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• FFMPEG - Struggling to find correct input audio codec parameters on macOS

  20 septembre 2024, par Xavi

  I am trying to read my external stereo microphone with ffmpeg within my Qt Windows+macOs application, but I am struggling to obtain consistent correct input codec parameters on macOs. My findings and suspicions so far :

  


  The code I'm using in macOs is the following, where everything returns a successful return code :

  


   avdevice_register_all();
 
 //macOs only, the same code in windows looks for "dshow" 
 const AVInputFormat *inputFormat = av_find_input_format("avfoundation");
 
 AVFormatContext* inputFormatContext;
 avformat_open_input(&inputFormatContext, inputDevice, inputFormat, NULL);

 avformat_find_stream_info(inputFormatContext, NULL);
 
 //... allocate the codec context for the single input stream and
 // copy the parameters from the stream to the context



  


  In my standalone minimal reproducer this always results on the codec ID of the single stream being AV_CODEC_ID_PCM_F32LE, in both macOS and Windows. When I integrate this code in my Qt application on Windows, I get the same result. However, on macOS, most of the times results in the codec id of the stream being AV_CODEC_ID_PCM_S16LE (via AV_CODEC_ID_FIRST_AUDIO) and sometimes AV_CODEC_ID_PCM_F32LE. Both sample formats are supported by my microphone.

  


  AV_CODEC_ID_PCM_F32LE always results in a correct output. AV_CODEC_ID_PCM_S16LE results on buzzy noisy audio slowed down to 0.5x, and If in this case I decode with AV_CODEC_ID_PCM_F32LE instead of copying the codec parameters from the stream, the output sounds correct again.

  


  I am trying to write generic code, so while enforcing the AV_CODEC_ID_PCM_F32LE codec works, I'd rather understand what is happening.

  


  What am I missing ? Is Qt interacting in some way that I can't think of ? I am compiling and linking my own ffmpeg libraries (6.1.1) and not using Qt's ones.

  


• matroskaenc : implement CueRelativePosition

  23 juillet 2013, par Bernie Habermeier

  matroskaenc : implement CueRelativePosition
  This is a minimal change to matroskaenc that implements CueRelativePosition in the output.
  
  Most players will probably ignore this additional information, but it is in the
  
  matroska spec, and it’d be nice to be able to make use of it.
  Signed-off-by : Bernt Habermeier <bernt@wulfram.com>
  
  Tested-by :  wm4 <nfxjfg@googlemail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavformat/matroska.h
  • [DH] libavformat/matroskaenc.c
  • [DH] tests/ref/lavf/mkv

• Ffmpeg Android - Minimum binary size to convert WAV to MP3

  22 novembre 2020, par timson

  The only thing I want to do is convert wav files to mp3 inside my Android application.

  


  I am currently using https://github.com/tanersener/mobile-ffmpeg and with audio-release everything is working fine. As the lib size is about 40 MB and I only need a single command, I'd like to build my own .aar file as described in the Wiki to reduce the application size.

  


  I edited the android-ffmpeh.sh ./configure:

  


  --disable-everything \    
--enable-pthreads \
--enable-avcodec \
--enable-avformat \
--enable-swresample \
--enable-avfilter \
--enable-libmp3lame \
--enable-parser=mpegaudio \
--enable-demuxer=mp3,wav,pcm_s16le \
--enable-muxer=mp3,wav,pcm_s16le \
--enable-decoder=pcm*,mp3*,wav,pcm_s16le \
--enable-encoder=pcm*,pcm_s16le,wav,mp3,libmp3lame \
--enable-filter=aresample \
--enable-protocol=file \


  


  and then ran ./android.sh -l --enable-lame --enable-libiconv

  


  In my Android app FFmpeg loads but the conversion doesn't succed with following error :

  


  E/mobile-ffmpeg: [AVFilterGraph @ 0x7209dfec40] No such filter: 'anull'
E/mobile-ffmpeg: Error reinitializing filters!
E/mobile-ffmpeg: Failed to inject frame into filter network: Invalid argument
E/mobile-ffmpeg: Error while processing the decoded data for stream #0:0
I/mobile-ffmpeg: Conversion failed!


  


  Does anyone know what I'm missing or another config to build a minimal size binary for this.
Any help is highly appreciated !