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• How to get native frame rate of vide with FFmpex ?

  18 juin 2021, par Flame_Phoenix

  Background

  


  I have an .mp4 video and I need to get the video's frame rate. Using ffmepg (in Linux) I know I can get this information via the following command :

  


  ffprobe -v 0 -of compact=p=0 -select_streams 0 -show_entries stream=r_frame_rate 'MyVideoFIle.mp4'


  


  Which returns :

  


  r_frame_rate=24000/1001


  


  FFmpex

  


  Doing this in bash is fine, but what I really want is to use it in my Elixir application. To this end I found out about ffmpex.

  


  First I tried using FFprobe :

  


  > FFprobe.format("Devil May Cry 5 Bury the Light LITTLE V COVER.mp4")

{:ok,
 %{
   "bit_rate" => "611784",
   "duration" => "482.999000",
   "filename" => "Devil May Cry 5 Bury the Light LITTLE V COVER.mp4",
   "format_long_name" => "QuickTime / MOV",
   "format_name" => "mov,mp4,m4a,3gp,3g2,mj2",
   "nb_programs" => 0,
   "nb_streams" => 2,
   "probe_score" => 100, 
   "size" => "36936415",
   "start_time" => "0.000000",
   "tags" => %{
     "compatible_brands" => "isomiso2avc1mp41",
     "encoder" => "Lavf58.19.102",
     "major_brand" => "isom",
     "minor_version" => "512"
   }
 }}


  


  Which gives me some information, but not the frame rate.

  


  My next tentative was to use the command options :

  


  command = 
  FFmpex.new_command() 
  |> add_input_file("Devil May Cry 5 Bury the Light LITTLE V COVER.mp4") 
  |> add_video_option(???) 


  


  But the problem here is that I can't find in the documentation the video option I need to get the native frame rate. I only found vframe which is used to set the video frame rate.

  


  Question

  


  

  • How can I get the native fps of a video using ffmpex ?

  


  


• Remove some redundant NULL checks and fix a free on error return.

  3 mars 2012, par Tim Terriberry

  Remove some redundant NULL checks and fix a free on error return.
  ref_frame_data was being allocated with the aligned allocator, but
  
   freed with the normal _ogg_free() function on failure, which
  
   doesn’t work.
  
  This would only cause a problem if there was just enough memory to
  
   satisfy the reference frame allocation (just over 4.5 or 9 bytes
  
   per pixel) but not enough for the fragment buffer offets (1/16 or
  
   1/8th byte per pixel).
  git-svn-id : http://svn.xiph.org/trunk/theora@18219 0101bb08-14d6-0310-b084-bc0e0c8e3800
  

  • [DH] lib/internal.c
  • [DH] lib/state.c

• Exception thrown at 0x00007FFC0B57BCEF (swscale-6.dll) in App.exe : 0xC0000005 : Access violation reading location 0xFFFFFFFFFFFFFFFF

  9 novembre 2023, par JIUN-YU

  Trying to play a video using FFmpeg on visual studio 2022 on windows 10.
Exception is thrown at sws_scale in the code. Don't know why this is occurred.
It is worth noting that this error sometimes occurs when reading the camera and sometimes it does not.

  


  here is my code

  


  bool CalibrationPanel::video_reader_read_frame(VReaderState* state, cv::Mat cvimg)
{
    // Unpack members of state
    auto& width = state->width;
    auto& height = state->height;
    auto& av_format_ctx = state->av_format_ctx;
    auto& av_codec_ctx = state->av_codec_ctx;
    auto& video_stream_index = state->video_stream_index;
    auto& av_frame = state->av_frame;
    auto& av_packet = state->av_packet;
    auto& sws_scaler_ctx = state->sws_scaler_ctx;


    // Decode one frame
    int response;
    while (av_read_frame(av_format_ctx, av_packet) >= 0)
    {
        if (av_packet->stream_index != video_stream_index)
        {
            av_packet_unref(av_packet);
            continue;
        }

        response = avcodec_send_packet(av_codec_ctx, av_packet);
        if (response < 0)
        {
            char errStr[256] = {0};
            av_strerror(response, errStr, sizeof(errStr));
            printf("Failed to decode packet: %s\n", errStr);
            return false;
        }

        response = avcodec_receive_frame(av_codec_ctx, av_frame);
        if (response == AVERROR(EAGAIN) || response == AVERROR_EOF)
        {
            av_packet_unref(av_packet);
            continue;
        }
        else if (response < 0)
        {
            char errStr[256] = {0};
            av_strerror(response, errStr, sizeof(errStr));
            printf("Failed to decode packet: %s\n", errStr);
            return false;
        }

        av_packet_unref(av_packet);
        break;
    }
    int64_t* pts = &ppts;
    *pts = av_frame->pts;

    // Set up sws scaler
    if (!sws_scaler_ctx)
    {
        sws_scaler_ctx = sws_getContext(width, height, av_codec_ctx->pix_fmt,
                                        width, height, AV_PIX_FMT_BGR24,
                                        SWS_BILINEAR, NULL, NULL, NULL);
        if (!sws_scaler_ctx)
        {
            printf("Couldn't initialize sw scaler\n");
            return false;
        }
    }


    // Creating an image space to hold YUV images
    AVFrame* frameYUV = av_frame_alloc();
    auto* out_buffer = (unsigned char*)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_BGR24, width, height, 1));
    av_image_fill_arrays(frameYUV->data, frameYUV->linesize, (const uint8_t*)out_buffer, AV_PIX_FMT_BGR24, width, height, 1);

    uint8_t* dest[4] = {cvimg.data, NULL, NULL, NULL};
    sws_scale(sws_scaler_ctx, av_frame->data, av_frame->linesize, 0, av_frame->height, dest, frameYUV->linesize);

    return true;
}


  


  fixed this bug, so it's not luck that makes the camera turn on every time.