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• FFMpeg : audio resampling changes slightly the speed of the music [on hold]

  24 octobre 2018, par thenaoh

  In my Android app, I use the FFMpeg library to extract audio samples from an audio file on the fly, and also resample them (since my file is encoded in 44100 Hz, and my device expects 48000 Hz sound).

  The problem is : even if the sound quality is perfect, the speed is a little bit higher than the regular speed of the music.

  The difference is very small (small enough so you won’t hear it), but you can hear it when you play the same song at the same time on a regular player (like VLC for example).

  I think it comes from the resampling, but I don’t know how to fix it.

  Here is my code (I get my samples thanks to the getPcmFloat() function) : https://gist.github.com/mregnauld/2538d98308ad57eb75cfcd36aab5099a

  How can I correct the speed of the music ?

  Thanks for your help.

• ffmpeg : is vidstab multithreaded, and/or is there a way to make it perform better on a very high # of cores ?

  30 juillet 2016, par ljwobker

  I’m working on a project where I use the vidstab ffmpeg plugin to stabilize some videos. I’m lucky enough to have access to an extremely fast x86 machine (2 socket, 16 core, 32 thread) but I can’t seem to keep it busy and I’m trying to figure out if it’s a limitation of the toolchain or the config/commands. The workflow is basically 3 steps :

  1. crop the video in terms of both time and dimension (ffmpeg "crop"
     filter)
  2. run vidstabdetect to identify the transformation corrections
  3. run vidstabtransform to apply the transformation and output the
     final video

  When I run the transcode script on this machine, the "crop" pass executes extremely fast, and the htop output from the machine clearly shows all 32 cores(threads) running at nearly 100%.

  When I run the pass with vidstabdetect, htop clearly shows one core running at/near 100%, with all of the other cores hovering in the "few percent" range, and total CPU utilization for the parent PID hovers near 130%. This leads me to believe there must be only one main processing thread, but also several other smaller threads that are consuming at least some parallel time.

  the vidstabtransform pass looks similar, with one core constantly near 100%, and the rest of the cores hovering in the few percent.

  As far as I can tell, there is no way to parallelize the two vidstab processes, as the transform step is completely dependent on the results of the detection pass. There is a single pass option described in the vidstab docs, but the quality isn’t as good so I’m trying to avoid that.

• How to improve cropping speed without loosing much of video quality in ffmpeg - Android

  27 novembre 2017, par Ashutosh Tiwari

  I have been trying to use ffmpeg for my video editing requirements since few days. I earlier asked posted this : How to increase video encoding speed in ffmpeg ?
  but it did not improve the speed to the extent required, also it reduced quality of the video after the operation.

  I also have tried using concat demuxer command like this :

   //Stream copy command for faster ffmpeg join operation
  
      String[] joinCommand = new String[]{
  
              "-y",
  
              "-f",
  
              "concat",
  
              "-safe",
  
              "0",
  
              "-i",
  
              "" + sdCardPathFile,
  
              "-c",
  
              "copy",
  
              "" + joinedVideoFile.getAbsolutePath()
  
      };

  and then I again tried cropping the video using similar command in the link mentioned above. No matter what but if it is a one minute video, it takes at least 10 to 12 seconds, which I want to be reduced to max 3 to 4 seconds.

  Can someone guide me please ?