Example using lib{avformat,codec} to demux and decode frames of a container file

libavformat_example.c

// clang -g -O2 -I/usr/include/ffmpeg -lavformat -lavutil -lavcodec avformat_example.c -o avformat_example

#include <assert.h>

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/file.h>

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "usage: <input_file>\n");
        return 1;
    }
    AVFormatContext *fmt_ctx = NULL;
    AVCodec *codec = NULL;
    char *input_filename = argv[1];
    int ret = 0;

    ret = avformat_open_input(&fmt_ctx, input_filename, NULL, NULL); assert(ret == 0);
    ret = avformat_find_stream_info(fmt_ctx, NULL); assert(ret == 0);

    av_dump_format(fmt_ctx, 0, input_filename, 0);

    int videostream = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &codec, 0); assert(videostream >= 0);
    assert(codec);  // codec gets filled in for us
    printf("Video stream is stream %d\n", videostream);
    printf("Codec is %s -- %s\n", codec->name, codec->long_name);
    AVCodecContext *dec_ctx = avcodec_alloc_context3(codec); assert(dec_ctx);
    ret = avcodec_parameters_to_context(dec_ctx, fmt_ctx->streams[videostream]->codecpar); assert(ret == 0);
    ret = avcodec_open2(dec_ctx, codec, NULL); assert(ret == 0);

    AVPacket *pkt = av_packet_alloc(); assert(pkt);
    AVFrame *frame = av_frame_alloc(); assert(frame);

    struct timespec tw1, tw2;
    clock_gettime(CLOCK_MONOTONIC, &tw1);

    size_t frames = 0;
    for(;;) {
        ret = av_read_frame(fmt_ctx, pkt);
        if (ret < 0) break; // TODO flush the decoder
        if (pkt->stream_index == videostream) {
            /* printf("Got packet idx=%d pts=%ld size=%d data=%llx bufsize=%d\n", pkt->stream_index, pkt->pts, pkt->size, (unsigned long long)pkt->data, pkt->buf->size); */
            ret = avcodec_send_packet(dec_ctx, pkt); assert(ret == 0);
            /* printf("%d %d %d %d\n", ret, AVERROR(EAGAIN), AVERROR(EINVAL), AVERROR(ENOMEM)); */
            do {
                ret = avcodec_receive_frame(dec_ctx, frame);
                if (ret < 0) break;
                frames += 1;
                /* printf("frame number %d\n", dec_ctx->frame_number); */
            } while (ret >= 0);
        } else {
        }
    }

    clock_gettime(CLOCK_MONOTONIC, &tw2);
    double elapsed = (1000.0*tw2.tv_sec + 1e-6*tw2.tv_nsec - (1000.0*tw1.tv_sec + 1e-6*tw1.tv_nsec)) / 1000;
    printf("Decoded %ld frames in %.2f seconds : %.2f fps\n", frames, elapsed, (double)frames / elapsed);

    av_frame_free(&frame);
    avcodec_free_context(&dec_ctx);
    av_packet_unref(pkt);
    avformat_close_input(&fmt_ctx);
    avcodec_close(dec_ctx);

    return 0;
}