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• Turn a video into a sequence of images using GStreamer (not ffmpeg)

  12 août 2021, par Rory

  I have an ogg vorbis video. It plays fine in totem and mplayer. I want to covert it to a sequnces of images, one image per frame. I can do this on ffmpeg with the following command :

  



  ffmpeg -i video.ogv -f image 2 video-frames-%08png


  



  However that doesn't work for this video. Each frame is all grey as if there has been loads of decoding problems. Since it works in totem, I suspect that gstreamer is better able to decode the video than ffmpeg. Is there a gstreamer command that will take in a ogg vorbis video and then create a pile of images, one for each frame ?

  



  I'm using stock Ubuntu Lucid desktop.

  


• Révision 18240 : Theme SPIP de base tire de Fatcow http://zone.spip.org/trac/spip-zone/browser/_c...

  24 juillet 2011, par cedric -

• Can Codec Time Base (tbc) break video playback ?

  8 juillet 2019, par Adam Szmyd

  I have an app WebRTC conferencing app that is recording user’s video feed and produces an mp4 out of it.

  I’m using h264 codec and I’m first generating mkv file directly using ffmpeg and Java wrapper for it (https://github.com/bytedeco/javacpp).

  The output mkv is playable properly using VLC but it’s not playable at all in OSX QuickTime. I’m trying to convert to MP4 in order to make it work in OSX properly. I’m trying to avoid re-encoding as i’t quite slow process and i already have encodec h264 video packets so it shouldn’t be needed.

  I have very basic example file which is just an video of 30 frames where 1st is an keyframe (I-Frame) and rest are P-Frames.

  When i try to convert my mkv to mp4 using such command :

  ffmpeg -i input.mkv -vcodec copy output.mp4

  It opens in QuickTime but shows no content (black frame, no errors)

  When i re-encode my mkv to the same format and profile with ffmpeg :

  ffmpeg -i output.mkv -profile:v baseline output-reencoded.mkv

  And convert it again to mp4 :

  ffmpeg -i input-reencoded.mkv -vcodec copy output-reencoded.mp4

  It WORKS. But it is re-encoding and for large files it takes ages.

  I’m trying to compare what’s the difference between my source mkv and the one processed by ffmpeg. First noticable difference is tbc (which is an timebase for codec) :

  $ ffprobe -hide_banner input.mkv 
  
  Input #0, matroska,webm, from 'input.mkv':
  
    Metadata:
  
      ENCODER         : Lavf58.12.100
  
    Duration: 00:00:00.75, start: 0.000000, bitrate: 228 kb/s
  
      Stream #0:0: Video: h264 (Constrained Baseline), yuv420p(progressive), 1920x1080, 40 fps, 40 tbr, 1k tbn, 2k tbc (default)
  
      Metadata:
  
        DURATION        : 00:00:00.750000000
  
  
  
  $ ffprobe -hide_banner output-reencoded.mkv
  
  Input #0, matroska,webm, from 'output-reencoded.mkv':
  
    Metadata:
  
      ENCODER         : Lavf57.83.100
  
    Duration: 00:00:00.75, start: 0.000000, bitrate: 209 kb/s
  
      Stream #0:0: Video: h264 (Constrained Baseline), yuv420p(progressive), 1920x1080, 40 fps, 40 tbr, 1k tbn, 80 tbc (default)
  
      Metadata:
  
        ENCODER         : Lavc57.107.100 libx264
  
        DURATION        : 00:00:00.750000000

  Note the tbc difference - mine is 2k and ffmpeg’s is 80.

  So first question is : Can it be a reason why it’s not playable by QuickTime ?

  I tried to "force" changing this tbc with various parameters found on web :

  ffmpeg -i input.mkv -x264-params timebase=30 -vcodec copy input2.mkv
  
  ffmpeg -i input.mkv -time_base 1/30 -vcodec copy input2.mkv
  
  ffmpeg -i input.mkv -video_track_timescale 30 -vcodec copy input2.mkv
  
  ffmpeg -i input.mkv -video_track_timescale 30 -vcodec copy input2.mkv

  with no luck. output2.mkv always results with the same 2k tbc.

  I tried changing framerate also and in theory ffmpeg was aiming to make 80 tbc but looks like it didn’t ? :

  $ ffmpeg -i input.mkv -hide_banner -vcodec copy -r 80 input2.mkv
  
  Input #0, matroska,webm, from 'input.mkv':
  
    Metadata:
  
      ENCODER         : Lavf58.12.100
  
    Duration: 00:00:00.75, start: 0.000000, bitrate: 228 kb/s
  
      Stream #0:0: Video: h264 (Constrained Baseline), yuv420p(progressive), 1920x1080, 40 fps, 40 tbr, 1k tbn, 2k tbc (default)
  
      Metadata:
  
        DURATION        : 00:00:00.750000000
  
  Output #0, matroska, to 'input2.mkv':
  
    Metadata:
  
      encoder         : Lavf57.83.100
  
      Stream #0:0: Video: h264 (Constrained Baseline) (H264 / 0x34363248), yuv420p(progressive), 1920x1080, q=2-31, 40 fps, 40 tbr, 1k tbn, 80 tbc (default)
  
      Metadata:
  
        DURATION        : 00:00:00.750000000
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
  Press [q] to stop, [?] for help
  
  frame=   30 fps=0.0 q=-1.0 Lsize=      21kB time=00:00:00.72 bitrate= 236.1kbits/s speed=2.58e+03x    
  
  video:20kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 4.470772%
  
  $ ffprobe -hide_banner input2.mkv 
  
  Input #0, matroska,webm, from 'input2.mkv':
  
    Metadata:
  
      ENCODER         : Lavf57.83.100
  
    Duration: 00:00:00.75, start: 0.000000, bitrate: 228 kb/s
  
      Stream #0:0: Video: h264 (Constrained Baseline), yuv420p(progressive), 1920x1080, 40 fps, 40 tbr, 1k tbn, 2k tbc (default)
  
      Metadata:
  
        DURATION        : 00:00:00.750000000

  Maybe I’m just looking at it wrong and ffprobe is just weirdly calculating tbc but I cannot find other differences between these files and definitely ffmpeg is doing something smart that is "fixing" the mkv. I’d like to do that when i’m creating MKV on my own.