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• Fastest way to compress video on Android with ffmpeg

  11 septembre 2015, par James Nguyen

  I’m using ffmpeg to lower the filesize of a video on Android.

  I’m using this command.

  "-i input -crf 28 -vf scale=’if(gt(iw,ih),640,trunc(oh*a/2)*2)’ :’if(gt(iw,ih),trunc(ow/a/2)*2,640)’ -acodec copy -preset ultrafast -tune fastdecode -tune zerolatency output"

  The time to compress this video is twice the duration of the video. (1 minute video = 2 minute time to convert) Is there a way to speed this conversion up ?

  Whatsapp seems to do it at almost a 1:1 ratio (time to encode:duration of video).

• mpegts muxer, DVB subtitles encoder : common DVB subtitles payload

  11 janvier 2014, par Serhii Marchuk

  mpegts muxer, DVB subtitles encoder : common DVB subtitles payload
  Improved DVB subtitles encoder to generate AVPacket.data in the same
  
  format as generates MPEGTS demuxer + DVB subtitles parser. So now single
  
  format of DVB subtitles data is used across all the components of FFmpeg :
  
  only subtitles payload WITHOUT 0x20 0x00 bytes at the beginning and 0xFF
  
  trailing byte.
  Improved MPEGTS muxer to support format of DVB subtitles in
  
  AVPacket.data described above : while muxing we add two bytes 0x20 0x00 to
  
  the beginning of and 0xFF to the end of DVB subtitles payload.
  The patch fixes DVB subtitle copy problems : tickets #2989 fully and #2024
  
  partly.
  Signed-off-by : Clément Bœsch <u@pkh.me>
  

  • [DH] libavcodec/dvbsub.c
  • [DH] libavcodec/version.h
  • [DH] libavformat/mpegtsenc.c
  • [DH] libavformat/version.h

• FFMpeg compress with wrong frame rate while sending raw pixel data from java application

  11 janvier 2014, par Marco

  I am trying to create a compressed h264 video file from a series of raw rgb24 pixel data.
  Pixel data is streamed from java application to ffmpeg.exe which is its subprocess.

  For testing purposes I've created a byte array with rgb24 pixel data and then sent it to ffmpeg's input stream.

  Everything works fine except one issue.

  It looks like the frame rate of the encoded file is wrong.
  FFMpeg should compress the video file with 30fps rate (-r 30).

  I am sending 30*20 frames. So I supposed to get a video file with length of 20 seconds.
  But instead of that the video file's length is 24 seconds.
  When I check the compressed file properties, it shows 30fps as expected.

  It looks like the ratio between expected and actual frame rate is 5 to 6 (20 —> 24,30 —> 36).
  I have also tried to stream rgb32 pixel data but I had the same results.

  code :

      ByteArrayOutputStream byteArray = new ByteArrayOutputStream();
  
      //building the frame
  
      for (int i=0; i<1024*800; i++)
  
      {
  
          byteArray.write(i&0xFF);    //r
  
          byteArray.write(i&0xFF);    //g
  
          byteArray.write(i&0xFF);    //b
  
      }
  
  
  
      byte pixelData[] = byteArray.toByteArray();
  
  
  
      File ffmpeg_output_msg = new File("ffmpeg_output_msg.txt");
  
  
  
      ProcessBuilder pb = new ProcessBuilder("ffmpeg.exe","-vcodec","rawvideo","-f","rawvideo","-pix_fmt","rgb24","-s","1024x800","-i","pipe:0","-r","30","-y","-c:v","libx264","out.mkv");
  
  
  
      pb.redirectErrorStream(true);
  
      pb.redirectOutput(ffmpeg_output_msg);
  
  
  
      Process p = pb.start();
  
      OutputStream ffmpegInput = p.getOutputStream();
  
  
  
      //30fps, 20secs
  
      for(int i=0;i<30*20;i++)
  
      {
  
          ffmpegInput.write(pixelData);
  
      }
  
      ffmpegInput.flush();
  
      ffmpegInput.close();

  Any ideas what could be the origin of that problem ?
  Thanks in advance

  UPDATE
  I have changed the frame rate to other values and it looks like the ffmpeg completely ignores that parameter. It always uses 25fps.
  using "-r 30" effects only on the data that's written in file's properties
  (Video : MPEG4 Video (H264) 1024x800 30fps [Video])

  Is it possible that there are two different framerates in the encoded file ?