avcodec: not able to decode hevc

Question

I am having trouble decoding a HEVC encoded video with avcodec. Modifying one line of the source allows for decoding mpeg1 which is not what I need.

Thanks

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <libavcodec/avcodec.h>

#define INBUF_SIZE 1024

static void pgm_save(unsigned char *buf, int wrap, int xsize, int ysize,
                     char *filename)
{
    FILE *f;
    int i;

    f = fopen(filename,"wb");
    fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
    for (i = 0; i < ysize; i++)
        fwrite(buf + i * wrap, 1, xsize, f);
    fclose(f);
}

static void decode(AVCodecContext *dec_ctx, AVFrame *frame, AVPacket *pkt,
                   const char *filename)
{
    char buf[1024];
    int ret;

    ret = avcodec_send_packet(dec_ctx, pkt);
    if (ret < 0) {
        fprintf(stderr, "Error sending a packet for decoding\n");
        exit(1);
    }

    while (ret >= 0) {
        ret = avcodec_receive_frame(dec_ctx, frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            return;
        else if (ret < 0) {
            fprintf(stderr, "Error during decoding\n");
            exit(1);
        }

        printf("saving frame %3d\n", dec_ctx->frame_number);
        fflush(stdout);

        /* the picture is allocated by the decoder. no need to
           free it */
        snprintf(buf, sizeof(buf), "%s-%d", filename, dec_ctx->frame_number);
        pgm_save(frame->data[0], frame->linesize[0],
                 frame->width, frame->height, buf);
    }
}

int main(int argc, char **argv)
{
    const char *filename, *outfilename;
    const AVCodec *codec;
    AVCodecParserContext *parser;
    AVCodecContext *c= NULL;
    FILE *f;
    AVFrame *frame;
    uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
    uint8_t *data;
    size_t   data_size;
    int ret;
    AVPacket *pkt;

    filename    = argv[1];
    outfilename = argv[2];

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

    memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);

    codec = avcodec_find_decoder(AV_CODEC_ID_HEVC);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }

    parser = av_parser_init(codec->id);
    if (!parser) {
        fprintf(stderr, "parser not found\n");
        exit(1);
    }

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

    if (avcodec_open2(c, codec, NULL) < 0) {
        fprintf(stderr, "Could not open codec\n");
        exit(1);
    }

    f = fopen(filename, "rb");
    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);
    }

    while (!feof(f)) {
        /* read raw data from the input file */
        data_size = fread(inbuf, 1, INBUF_SIZE, f);
        if (!data_size)
            break;

        /* use the parser to split the data into frames */
        data = inbuf;
        while (data_size > 0) {
            ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
                                   data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
            if (ret < 0) {
                fprintf(stderr, "Error while parsing\n");
                exit(1);
            }
            data      += ret;
            data_size -= ret;


            if (pkt->data) {
                printf("NICE COCK\n");
                decode(c, frame, pkt, outfilename);

            }
        }
    }

    /* flush the decoder */
    decode(c, frame, NULL, outfilename);

    fclose(f);

    av_parser_close(parser);
    avcodec_free_context(&c);
    av_frame_free(&frame);
    av_packet_free(&pkt);

    return 0;
}

Rotem · Answer 1 · 2022-03-05T22:57:08.910

The code sample is working fine.
I guess the problem is in the input file.

For making things reproducible, start by creating an input video file using FFmpeg CLI:

ffmpeg -y -f lavfi -i testsrc=size=192x108:rate=1:duration=10 -vcodec libx265 -pix_fmt yuv420p input.265

The above command creates HEVC (H.265) encoded stream - 10 frames with resolution 192x108 and pixel format YUV420 (synthetic pattern).
The encoded stream is raw video stream (without container).

Notes:

I modified the code a tiny bit - setting output image name to "%s_%03d.pgm".
Set the Command Arguments to: input.265 and output
The output images are Grayscale, because only Y (Luma) color channel is saved.
There is a minor glitch with the last frame, but I suspect it's related to the encoder.

Here is the code sample (with tiny modification):

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//Using extern "C", because the file is built as C++
extern "C" {
#include <libavcodec/avcodec.h>
}

#define INBUF_SIZE 1024

static void pgm_save(unsigned char* buf, int wrap, int xsize, int ysize,
    char* filename)
{
    FILE* f;
    int i;

    f = fopen(filename, "wb");
    fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
    for (i = 0; i < ysize; i++)
        fwrite(buf + i * wrap, 1, xsize, f);
    fclose(f);
}

static void decode(AVCodecContext* dec_ctx, AVFrame* frame, AVPacket* pkt,
    const char* filename)
{
    char buf[1024];
    int ret;

    ret = avcodec_send_packet(dec_ctx, pkt);
    if (ret < 0) {
        fprintf(stderr, "Error sending a packet for decoding\n");
        exit(1);
    }

    while (ret >= 0) {
        ret = avcodec_receive_frame(dec_ctx, frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            return;
        else if (ret < 0) {
            fprintf(stderr, "Error during decoding\n");
            exit(1);
        }

        printf("saving frame %3d\n", dec_ctx->frame_number);
        fflush(stdout);

        /* the picture is allocated by the decoder. no need to
           free it */
        snprintf(buf, sizeof(buf), "%s_%03d.pgm", filename, dec_ctx->frame_number);
        pgm_save(frame->data[0], frame->linesize[0],
            frame->width, frame->height, buf);

        //av_frame_unref(frame);    // <--- I think we need it.
    }

    //av_packet_unref(pkt);  // <--- I think we need it.
}

int main(int argc, char** argv)
{
    const char* filename, * outfilename;
    const AVCodec* codec;
    AVCodecParserContext* parser;
    AVCodecContext* c = NULL;
    FILE* f;
    AVFrame* frame;
    uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
    uint8_t* data;
    size_t   data_size;
    int ret;
    AVPacket* pkt;

    filename = argv[1];
    outfilename = argv[2];

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

    //memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
    memset(inbuf, 0, sizeof(inbuf));

    codec = avcodec_find_decoder(AV_CODEC_ID_HEVC);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }

    parser = av_parser_init(codec->id);
    if (!parser) {
        fprintf(stderr, "parser not found\n");
        exit(1);
    }

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

    if (avcodec_open2(c, codec, NULL) < 0) {
        fprintf(stderr, "Could not open codec\n");
        exit(1);
    }

    f = fopen(filename, "rb");
    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);
    }

    while (!feof(f)) {
        /* read raw data from the input file */
        data_size = fread(inbuf, 1, INBUF_SIZE, f);
        if (!data_size)
            break;

        /* use the parser to split the data into frames */
        data = inbuf;
        while (data_size > 0) {
            ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
                data, (int)data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
            if (ret < 0) {
                fprintf(stderr, "Error while parsing\n");
                exit(1);
            }
            data += ret;
            data_size -= ret;


            if (pkt->data) {
                printf("NICE\n");
                decode(c, frame, pkt, outfilename);
            }
        }
    }

    /* flush the decoder */
    decode(c, frame, NULL, outfilename);

    fclose(f);

    av_parser_close(parser);
    avcodec_free_context(&c);
    av_frame_free(&frame);
    av_packet_free(&pkt);

    return 0;
}

Sample output:
output_001.pgm:

output_002.pgm:

output_003.pgm:

FFmpeg (Libva) version:

FFmpeg 64-bit shared Windows build from www.gyan.dev
Version: 4.4-full_build-www.gyan.dev

As it turns out, yes, I did not encode my video files correctly. They were not without a container. Thank you. — Mišo Barišić, Mar 06 '22 at 14:39

score 1 · Answer 2 · answered Mar 05 '22 at 22:52

See my comment here:

See e.g. linux.amazingdev.com/blog/archives/2011/09/28/tutorial01.c and look for the call to avformat_open_input(), av_find_stream_info () and av_read_frame() (and related code) and use that instead of av_parser_parse2(). Full API docs here: ffmpeg.org/doxygen/trunk/group__lavf__decoding.html

In short, your code is for decoding, but for typical video files, you need a demuxing step also. Your code may work for annex-B HEVC files, but your file is likely TS or MP4 or similar.

As a matter of fact, yes, it was a MP4 or something similar. That was the issue — Mišo Barišić, Mar 06 '22 at 14:40

avcodec: not able to decode hevc

2 Answers2

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