Posted by Xerxes Rånby on Mar 14, 2014; 3:45pm
URL: https://forum.jogamp.org/playing-audio-from-an-AVI-file-tp4031894p4031901.html

2014-03-14 15:23, TheLittleP [via jogamp] skrev:
> hiya,
>
> how can I tell how the audio buffer is encoded?? I have spent hours digging around trying to unravel this.
>
> The details of the audio on the AVI is LINEAR, 8 bit mono - I was hoping the Source could play the raw chunk buffer data but it cant. there isn't any information on how the audio buffer is encoded, or I don't know how to find out.
>
> It seems WAVLoader and WAVData simply pass the raw buffer of the WAV InputStream to the Source and it plays.

WAVLoader looks for the WAVEfmt header where channels, sample-rate, bytes per second and sample size is stored. WAVLoader currently only support uncompressed WAVE files.
http://jogamp.org/git/?p=joal.git;a=blob;f=src/java/com/jogamp/openal/util/WAVLoader.java;hb=HEAD#l131

Is quite easy to pass raw data from a file to the sound-card if the audio format is known.
WAVLoader  is used by the ALut.alutLoadWAVFile to load simple wav files for the JOAL-demos lessions.
http://jogamp.org/joal-demos/www/devmaster/lesson3.html
http://jogamp.org/joal-demos/www/

>
> I will keep digging through the source code of GLMediaPlayer to try and find out how it detects the encode and what it does to decode but I thought I might ask the forum in case anyone can explain and save me hours :)
>
> many thanks
> P

GLMediaPlayer is using the FFMPEGMediaPlayer backend on desktop JogAmp systems.

By using libffmpeg/libav the audo format auto-detection is handled by libffmpeg/libav.
We can then tell how the audio buffer is encoded by simply asking the AVCodecContext that belong to the ffmpeg/libav audio decoder.

I recommend you to take a look at the ffmpeg tutorials at dranger.com
http://dranger.com/ffmpeg/tutorial03.html - Tutorial 03: Playing Sound
http://dranger.com/ffmpeg/data.html#AVCodecContext

The jogamp FFMPEGMediaPlayer backend code work quite similar to this tutorial,
you can find the audio buffer detection code inside src/jogl/native/libav/ffmpeg_impl_template.c here:
http://jogamp.org/git/?p=jogl.git;a=blob;f=src/jogl/native/libav/ffmpeg_impl_template.c;hb=HEAD#l872

We then check the AudioSink (usually JOAL ALAudioSink) if the audio format is supported by the sound-card using FFMPEGMediaPlayer.isAudioFormatSupported:
http://jogamp.org/git/?p=jogl.git;a=blob;f=src/jogl/classes/jogamp/opengl/util/av/impl/FFMPEGMediaPlayer.java;hb=HEAD#l451

For situations when the decoded audio-buffer format do not match any of the sound cards audio format then we can then ask libav/libffmpeg to re-sample all audio to match the sound cards audio format.
This fallback happens inside ffmpeg_impl_template.c using SWRESAMPLE here:
http://jogamp.org/git/?p=jogl.git;a=blob;f=src/jogl/native/libav/ffmpeg_impl_template.c;hb=HEAD#l971

Cheers
Xerxes