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• Why FFMpeg seeking is not working with `av_seek_frame` API ?

  5 décembre 2023, par kakaiikaka

  I'm writing a simple C function to get target(the frame_num's frame) AVFrame. I know about intra-frame staff, so I may need to get several neighbour frames after seeking. But the seek API does not work ; I printed the decoded frame in the inner while the loop was still counting from the first frame in the file.

  


  Why it does not work ? BTW, I'm testing on an H.264 file.

  


  int seekHevcGetFrameToSeconds(const char *filename, int64_t frame_num, AVFrame *frame){
    int ret = 0;
    int video_stream_index = -1;
    AVFormatContext *fmt_ctx = NULL;

    // open input
    if ((ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL)) < 0)
    {
        fprintf(stderr, "Could not open input file '%s' (error '%s')\n",
                filename, av_err2str(ret));
        return ret;
    }

    for (int i = 0; i < fmt_ctx->nb_streams; i++)
    {
        AVStream *stream = fmt_ctx->streams[i];
        AVCodecParameters *codecpar = stream->codecpar;
        if (codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            video_stream_index = i;
            break;
        }
    }

    if (video_stream_index < 0)
    {
        fprintf(stderr, "Could not find video stream in the input, aborting\n");
        ret = -1;
        goto end;
    }

    AVStream *stream = fmt_ctx->streams[video_stream_index];

    // find decoder for the stream
    const AVCodec *codec = avcodec_find_decoder(stream->codecpar->codec_id);

    // allocate a new decoding context
    AVCodecContext *codec_ctx = avcodec_alloc_context3(codec);
  
    if (!codec_ctx)
    {
      fprintf(stderr, "Failed to allocate video codec context\n");
      return -1;
    }
    
    AVBufferRef *hw_device_ctx = NULL;
    int err = 0;
    
    err = av_hwdevice_ctx_create(&hw_device_ctx, AV_HWDEVICE_TYPE_VIDEOTOOLBOX, NULL, NULL, 0);
    if (err < 0)
    {
      fprintf(stderr, "Failed to create a VIDEOTOOLBOX device context\n");
      return -1;
    }
    
    codec_ctx->hw_device_ctx = av_buffer_ref(hw_device_ctx);

    // pass codec parameters to decoding context
    if ((ret = avcodec_parameters_to_context(codec_ctx, stream->codecpar)) < 0)
    {
        fprintf(stderr, "Failed to copy codec parameters to decoder context (error '%s')\n", av_err2str(ret));
        goto end;
    }

    // init the decoders
    if ((ret = avcodec_open2(codec_ctx, codec, NULL)) < 0)
    {
        fprintf(stderr, "Failed to open codec for stream #%u (error '%s')\n", video_stream_index, av_err2str(ret));
        goto end;
    }

    AVPacket *pkt = av_packet_alloc();

    AVRational frame_rate = stream->avg_frame_rate;
    double fps = av_q2d(frame_rate);

    // Calculate the timestamp of the 500th frame in seconds
    double timestamp = frame_num / fps;

    // Convert the timestamp to AVStream.time_base units
    int64_t timestamp_in_time_base_units = timestamp / av_q2d(stream->time_base);
  
    // seek to target timestamp
    if (( ret = av_seek_frame( fmt_ctx, -1, timestamp_in_time_base_units, 0 )) < 0)
    {
        fprintf(stderr, "Failed to seek to target frame (error '%s')\n", av_err2str(ret));
        goto end;
    }

    avcodec_flush_buffers(codec_ctx);

    // read frames from the file
    while (av_read_frame(fmt_ctx, pkt) >= 0)
    {
        if (pkt->stream_index != video_stream_index)
        {
            av_packet_unref(pkt);
            continue;
        }
      
        if (avcodec_send_packet(codec_ctx, pkt) < 0)
        {
            fprintf(stderr, "Error while sending a packet to the decoder\n");
            ret = -1;
            goto end;
        }

        while (avcodec_receive_frame(codec_ctx, frame) == 0)
        {
            printf("Frame %c (%" PRId64 ") pts %" PRId64 " dts %" PRId64 " key_frame %d\n",
                 av_get_picture_type_char(frame->pict_type),
                 codec_ctx->frame_num,
                 frame->pts,
                 frame->pkt_dts,
                 frame->key_frame);
            goto end;
        }
        av_packet_unref(pkt);
    }
    

end:
    av_packet_free(&pkt);
    avcodec_free_context(&codec_ctx);
    avformat_close_input(&fmt_ctx);
    return ret; 
}


  


• avfilter/w3fdif : do not write to line before start line

  22 juillet 2017, par Muhammad Faiz

  avfilter/w3fdif : do not write to line before start line
  That line has been written by previous job.
  
  Fix tsan warning.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Muhammad Faiz <mfcc64@gmail.com>
  

  • [DH] libavfilter/vf_w3fdif.c

• swresample/resample : do not assert compensation_distance on rebuild_filter

  17 mars 2017, par Muhammad Faiz

  swresample/resample : do not assert compensation_distance on rebuild_filter
  when set_compensation is called with zero sample_delta,
  
  compensation does not happen (because dst_incr == ideal_dst_incr)
  
  but compensation_distance is set
  regression since 01ebb57c03abde89bca7bdbc552917efcb8f551d
  Found-by : wm4 <nfxjfg@googlemail.com>
  
  Reviewed-by : wm4 <nfxjfg@googlemail.com>
  
  Signed-off-by : Muhammad Faiz <mfcc64@gmail.com>
  

  • [DH] libswresample/resample.c