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• Cross compile libtheora with msys

  30 septembre 2015, par David

  I don’t really have any experience cross compiling so there is probably a simple solution to my problem. I downloaded libogg 1.3.1 from http://downloads.xiph.org/releases/ogg/libogg-1.3.1.tar.gz and libtheora from http://downloads.xiph.org/releases/theora/libtheora-1.1.1.tar.bz2. First I compile and libogg using these commands (in MSYS, when in the extracted directory) :

  ./configure --prefix=/usr/local/x86_64-w64-mingw32 --host=x86_64-w64-mingw32 --disable-static
  
  make clean && make -j4
  
  make install

  and it looks like everything works (no errors reported and I see libogg files in /usr/local/x86_64-w64-mingw32).

  I also compile and install libvorbis and libSDL with similar commands (downloads found in links on http://www.theora.org/downloads/)

  I then try to compile libtheora and it fails at the configure. Here is the command I run :

  ./configure --prefix=/usr/local/x86_64-w64-mingw32 --host=x86_64-w64-mingw32 --disable-static

  and the result is an error about not finding the libogg library (below is the end of the configure output) :

  checking for OGG... no
  
  checking for Ogg... no
  
  *** Could not run Ogg test program, checking why...
  
  *** The test program failed to compile or link. See the file config.log for the
  
  *** exact error that occured. This usually means Ogg was incorrectly installed
  
  *** or that you have moved Ogg since it was installed.
  
  configure: error:
  
      libogg is required to build this package!
  
      please see http://www.xiph.org/ for how to
  
      obtain a copy.

  Does anyone have any thoughts on what I am doing wrong ?

  Thanks,

  David

• Merge commit '11e225db31dcad57e2219ad8dfae2ac027af53d6'

  20 mai 2017, par Clément Bœsch

  Merge commit '11e225db31dcad57e2219ad8dfae2ac027af53d6'
  * commit '11e225db31dcad57e2219ad8dfae2ac027af53d6' :
  
    rtmp : Account for bytes_read wraparound
  This commit is a noop, see 0849a0ebb2c94856c3a94cb114a1412e44904c28
  Merged-by : Clément Bœsch <u@pkh.me>
  

• Transcode HLS Segments individually using FFMPEG

  27 mai 2013, par rayh

  I am recording a continuous, live stream to a high-bitrate HLS stream. I then want to asynchronously transcode this to different formats/bitrates. I have this working, mostly, except audio artefacts are appearing between each segment (gaps and pops).

  Here is an example ffmpeg command line :

  ffmpeg -threads 1 -nostdin -loglevel verbose \
  
     -nostdin -y -i input.ts -c:a libfdk_aac \
  
     -ac 2 -b:a 64k -y -metadata -vn output.ts

  Inspecting an example sound file shows that there is a gap at the end of the audio :

  

  And the start of the file looks suspiciously attenuated (although this may not be an issue) :

  

  My suspicion is that these artefacts are happening because transcoding are occurring without the context of the stream as a whole.

  Any ideas on how to convince FFMPEG to produce audio that will fit back into a HLS stream ?

  ** UPDATE 1 **

  Here are the start/end of the original segment. As you can see, the start still appears the same, but the end is cleanly ended at 30s. I expect some degree of padding with lossy encoding, but I there is some way that HLS manages to do gapless playback (is this related to iTunes method with custom metadata ?)

  
  

  ** UPDATED 2 **

  So, I converted both the original (128k aac in MPEG2 TS) and the transcoded (64k aac in aac/adts container) to WAV and put the two side-by-side. This is the result :

  
  

  I'm not sure if this is representative of how a client will play it back, but it seems a bit odd that decoding the transcoded one introduces a gap at the start and makes the segment longer. Given they are both lossy encoding, I would have expected padding to be equally present in both (if at all).

  ** UPDATE 3 **

  According to http://en.wikipedia.org/wiki/Gapless_playback - Only a handful of encoders support gapless - for MP3, I've switched to lame in ffmpeg, and the problem, so far, appears to have gone.

  For AAC (see http://en.wikipedia.org/wiki/FAAC), I have tried libfaac (as opposed to libfdk_aac) and it also seems to produce gapless audio. However, the quality of the latter isn't that great and I'd rather use libfdk_aac is possible.