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• Removing Silence from m4a files using ffmpeg

  27 juin 2015, par Tejas Shah

  I have an audio file which has both leading and trailing silence and with the following specifics :

  Codec : MPEG AAC Audio (mp4a) Channels : Stereo Sample rate : 44100 Hz Bitrate : 253 kbps

  I want to remove the silences AND keep the quality intact.

  So far I’ve tried

  ffmpeg -i 1.m4a -af silenceremove=1:0.5:0:1:0.5:0 2.m4a 

  This is supposed to remove both the leading and trailing silences.
  But for some reason it doesn’t remove the trailing silence. This seems to be a recurring problem. Found the following on another forum.

  http://ffmpeg-users.933282.n4.nabble.com/How-to-delete-digital-silence-tp4667256p4667356.html

  Also, ffmpeg reduces the bitrate to 128kbps. This I could fix by adding -ab 253k and making the command :

  ffmpeg -i 1.m4a -af silenceremove=1:0.5:0:1:0.5:0 -ab 253k 3.m4a 

  Now the problem is that the trailing silence isn’t removed and when I want to process a batch of files I can’t use the same bitrate (like 253kbps ) for every file. I’d like to know how VBR could be used for this case.

  I know I can use sox and use the silence and reverse features to trim the silences.

  http://digitalcardboard.com/blog/2009/08/25/the-sox-of-silence "Example 3 in this post"

  But sox has the following problems :

  1. It can’t handle m4a files, I had to convert all files to mp3.

  2. When using the silence filter in sox it caps the bitrate at 128kbps.

     sox 1.mp3 2.mp3 silence 1 0.5 1% reverse silence 1 0.5 1% reverse

• Using FFMPEG library with iPhone SDK for video encoding

  21 juin 2015, par user203349

  I need to encode several pictures shot by the iphone camera into a mp4 video file and I know FFMPEG can do this (the application TimeLapser and ReelMoments do it already). I plan to use this in my app iMotion (available in the appstore).

  I successfully install and compile the ffmpeg for the iphone SDK with this link :
  http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/2009-October/076618.html

  But now I’m stuck here in my XCode project. What should I do next to use the FFMPEG library for video encoding ? The Apple documentation about external library using is very light and I just can find any tutorial on the web wich explain how to do this.

  If anybody can help me, I would be very grateful..`

  Thanks

  Aurelien Potier

• aac : Support channel configurations 11 and 12

  4 juin 2015, par Sebastian Dröge

  aac : Support channel configurations 11 and 12
  These are defined in ISO/IEC 14496-3:2009/PDAM 4 for 6.1 and 7.1.
  
  It also defines another 7.1 layout with configuration 14, that one
  
  is not added here for now.
  11 : 3/3.1    FC FL+FR BL+BR BC LFE
  
  12 : 3/2/2.1  FC FL+FR SiL+SiR BL+BR LFE
  Signed-off-by : Luca Barbato <lu_zero@gentoo.org>
  

  • [DH] libavcodec/aacdec.c
  • [DH] libavcodec/aacdectab.h