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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.

• Compiling FFMPEG on CentOS DigitalOcean

  29 juillet 2015, par coder_uk

  I set up a DigitalOcean instance running CentOS 6.5 and successfully followed the guide to compile FFMPEG (https://trac.ffmpeg.org/wiki/CompilationGuide/Centos). Hurrah !

  But of course I realised that by default, DigitalOcean creates a root user and so ffmpeg now lives in /root/bin/ffmpeg. Which isn’t ideal because when I want to exec the ffmpeg bin from nginx, I would have to run nginx as root for it to have permission.

  Questions ...

  1) Long-shot, but presumably if I change the owner of the ffmpeg binary to nginx, it still won’t work, because nginx won’t be able to access the /root folder it is in. Correct ?

  2) I could run nginx as root (’user root’). But this seems like a very bad idea. Correct ?

  3) Which leaves me with the option of creating a new user, and then compiling ffmpeg into its home folder. But : which user ? EC2 creates ’ec2-user’, so should I make my own equivalent for DO ? But then won’t I have to run nginx as that user, else I’ll run into the same problem ?

  Or should I compile ffmpeg into the ’nginx’ home folder, if indeed it has one ? Is that how it is supposed to be done ?

  Since compiling ffmpeg takes ages, I don’t want to keep doing it, and the static files all seem very out of date. Thanks