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• How to downscale video using subprocess and then piping the data over to stdout and play using ffplay and save it as well

  2 avril 2021, par ZeroDay Fracture

  I am trying to use ffmpeg to downscale a video and pipe the stdout data to ffplay to play the new downsized video by piping it to ffplay on aws lambda.

  


  This is the command I have so far, but for some reason adding a scale option is not working.

  


  I am trying to run this command locally before I deploy it on python with subprocess command. I need the raw video to be able to save into database for streaming the data in realtime.

  


  %ffmpeg -i sample.mp4  -vf scale=240:-2 -f  mpegts -c:v copy -af aresample=async=1:first_pts=0 - | ffplay -

  


  adding the scale optioin for some reason is saving the video as the name scale=240 :-2 which does not make sense.

  


• lavf/webvttdec : save cue id and settings as side data

  1er juin 2013, par Matthew Heaney

  lavf/webvttdec : save cue id and settings as side data
  Currently the WebVTT demuxer parses the cues but throws away
  
  the cue id (the optional first line of the cue) and cue
  
  settings (the optional rendering instructions that follow
  
  the timestamp).
  However, in order to write inband text tracks (to WebM
  
  files), the entire cue payload from the WebVTT source must
  
  be preserved.
  This commit makes no change to the data part of the output
  
  buffer packet (where the actual cue text is stored), but
  
  does add the cue id and settings as a side data items, if
  
  they’re present in the cue. Existing code that cares only
  
  about the data part of the packet can continue to ignore the
  
  side data.
  There are two new packet data type flags,
  
  AV_PKT_DATA_WEBVTT_IDENTIFIER and
  
  AV_PKT_DATA_WEBVTT_SETTINGS.
  

  • [DH] libavcodec/avcodec.h
  • [DH] libavcodec/version.h
  • [DH] libavformat/webvttdec.c

• save row ffmepg data packets as a video

  7 août 2019, par MattéoLuci

  I have modified the muxing.c ffmpeg example program to be able to save a video from the PC or on an RTSP stream, and it works quite good.
  I would like to make the video saving as fast and efficient as possible by saving directly the packets without changing them into AVFrames (I don’t need to print them).

  I tried to save the AVPacket coming from av_read_frame(InFmtCtx, &packet) with av_write_frame(OutFmtCtx, &packet).

  AVPacket packet;
  
  static int count = 0;
  
  while (av_read_frame(InFmtCtx, &packet)>=0) {
  
     if(packet.stream_index == videoStream) {
  
  
  
         packet.dts = count;
  
         packet.pts = count++;
  
  
  
         av_packet_rescale_ts(&packet, ost->enc->time_base, 
  
                                           ost->st->time_base);
  
         packet.stream_index = ost->st->index;
  
         if (av_write_frame(OutFmtCtx, &packet) < 0) {
  
            fprintf(stderr, "Error writing video frame: \n");
  
            exit(1);
  
         }
  
         ost->enc->frame_number++;
  
     }
  
  }

  The program runs correctly and the video file has the right size and the right duration.
  When I run it with VLC or ffmpeg it shows no error message, the time runs correctly, but no image is printed