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• change wav sample rate from 22khz to 44khz with ffmpeg [on hold]

  17 mars 2014, par Marc Maxson

  I have wav files that the web browser has recorded using recorder.js at 22.05khz (in order to limit filesize). On the server, I'm using ffmpeg to convert them to 44.1khz MP3 files.

  ffmpeg has pretty good documentation, and I think this ought to do what I want:

  ffmpeg -i ~/webapps/s/audiostory/absquatulate-ko6vc-2014-03-14.wav -ar 44100 test.mp3
  

  but the file still sounds slow. I probed:

  > ffprobe /home/djotjog/webapps/s/audiostory/absquatulate-ko6vc-2014-03-14.wav
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 22050 Hz, 2 channels, s16, 705 kb/s
  > ffprobe test.mp3
  Stream #0:0: Audio: mp3, 44100 Hz, stereo, s16, 128 kb/s
  

  What am I doing wrong? I've tried a bunch of other tricks, including:

  ffmpeg -i ~/webapps/s/audiostory/absquatulate-ko6vc-2014-03-14.wav -ar 44100 -filter:a "aresample=44100" test2.wav (should resample the file)

  and

  ffmpeg -i ~/webapps/s/audiostory/absquatulate-ko6vc-2014-03-14.wav -ar 44100 -filter:a "atempo=2.0" aresample=44100 test2.wav (should double the tempo of the file)

  but they had no effect either.

• libav much longer than avconv

  17 mars 2014, par fsulser

  I was using ffmpeg to generate some images from a video. Now I read that I shouldn't use ffmpeg longer and use avconv from libav instead. So I tried to do the same thing with avconv.

  The ffmpeg is looking like this:

  ffmpeg -ss 1000 -t 5 -i 'test.mp4' -s '120*90' -r 10 out%2d.bmp
  

  Same with avconv:

  avconv -ss 1000 -t 5 -i 'test.mp4' -s '120*90' -r 10 out%2d.bmp
  

  ffmpeg needs less than one second to finish. Avconv about 90 seconds for the same task. Is this usual or do I need to change some things to work with avconv?

• Video conversion using map-reduce

  17 mars 2014, par user3428294

  I have a Ruby on Rails application where users would be uploading videos and I'm looking for a system for converting videos uploaded by the users to FLV format.

  Currently we are using FFMPEG and since video conversion is a heavy task it seems to be taking a lot of time and a lot of CPU resources..

  We are looking if we can use map-reduce / Hadoop framework for implementing video conversion, as it is completely distributed.

  Is it a good option to use map-reduce for video conversion in real time? If it is so, how can that be implemented?

  Note: Each video file size is around 50 - 60 MB.

• FFMpeg -re flag and segmenter. If end of file is reached, wait ?

  17 mars 2014, par user2901994

  This question is similar to

  Keep FFMPEG running and waiting for new image files to encode and stream

  FFMpeg's -re flag tells FFMpeg to "read input at native frame rate". This allows me to continuously append to the end of an audio file, as FFMpeg's segmenter runs, continuing to segment the file that is being appended to (for HLS).

  Is there a way to get FFMpeg to wait, instead of exit, even it it reaches the end of the input file? If say, latency causes FFMpeg to catch up with my appending to the end of the file?

• ffmpeg fix video orientation

  17 mars 2014, par PiTheNumber

  A video can contain a meta info about the camera orientation. For example iPhone and other phones set this flag if you turn the device. Problem is while some player read this info and rotate the video accordingly, other players do not.

  To fix this the video has to be rotated and the meta info needs to be set correctly.

  Does ffmpeg provide a fix for this or do I have to go the hard way (Read rotation, rotate, set meta data)