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• Writing multithreaded video and audio packets with FFmpeg

  27 février 2017, par Robert Jones

  I couldn’t find any information on the way av_interleaved_write_frame deals with video and audio packets.

  I have multiple audio and video packets coming from 2 threads. Each thread calls a write_video_frame or write_audio_frame, locks a mutex, initialize an AVPacket and writes data to an .avi file.

  Initialization of AVCodecContext and AVFOrmatContext is ok.

  — Edit 1 —

  Audio and video are coming from an external source (microphone and camera) and are captured as raw data without any compression (even for video).
  I use h264 to encode video and no compression for Audio (PCM).

  Audio captured is : 16bits, 44100khz, stereo

  Video captured is 25FPS

  Question :

  1) Is it a problem if I write multiple video packets at once (let’s say 25 packets/sec) and just one audio packet/sec.

  Answer : Apparently not, the function av_interleaved_write_frame should be able to manage that kind of data as soon as pts and dts is well managed

  This means I call av_interleaved_write_frame 25 times for video writing and just 1 for audio writing per second. Could this be a problem ? If it is how can I deal with this scenario ?

  2) How can I manage pts and dts in this case ? It seems to be a problem in my application since I cannot correctly render the .avi file. Can I use real time stamps for both video and audio ?

  Answer : The best thing to do here is to use the timestamp given when capturing audio / video as pts and dts for this kind of application. So these are not exactly real time stamps (from wall clock) but media capture timestamps.

  Thank you for your precious advices.

• PHP/FFMPEG - why does my video conversion result in empty file ?

  4 novembre 2018, par Utkanos

  I’m trying to convert a video that lives on my server from a .webm to a .mp4.

  shell_exec('ffmpeg -i file.webm output.mp4');

  However, this results in an empty mp4 (0 bytes - or, sometimes, and very weirdly, 28 bytes.) The input file exists, and is 45MB.

  This answer recommended explicitly copying the input codec, but same result.

  shell_exec('ffmpeg -i file.webm -vcodec copy -acodec-copy output.mp4');

  What am I doing wrong ?

  [ ===== EDIT ===== ]

  After trying a few more things, inspired by the comments, I’m still having no joy converting to MP4.

  It seems I’m running FFMPEG v.2.8.15. This seems quite a lot lower than the current release of 4 , however I only installed this a week or so ago so I’m not sure why this is the case and I don’t know how to update it (I’m on WHM Cpanel.)

  Anyway, my problem is NOT to do with pathing, because the same command works fine if I change .mp4 to .webm - I get a successfully converted .webm file.

  But when I run :

  $foo = shell_exec('ffmpeg -i file.webm -vcodec copy -acodec copy output3.mp4 -report');

  ...I get this FFMPEG log output.

  I’ve also tried :

  shell_exec('ffmpeg -fflags +genpts -i file.webm -r 24 KKK.mp4 -report');

  ...from this answer, and

  shell_exec(’ffmpeg -i file.webm -c:v copy III.mp4’) ;

  ...from this article.

  Both result in the same problem, i.e. an 0-bytes .mp4 file.

• Images to video in PHP with FFmpeg

  14 mars 2013, par Boris Kremenovic

  I got a terrible problem. I've been searching, and google-ing my whole day and can't find the answer to this problem..

  I am trying to convert 5 pictures to video using FFmpeg in PHP. I have FFmpeg extension installed in my php.ini.

  Trying running this command :

  <?php
  
  exec("ffmpeg -r 25 -qscale 2 -i %05d.jpg output.mp4");
  
  ?>

  but it gives me a blank page with no errors or something. Can anybody help me ?