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• Low-bitrate webm video taking a long time to start on Chrome ?

  11 mai 2017, par user1582024

  I’m doing a project that involves generating a video live stream, but I seem to have run into a strange issue.

  I’m currently using ffmpeg to encode a raw video feed, which I then pipe out to a browser over http. It seems to be working, but for some reason the video takes a rather long time to start in Chrome after I begin streaming.

  I call ffmpeg like this :

  new ProcessBuilder("ffmpeg",
  
                  "-f", "rawvideo",
  
                  "-pixel_format", "rgb24",
  
                  "-video_size", "60x179", // << Note the small resolution
  
                  "-framerate", "25",
  
                  "-r", "25",
  
                  "-i", "-",
  
                  "-vcodec", "libvpx",
  
                  "-f", "webm",
  
                  "-g", "1",
  
                  "-y",
  
                  "pipe:1").redirectError(ProcessBuilder.Redirect.INHERIT)
  
                  .start();

  On Chrome, I simply use a tag with the http resource as the src.

  Firefox starts the video near-instantly, and if I capture the bytes and save them as a file, both the GNOME video player and VLC can read the file with no problems, even if I truncate the file so the remaining video is shorter than the time it takes to start on Chrome.

  This leads me to believe the video stream itself is more or less OK, at least not corrupt and reaching the browser. Chrome also eventually plays the whole video, just with a big delay (yet it is smooth once it starts playing).

  The issue also seems to be dependent on the bitrate of the video, and is especially visible if the bitrate is very low. For example, if I just have a completely black video with a single flashing pixel (very low bitrate), it easily takes 10 seconds to start on Chrome, while if I generate noise (which leads to a high bitrate), this goes more towards 1 second.

  Is there something I can do to make it go faster ?

• avformat/mxfenc : support XAVC long gop

  18 octobre 2018, par Baptiste Coudurier

  avformat/mxfenc : support XAVC long gop
  

  • [DH] libavformat/Makefile
  • [DH] libavformat/avc.c
  • [DH] libavformat/avc.h
  • [DH] libavformat/hevc.c
  • [DH] libavformat/mxf.h
  • [DH] libavformat/mxfenc.c

• ffmpeg : given a video of any length, create timelapse video of 6-8 seconds long

  14 mai 2018, par CDub

  I have an application which consumes video of any length (could be a few seconds, could be several minutes) and I want to use ffmpeg to return a "timelapse" version of the input video which will always be between 6 and 8 seconds long.

  I’ve been fiddling with the following :

  ffmpeg -y -i in.mp4 -r 10 -vf setpts='0.01*PTS' -an out.mp4

  Which seems to be a good start, but still generates very dynamic results given what in.mp4 is.

  I also don’t fully understand the verbiage in the ffmpeg documentation, so I’m not even sure what arguments to use for setpts, or if setpts is the correct filter I want to use.