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• Syncing decoded video using Ffmpeg

  30 juin 2012, par Infiniti Fizz

  I am using Ffmpeg to decode and play video files. I have currently got the video playing and the audio playing at as fast as the CPU can decode and display them. The problem is that I want to play the video and audio in sync using the system clock.

  I've searched around for some help but can't find anything substantial other than dranger's tutorial 05 but I don't really understand what he is doing because my program isn't written in the same way as his.

  I am using mjpeg files and so the pts seems to be retrieved every single time a frame is decoded, I have multiplied the pts by the time_base as dranger does to get the value in seconds but the resolution seems to be only seconds and so I get the value "6" 25 times and then "7" 25 times as the video runs at 25 frames per second.

  Is there not a more accurate value ? Or way to get a more accurate value and if so, how would I go about syncing to this value ? I am using SDL to display the value so can I just use a SDL_Delay() of the value I get ?

  Thanks for your time,

  Infinitifizz

• FFmpeg per stream metadata change with more audio streams

  22 août 2014, par tomasb

  I’m trying to change audio stream title for a movie which was originally with DTS sound. I have added AC3 version using -map parameter, want to keep both. My problem is that the AC3 audio stream bears DTS stream metadata. I am using FFmpeg 1.2

  Tried :

  ffmpeg -i movie.mkv -c copy \
  
  -metadata:s:1 title="AC3 5.1 640 kb/s" -y movie.temp.mkv 

  this partially works, but output file contains only 1 of each stream type, i.e. 1 video, 1 audio and 1 subtitle stream. When i try to get all the streams contained in my mkv like this :

  ffmpeg -i movie.mkv -map 0 \
  
  -metadata:s:1 title="AC3 5.1 640 kb/s" -y movie.temp.mkv 

  i am getting strange output :

  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 -> libx264)
  
    Stream #0:1 -> #0:1 (ac3 -> libvorbis)
  
    Stream #0:2 -> #0:2 (subrip -> ass)
  
    Stream #0:3 -> #0:3 (dca -> libvorbis)
  
    Stream #0:4 -> #0:4 (ac3 -> libvorbis)
  
    Stream #0:5 -> #0:5 (subrip -> ass)
  
  Press [q] to stop, [?] for help
  
  [libvorbis @ 0x12e5a40] Queue input is backward in time
  
      Last message repeated 19 times
  
  Queue input is backward in time      20kB time=00:00:01.05 bitrate= 156.8kbits/s    
  
  [libvorbis @ 0x12e5a40] Queue input is backward in time
  
      Last message repeated 17 times
  
  Queue input is backward in time      20kB time=00:00:01.99 bitrate=  83.0kbits/s    
  
  [libvorbis @ 0x12e5a40] Queue input is backward in time
  
      Last message repeated 5 times
  
  Queue input is backward in time=      20kB time=00:00:02.38 bitrate=  69.5kbits/s    
  
  [libvorbis @ 0x12e5a40] Queue input is backward in time
  
      Last message repeated 6 times
  
  Queue input is backward in time=      20kB time=00:00:02.87 bitrate=  57.5kbits/s    
  
  [libvorbis @ 0x12e5a40] Queue input is backward in time
  
  ...

  I have found information that FFmpeg’s attributes under linux are inconsistent when manipulating per stream metadata and doesn’t work as expected so I am looking for some alternative way how to proceed. (preferably with ffmpeg)

  Thanks for any help.

• How to manipulate YUV frames obtained from an ffmpeg video decoder ?

  23 juillet 2014, par user3665376

  I wanted to apply effects on video while rendering on android . I decoded the mpeg4 video using ffmpeg to raw YUV(YUV420P) frames .

  I modified the Y(luminescence) bytes using the below snippet and rendered it to screen after converting it to RGB frames .

  AVFrame *frame = [YUV420P frame recieved from ffmpeg decoder]
  
  uint8_t *tempPtr = NULL;
  
  tempPtr = frame->data[0];
  
  int j;
  
  for(j = 0 ; j < frame->linesize[0] ; j++){
  
      *(tempPtr++) = 1;
  
  }

  I applied a Y value of 1 to all pixels of all frames . I expected an output video of low luminescence ie.much darker video . But I was not able to notice any change in luma of the rendered video .

  Note : The YCbCr data planes at AVFRame.data[0] , AVFrame.data[1] , Avframe.data[2] of the decoded frame has expected values . The AVFrame.buf pointers were all pointing to NULL (Don’t know whether it has anything to do with data).

  Wanted to know whether anybody has encountered this situation before ??Links to related opics also will be very much helpful.

  Thanks.