf, sizeof(buf));
fprintf(stderr, "%s\n", buf);
}
avformat_close_input(&input_ctx);
av_frame_free(&frame);
av_frame_free(&sw_frame);
av_packet_free(&pkt);
avcodec_free_context(&decoder_ctx);
av_buffer_unref(&device_ref);
avio_close(output_ctx);
return ret;
}
```

--------------------------------

### VC1 DXVA2 Start Frame Function

Source: https://ffmpeg.org/doxygen/7.0/dxva2__vc1_8c_source.html

Initializes the start of a frame for VC1 decoding using DXVA2. This function is part of the hardware acceleration setup and is called before processing frame data.

```c
static int dxva2_vc1_start_frame(AVCodecContext *avctx, av_unused const uint8_t *buffer, av_unused uint32_t size)
{
    return 0;
}
```

--------------------------------

### Get Relative Time in Microseconds

Source: https://ffmpeg.org/doxygen/7.0/time_8c_source.html

Gets the current time in microseconds since an unspecified starting point. It prefers `CLOCK_MONOTONIC` if available, otherwise falls back to `av_gettime` with an added offset.

```c
#include "time.h"
#include "error.h"

int64_t av_gettime_relative(void)
{
#if HAVE_CLOCK_GETTIME && defined(CLOCK_MONOTONIC)
#ifdef __APPLE__
    if (&clock_gettime)
#endif
    {
        struct timespec ts;
        clock_gettime(CLOCK_MONOTONIC, &ts);
        return (int64_t)ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
    }
#endif
    return av_gettime() + 42 * 60 * 60 * INT64_C(1000000);
}
```

--------------------------------

### setup_mb_info

Source: https://ffmpeg.org/doxygen/7.0/globals_func_s.html

Sets up macroblock information. Used in libx264.c.

```APIDOC
## setup_mb_info

### Description
Sets up macroblock information.

### Files
libx264.c
```

--------------------------------

### Get Video Configuration

Source: https://ffmpeg.org/doxygen/7.0/avfoundation_8m_source.html

Retrieves and applies the video configuration settings after the capture session is started.

```objective-c
if (video_device && get_video_config(s)) {
    goto fail;
}
```

--------------------------------

### Main Function for HW Decoding Example

Source: https://ffmpeg.org/doxygen/7.0/hw_decode_8c-example.html

Sets up and runs the hardware-accelerated decoding process. It parses command-line arguments for device type, input, and output files, finds the video stream, configures the decoder, and initializes the hardware context.

```c
int main(int argc, char *argv[])
{
    AVFormatContext *input_ctx = NULL;
    int video_stream, ret;
    AVStream *video = NULL;
    AVCodecContext *decoder_ctx = NULL;
    const AVCodec *decoder = NULL;
    AVPacket *packet = NULL;
    enum AVHWDeviceType type;
    int i;
    if (argc < 4) {
        fprintf(stderr, "Usage: %s <device type> <input file> <output file>\n", argv[0]);
        return -1;
    }
    type = av_hwdevice_find_type_by_name(argv[1]);
    if (type == AV_HWDEVICE_TYPE_NONE) {
        fprintf(stderr, "Device type %s is not supported.\n", argv[1]);
        fprintf(stderr, "Available device types:");
        while((type = av_hwdevice_iterate_types(type)) != AV_HWDEVICE_TYPE_NONE)
            fprintf(stderr, " %s", av_hwdevice_get_type_name(type));
        fprintf(stderr, "\n");
        return -1;
    }
    packet = av_packet_alloc();
    if (!packet) {
        fprintf(stderr, "Failed to allocate AVPacket\n");
        return -1;
    }
    /* open the input file */
    if (avformat_open_input(&input_ctx, argv[2], NULL, NULL) != 0) {
        fprintf(stderr, "Cannot open input file '%s'\n", argv[2]);
        return -1;
    }
    if (avformat_find_stream_info(input_ctx, NULL) < 0) {
        fprintf(stderr, "Cannot find input stream information.\n");
        return -1;
    }
    /* find the video stream information */
    ret = av_find_best_stream(input_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &decoder, 0);
    if (ret < 0) {
        fprintf(stderr, "Cannot find a video stream in the input file\n");
        return -1;
    }
    video_stream = ret;
    for (i = 0;;
 i++) {
        const AVCodecHWConfig *config = avcodec_get_hw_config(decoder, i);
        if (!config) {
            fprintf(stderr, "Decoder %s does not support device type %s.\n",
                    decoder->name, av_hwdevice_get_type_name(type));
            return -1;
        }
        if (config->methods & AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX &&
            config->device_type == type) {
            hw_pix_fmt = config->pix_fmt;
            break;
        }
    }
    if (!(decoder_ctx = avcodec_alloc_context3(decoder)))
        return AVERROR(ENOMEM);
    video = input_ctx->streams[video_stream];
    if (avcodec_parameters_to_context(decoder_ctx, video->codecpar) < 0)
        return -1;
    decoder_ctx->get_format = get_hw_format;
    if (hw_decoder_init(decoder_ctx, type) < 0)
        return -1;
    if ((ret = avcodec_open2(decoder_ctx, decoder, NULL)) < 0) {
        fprintf(stderr, "Failed to open codec for stream #%u\n", video_stream);
        return -1;
    }
    return 0;
}
```

--------------------------------

### vaapi_encode_h265_init

Source: https://ffmpeg.org/doxygen/7.0/vaapi__encode__h265_8c.html

Initializes the VAAPI H.265 encoder. This function performs the necessary setup to start the encoding process.

```APIDOC
## vaapi_encode_h265_init()

### Description
Initializes the VAAPI H.265 encoder.

### Parameters
- `_avctx_` (AVCodecContext *): Pointer to the AVCodecContext.

### Return Value
Returns an integer status code.
```

--------------------------------

### Main Function Entry Point

Source: https://ffmpeg.org/doxygen/7.0/vaapi__transcode_8c_source.html

Parses command-line arguments, initializes the VAAPI device, opens the input file, finds the specified encoder, and sets up the output context.

```c
int main(int argc, char **argv)
{
    const AVCodec *enc_codec;
    int ret = 0;
    AVPacket *dec_pkt;

    if (argc != 4) {
        fprintf(stderr, "Usage: %s <input file> <encode codec> <output file>\n"
                "The output format is guessed according to the file extension.\n"
                "\n", argv[0]);
        return -1;
    }

    ret = av_hwdevice_ctx_create(&hw_device_ctx, AV_HWDEVICE_TYPE_VAAPI, NULL, NULL, 0);
    if (ret < 0) {
        fprintf(stderr, "Failed to create a VAAPI device. Error code: %s\n", av_err2str(ret));
        return -1;
    }

    dec_pkt = av_packet_alloc();
    if (!dec_pkt) {
        fprintf(stderr, "Failed to allocate decode packet\n");
        goto end;
    }

    if ((ret = open_input_file(argv[1])) < 0)
        goto end;

    if (!(enc_codec = avcodec_find_encoder_by_name(argv[2]))) {
        fprintf(stderr, "Could not find encoder '%s'\n", argv[2]);
        ret = -1;
        goto end;
    }

    if ((ret = (avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, argv[3]))) < 0) {
        fprintf(stderr, "Failed to deduce output format from file extension. Error code: "
                "%s\n", av_err2str(ret));
        goto end;
    }

    if (!(encoder_ctx = avcodec_alloc_context3(enc_codec))) {
        ret = AVERROR(ENOMEM);
        goto end;
    }

    ret = avio_open(&ofmt_ctx->pb, argv[3], AVIO_FLAG_WRITE);
    if (ret < 0) {
        fprintf(stderr, "Cannot open output file. "
                "Error code: %s\n", av_err2str(ret));
        goto end;
    }

    /* ... transcoding loop ... */

end:
    avformat_close_input(&ifmt_ctx);
    avformat_close_input(&ofmt_ctx);
    avcodec_free_context(&decoder_ctx);
    avcodec_free_context(&encoder_ctx);
    av_buffer_unref(&hw_device_ctx);
    av_packet_free(&dec_pkt);
    return ret;
}
```

--------------------------------

### Get Compatible DXVA Decoder GUID

Source: https://ffmpeg.org/doxygen/7.0/dxva2_8c_source.html

Finds a suitable DXVA decoder GUID for the given codec context and surface format. It iterates through available DXVA modes, checks compatibility, and validates the output format using D3D11VA or DXVA2 functions. Logs supported GUIDs for debugging.

```c
static int dxva_get_decoder_guid(AVCodecContext *avctx, void *service, void *surface_format,
unsigned guid_count, const GUID *guid_list, GUID *decoder_guid)
{
FFDXVASharedContext *sctx = DXVA_SHARED_CONTEXT(avctx);
unsigned i, j;

dxva_list_guids_debug(avctx, service, guid_count, guid_list);

*decoder_guid = ff_GUID_NULL;
for (i = 0; dxva_modes[i].guid; i++) {
const dxva_mode *mode = &dxva_modes[i];
int validate;
if (!dxva_check_codec_compatibility(avctx, mode))
continue;

for (j = 0; j < guid_count; j++) {
if (IsEqualGUID(mode->guid, &guid_list[j]))
break;
}
if (j == guid_count)
continue;

#if CONFIG_D3D11VA
if (sctx->pix_fmt == AV_PIX_FMT_D3D11)
validate = d3d11va_validate_output(service, *mode->guid, surface_format);
#endif
#if CONFIG_DXVA2
if (sctx->pix_fmt == AV_PIX_FMT_DXVA2_VLD)
validate = dxva2_validate_output(service, *mode->guid, surface_format);
#endif
if (validate) {
*decoder_guid = *mode->guid;
break;
}
}

if (IsEqualGUID(decoder_guid, &ff_GUID_NULL)) {
av_log(avctx, AV_LOG_VERBOSE, "No decoder device for codec found\n");
return AVERROR(EINVAL);
}

if (IsEqualGUID(decoder_guid, &ff_DXVADDI_Intel_ModeH264_E))
    sctx->workaround |= FF_DXVA2_WORKAROUND_INTEL_CLEARVIDEO;

return 0;
```

--------------------------------

### QSV Transcoding Usage Example

Source: https://ffmpeg.org/doxygen/7.0/qsv_transcode_8c-example.html

Illustrates the command-line usage for the QSV transcoding example. It shows how to specify input/output files, codec, initial encoder options, and dynamic option changes with frame numbers.

```bash
# qsv_transcode input.mp4 h264_qsv output_h264.mp4 "g 60"
# qsv_transcode input.mp4 hevc_qsv output_hevc.mp4 "g 60 async_depth 1"
# 100 "g 120"
```

--------------------------------

### Setup RTSP HTTP Tunneling (GET Request)

Source: https://ffmpeg.org/doxygen/7.0/rtsp_8c_source.html

Initializes the RTSP tunneling mechanism by allocating and connecting an FFurl context for GET requests. Sets up necessary headers including a session cookie and accept type.

```c
/* set up initial handshake for tunneling */
char httpname[1024];
char sessioncookie[17];
char headers[1024];
AVDictionary *options = NULL;

av_dict_set_int(&options, "timeout", rt->stimeout, 0);

ff_url_join(httpname, sizeof(httpname), https_tunnel ? "https" : "http", auth, host, port, "%s", path);
snprintf(sessioncookie, sizeof(sessioncookie), "%08x%08x",
            av_get_random_seed(), av_get_random_seed());

/* GET requests */
if (ffurl_alloc(&rt->rtsp_hd, httpname, AVIO_FLAG_READ,
                &s->interrupt_callback) < 0) {
    err = AVERROR(EIO);
    goto fail;
}

/* generate GET headers */
snprintf(headers, sizeof(headers),
        "x-sessioncookie: %s\r\n"
        "Accept: application/x-rtsp-tunnelled\r\n"
        "Pragma: no-cache\r\n"
        "Cache-Control: no-cache\r\n",
        sessioncookie);
av_opt_set(rt->rtsp_hd->priv_data, "headers", headers, 0);

if (!rt->rtsp_hd->protocol_whitelist && s->protocol_whitelist) {
    rt->rtsp_hd->protocol_whitelist = av_strdup(s->protocol_whitelist);
    if (!rt->rtsp_hd->protocol_whitelist) {
        err = AVERROR(ENOMEM);
        goto fail;
    }
}

/* complete the connection */
if (ffurl_connect(rt->rtsp_hd, &options)) {
    av_dict_free(&options);
    err = AVERROR(EIO);
    goto fail;
}
```

--------------------------------

### Main function for Video Encoding Example

Source: https://ffmpeg.org/doxygen/7.0/encode__video_8c_source.html

Sets up the video encoding process, including finding a codec, allocating context, setting parameters, opening the codec, and preparing frames. It then iterates to encode frames and flushes the encoder at the end.

```c
int main(int argc, char **argv)
{
    const char *filename, *codec_name;
    const AVCodec *codec;
    AVCodecContext *c= NULL;
    int i, ret, x, y;
    FILE *f;
    AVFrame *frame;
    AVPacket *pkt;
    uint8_t endcode[] = { 0, 0, 1, 0xb7 };

    if (argc <= 2) {
        fprintf(stderr, "Usage: %s <output file> <codec name>\n", argv[0]);
        exit(0);
    }
    filename = argv[1];
    codec_name = argv[2];

    /* find the mpeg1video encoder */
    codec = avcodec_find_encoder_by_name(codec_name);
    if (!codec) {
        fprintf(stderr, "Codec '%s' not found\n", codec_name);
        exit(1);
    }

    c = avcodec_alloc_context3(codec);
    if (!c) {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(1);
    }

    pkt = av_packet_alloc();
    if (!pkt)
        exit(1);

    /* put sample parameters */
    c->bit_rate = 400000;
    /* resolution must be a multiple of two */
    c->width = 352;
    c->height = 288;
    /* frames per second */
    c->time_base = (AVRational){1, 25};
    c->framerate = (AVRational){25, 1};

    /* emit one intra frame every ten frames
     * check frame pict_type before passing frame
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
     * then gop_size is ignored and the output of encoder
     * will always be I frame irrespective to gop_size
     */
    c->gop_size = 10;
    c->max_b_frames = 1;
    c->pix_fmt = AV_PIX_FMT_YUV420P;

    if (codec->id == AV_CODEC_ID_H264)
        av_opt_set(c->priv_data, "preset", "slow", 0);

    /* open it */
    ret = avcodec_open2(c, codec, NULL);
    if (ret < 0) {
        fprintf(stderr, "Could not open codec: %s\n", av_err2str(ret));
        exit(1);
    }

    f = fopen(filename, "wb");
    if (!f) {
        fprintf(stderr, "Could not open %s\n", filename);
        exit(1);
    }

    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate video frame\n");
        exit(1);
    }
    frame->format = c->pix_fmt;
    frame->width = c->width;
    frame->height = c->height;

    ret = av_frame_get_buffer(frame, 0);
    if (ret < 0) {
        fprintf(stderr, "Could not allocate the video frame data\n");
        exit(1);
    }

    /* encode 1 second of video */
    for (i = 0; i < 25; i++) {
        fflush(stdout);

        /* Make sure the frame data is writable.
         * On the first round, the frame is fresh from av_frame_get_buffer()
         * and therefore we know it is writable.
         * But on the next rounds, encode() will have called
         * avcodec_send_frame(), and the codec may have kept a reference to
         * the frame in its internal structures, that makes the frame
         * unwritable.
         * av_frame_make_writable() checks that and allocates a new buffer
         * for the frame only if necessary.
         */
        ret = av_frame_make_writable(frame);
        if (ret < 0)
            exit(1);

        /* Prepare a dummy image.
         * In real code, this is where you would have your own logic for
         * filling the frame. FFmpeg does not care what you put in the
         * frame.
         */
        /* Y */
        for (y = 0; y < c->height; y++) {
            for (x = 0; x < c->width; x++) {
                frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
            }
        }

        /* Cb and Cr */
        for (y = 0; y < c->height/2; y++) {
            for (x = 0; x < c->width/2; x++) {
                frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
                frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
            }
        }

        frame->pts = i;

        /* encode the image */
        encode(c, frame, pkt, f);
    }

    /* flush the encoder */
    encode(c, NULL, pkt, f);

    /* Add sequence end code to have a real MPEG file.
     * It makes only sense because this tiny examples writes packets
     * directly. This is called "elementary stream" and only works for some
     * codecs. To create a valid file, you usually need to write packets
     */
    return 0;
}
```

--------------------------------

### workaround Field

Source: https://ffmpeg.org/doxygen/7.0/structFFDXVASharedContext.html

A 64-bit unsigned integer used for workarounds. It is referenced in functions for getting decoder GUIDs and initializing the decoder.

```APIDOC
## ◆ workaround
uint64_t FFDXVASharedContext::workaround
---
Definition at line 90 of file dxva2_internal.h.
Referenced by dxva_get_decoder_guid(), and ff_dxva2_decode_init().
```

--------------------------------

### ff_hpeldsp_init

Source: https://ffmpeg.org/doxygen/7.0/hpeldsp_8h_source.html

Initializes the Half-pel DSP context with default settings.

```APIDOC
## ff_hpeldsp_init

### Description
Initializes the Half-pel DSP context structure.

### Signature
void ff_hpeldsp_init(HpelDSPContext *c, int flags);

### Parameters
- **c** (*HpelDSPContext* *) - Pointer to the HpelDSPContext structure to be initialized.
- **flags** (*int*) - Flags to control initialization behavior.
```

--------------------------------

### Get Relative Time

Source: https://ffmpeg.org/doxygen/7.0/dct_8c_source.html

Retrieves the current time in microseconds relative to an unspecified starting point. Used for performance measurements.

```c
av_gettime_relative()
```

--------------------------------

### Main Function for Audio Encoding Example (C)

Source: https://ffmpeg.org/doxygen/7.0/encode__audio_8c.html

Entry point for the audio encoding example. Parses command-line arguments, initializes the encoder, and processes audio data.

```c
int main(int argc, char **argv)
{
    AVCodec *codec = NULL;
    AVCodecContext *ctx = NULL;
    AVFrame *frame = NULL;
    AVPacket *pkt = NULL;
    FILE *output = NULL;
    enum AVSampleFormat sample_fmt;
    int sample_rate, ret;
    uint8_t *audio_buf = NULL;
    AVChannelLayout dst_ch_layout;

    if (argc <= 2) {
        fprintf(stderr, "Usage: %s <output file> <codec name>\n", argv[0]);
        return 1;
    }

    output = fopen(argv[1], "wb");
    if (!output) {
        fprintf(stderr, "Could not open output file %s\n", argv[1]);
        return 1;
    }

    /* find the encoder */
    codec = avcodec_find_encoder(AV_CODEC_ID_AAC);
    if (!codec) {
        fprintf(stderr, "Codec %s not found\n", argv[2]);
        return 1;
    }

    ctx = avcodec_alloc_context3(codec);
    if (!ctx) {
        fprintf(stderr, "Could not allocate video codec context\n");
        return 1;
    }

    /* put sample parameters into the muxer context */
    ctx->bit_rate = 64000;
    sample_rate = select_sample_rate(codec);
    if (codec->supported_samplerates)
        ctx->sample_rate = sample_rate;
    ret = select_channel_layout(codec, &dst_ch_layout);
    if (ret < 0)
        return 1;
    av_ வழி_channel_layout_copy(&ctx->ch_layout, &dst_ch_layout);

    /* check if the sample format of the codec is supported */
    sample_fmt = check_sample_fmt(codec, AV_SAMPLE_FMT_FLTP);
    if (sample_fmt < 0) {
        fprintf(stderr, "sample format %s is not supported by the encoder\n",
                av_get_sample_fmt_name(AV_SAMPLE_FMT_FLTP));
        return 1;
    }
    ctx->sample_fmt = sample_fmt;

    if (ctx->codec->capabilities & AV_CODEC_CAP_AUTO_THREADS)
        ctx->thread_count = 0;

    /* open the encoder */
    ret = avcodec_open2(ctx, codec, NULL);
    if (ret < 0) {
        fprintf(stderr, "Could not open codec: %s\n", av_err2str(ret));
        return 1;
    }

    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate frame\n");
        return 1;
    }

    frame->nb_samples = ctx->frame_size;
    frame->format = ctx->sample_fmt;
    frame->channel_layout = ctx->ch_layout.u.mask;

    ret = av_frame_get_buffer(frame, 0);
    if (ret < 0) {
        fprintf(stderr, "Could not allocate frame data\n");
        return 1;
    }

    pkt = av_packet_alloc();
    if (!pkt) {
        fprintf(stderr, "Could not allocate packet\n");
        return 1;
    }

    /* encode a frame */
    encode(ctx, frame, pkt, output);

    /* flush the encoder */
    encode(ctx, NULL, pkt, output);

    fclose(output);
    av_frame_free(&frame);
    av_packet_free(&pkt);
    avcodec_free_context(&ctx);

    return 0;
}
```

--------------------------------

### qsv_setup_mids

Source: https://ffmpeg.org/doxygen/7.0/globals_func_q.html

Sets up MIDs for QSV.

```APIDOC
## qsv_setup_mids()

### Description
Sets up the Media SDK (Msdk) internal data structures (MIDs) required for QSV operations.

### Method
N/A (Function Signature)

### Endpoint
N/A

### Parameters
N/A

### Request Example
N/A

### Response
N/A
```

--------------------------------

### Get Current Position in PutByteContext

Source: https://ffmpeg.org/doxygen/7.0/bytestream_8h_source.html

Returns the current offset from the start of the PutByteContext buffer. Useful for tracking write progress.

```c
static av_always_inline int bytestream2_tell_p(PutByteContext *p)
{
return (int)(p->buffer - p->buffer_start);
}
```

--------------------------------

### Initialize AudioIIRContext

Source: https://ffmpeg.org/doxygen/7.0/af__aiir_8c_source.html

Initializes the AudioIIRContext, setting the sample format based on precision and appending output pads for audio and optionally video.

```c
static av_cold int init(AVFilterContext *ctx)
{
    AudioIIRContext *s = ctx->priv;
    AVFilterPad pad, vpad;
    int ret;

    if (!s->a_str || !s->b_str || !s->g_str) {
        av_log(ctx, AV_LOG_ERROR, "Valid coefficients are mandatory.\n");
        return AVERROR(EINVAL);
    }

    switch (s->precision) {
        case 0: s->sample_format = AV_SAMPLE_FMT_DBLP; break;
        case 1: s->sample_format = AV_SAMPLE_FMT_FLTP; break;
        case 2: s->sample_format = AV_SAMPLE_FMT_S32P; break;
        case 3: s->sample_format = AV_SAMPLE_FMT_S16P; break;
        default: return AVERROR_BUG;
    }

    pad = (AVFilterPad){
        .name = "default",
        .type = AVMEDIA_TYPE_AUDIO,
        .config_props = config_output,
    };

    ret = ff_append_outpad(ctx, &pad);
    if (ret < 0)
        return ret;

    if (s->response) {
        vpad = (AVFilterPad){
            .name = "filter_response",
            .type = AVMEDIA_TYPE_VIDEO,
            .config_props = config_video,
        };

        ret = ff_append_outpad(ctx, &vpad);
        if (ret < 0)
            return ret;
    }

    return 0;
}
```

--------------------------------

### Get MF Attribute Size

Source: https://ffmpeg.org/doxygen/7.0/mf__utils_8c_source.html

Retrieves the width and height attributes from an IMFAttributes object. Ensure the GUID is valid and the attributes exist.

```c
#define COBJMACROS
#if !defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0602
#undef _WIN32_WINNT
#define _WIN32_WINNT 0x0602
#endif

#include "mf_utils.h"
#include "libavutil/pixdesc.h"

HRESULT ff_MFGetAttributeSize(IMFAttributes *pattr, REFGUID guid, 
UINT32 *pw, UINT32 *ph)
{
    UINT64 t;

```

--------------------------------

### ff_vk_qf_init

Source: https://ffmpeg.org/doxygen/7.0/hwcontext__vulkan_8c_source.html

Chooses a Queue Family and loads it into a context.

```APIDOC
## ff_vk_qf_init

### Description
Chooses a QF and loads it into a context.

### Signature
```c
int ff_vk_qf_init(FFVulkanContext *s, FFVkQueueFamilyCtx *qf, VkQueueFlagBits dev_family)
```
```

--------------------------------

### Get Stream Filters

Source: https://ffmpeg.org/doxygen/7.0/ffmpeg__mux__init_8c_source.html

Retrieves and sets up filters for video and audio streams. Returns an error code if filter setup fails.

```c
ret = ost_get_filters(o, oc, ost, &filters);
if (ret < 0)
return ret;
```

--------------------------------

### av_xtea_init

Source: https://ffmpeg.org/doxygen/7.0/xtea_8c_source.html

Initialize an AVXTEA context.

```APIDOC
## av_xtea_init

### Description
Initialize an AVXTEA context.

### Signature
```c
void av_xtea_init(AVXTEA *ctx, const uint8_t key[16])
```

### Parameters
*   **ctx** (*AVXTEA* *) - Pointer to the AVXTEA context to initialize.
*   **key** (*const uint8_t[16]*) - The 16-byte encryption key.
```

--------------------------------

### dvdvideo_chapters_setup_simple()

Source: https://ffmpeg.org/doxygen/7.0/dvdvideodec_8c.html

Sets up the chapter information in a simple manner for DVD video.

```APIDOC
## dvdvideo_chapters_setup_simple()

### Description
Sets up chapter information in a simple mode.

### Parameters
- `_s_` (AVFormatContext *) - The AVFormatContext pointer.

### Returns
Returns 0 on success, or an error code on failure.
```

--------------------------------

### AVCodecContext TTA Encoder Setup

Source: https://ffmpeg.org/doxygen/7.0/libavcodec_2ttaenc_8c_source.html

Example of setting up the AVCodecContext for TTA encoding, including closing, encoding callbacks, and supported sample formats.

```c
static const AVCodec ff_tta_encoder = {
    .close = tta_encode_close,
    FF_CODEC_ENCODE_CB(tta_encode_frame),
    .p.sample_fmts = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_U8,
                                                 AV_SAMPLE_FMT_S16,
                                                 AV_SAMPLE_FMT_S32,
                                                 AV_SAMPLE_FMT_NONE },
};
```

--------------------------------

### VAAPI HEVC Start Frame Function

Source: https://ffmpeg.org/doxygen/7.0/vaapi__hevc_8c.html

Initializes the processing for a new HEVC frame using VAAPI. This function is part of the hardware acceleration setup.

```c
static int vaapi_hevc_start_frame(AVCodecContext *avctx, av_unused const uint8_t *buffer, av_unused uint32_t size)
{
**Definition:** vaapi_hevc.c:122
```

--------------------------------

### setup_qtables

Source: https://ffmpeg.org/doxygen/7.0/globals_func_s.html

Sets up quantization tables. Used in mobiclip.c.

```APIDOC
## setup_qtables

### Description
Sets up quantization tables.

### Files
mobiclip.c
```

--------------------------------

### Example Filter Configuration

Source: https://ffmpeg.org/doxygen/7.0/af__arnndn_8c_source.html

Illustrates how to configure a filter, including build system variables and C code integration for image processing.

```text
s EdgeDetect Foobar g libavfilter vf_edgedetect c libavfilter vf_foobar c edit libavfilter and add an entry for foobar following the pattern of the other filters edit libavfilter allfilters and add an entry for foobar following the pattern of the other filters configure make j< whatever > ffmpeg ffmpeg i you should get a foobar png with Lena edge detected That s your new playground is ready Some little details about what s going which in turn will define variables for the build system and the C
```
Tokens:
Raw