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• Detect if an interlaced video frame is the Top or Bottom field ?

  21 décembre 2024, par Danny

  I'm decoding video PES packets (packetized elementary stream) containing H.264/AVC and H.265/HEVC using libavcodec like this :

  


  while (remainingESBytes > 0)
{
    int bytesUsed = av_parser_parse2(
            mpParser, mpDecContext,
            &mpEncPacket->data, &mpEncPacket->size,
            pIn, remainingESBytes,
            AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);

    // send encoded packet for decoding
    int ret = avcodec_send_packet(mpDecContext, mpEncPacket);
    if (ret < 0)
    {
        // failed
        continue;
    }

    while (ret >= 0)
    {
        ret = avcodec_receive_frame(mpDecContext, mpDecFrame);
        /// Do stuff with frame ///
    }

    remainingESBytes = getMoreBytes()
}


  


  Sometimes the input video is interlaced, in which case it seems avcodec_receive_frame is returning individual fields and not a merged frame of the top and bottom fields together.

  


  I couldn't find any way for avcodec_receive_frame to emit a full, non-interlaced frame.

  


  I can merge a top and bottom field together but I haven't found any way to identify if a given AVFrame is top or bottom.

  


  How can I do that ?

  


  EDIT I

  


  Looking at the log output from the decoder, it appears the decoder knows if the field is top or bottom (carried by SEI ?) but still can't figure out how to access that information via the libavcodec API...

  


  [hevc @ 0x1afcfc0] ENTER DECODE NAL TYPE 39. sei.ni_custom.type = -1
[hevc @ 0x1afcfc0] Set sei.ni_custom.type to -1.
[hevc @ 0x1afcfc0] ff_hevc_decode_nal_sei - s->ni_custom.type = -1
[hevc @ 0x1afcfc0] Decoding SEI [NAL Type 39]. ni_custom.type=-1
[hevc @ 0x1afcfc0] TOP Field
[hevc @ 0x1afcfc0] EXIT DECODE NAL TYPE 39. sei.ni_custom.type = -1


  


• FFMpeg Speed up transparent webm C#/Cmd

  17 avril 2023, par Alphapixel 182004

  I am trying to speed up a webm video file while maintaining the transparency but every attempt I've made has removed the transparency.

  


  How do I speed up a transparent webm using FFMpeg without losing the transparency ?

  


  Note : I am doing this all in c# but would prefer to use commands instead of wrapper libraries.

  


  this is the general command I have tried :

  


  command = $"-i \"{input}\" -filter_complex \"[0:v]setpts = (1/{speed}) * PTS[v]; [0:a]atempo = {speed}[a]\" -map \"[v]\" -map \"[a]\" -c:v libvpx-vp9 -b:v 1M -y \"{output}";
That command did not maintain transparency though.

  


  A little info about the input video :

  


  


  • The input is transparent

    


  


  • the input is basically a mess of individual transparent webm's joined together that were made with either :

    


    

    • Poster with audio :

    


    


  


  


  $"-threads 4 -loop 1 -i \"{image}\" -i \"{audio}\" -c:v libvpx-vp9 -pix_fmt yuva420p -crf 10 -b:v 0 -c:a libopus -b:a 192k -shortest -movflags +faststart -y \"{output}\"";

  


  

  • Padding the clip :

  


  


  $"-i \"{input}\" -filter_complex \"[0:v]split=2[v1][v2];[v1]tpad=start_duration={startPadMs / 1000}:start_mode=clone:stop_duration={endPadMs / 1000}:stop_mode=clone[v1_edited];[v1_edited][v2]overlay=eof_action=pass[v];[0:a]adelay={startPadMs}|{startPadMs}[a]\" -map \"[v]\" -map \"[a]\" \"{output}\""

  


  

  • Joining videos :

  


  


  var temp = Path.Combine(Path.GetTempPath(), "concat.txt"); File.WriteAllText(temp, string.Join('\n', clips.Select(e => $"file '{e}'"))); var command = $"-f concat -safe 0 -i "{temp}" -c copy -y "{output}"";\

  


• lavu : add an API function to return the FFmpeg version string

  30 juin 2015, par wm4

  lavu : add an API function to return the FFmpeg version string
  This returns something like "N-73264-gb54ac84". This is much more useful
  
  than the individual library versions, of which there are too much and
  
  which are very hard to map back to releases or git commits.
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] doc/APIchanges
  • [DH] libavutil/avutil.h
  • [DH] libavutil/utils.c