Re: Playing 5.1 sound on a stereo device with OpenAL Soft

On Friday, November 05, 2010 1:59:43 am Martin Lambers wrote:
> You're right, it is indeed an ffmpeg problem. Some audio streams are
> apparently *not* decoded to signed 16 bit sample formats. The ffplay
> player contains code to convert sample formats in this case, but uses an
> internal ffmpeg API for this purpose that is not part of the installed
> header files. So, no luck for alffmpeg and my project...

Seems ffmpeg was changed (again). When I originally wrote the code, 
avcodec_decode_audio2 guaranteed writing samples as signed 16-bit PCM, hence 
why the function takes int16_t* for output samples. But now it seems the 
AVCodecContext contains a sample_fmt field. And indeed, the WMA codec outputs 
32-bit float samples. This is easy enough to support with AL_EXT_FLOAT32, 
though 32-bit int and double sample formats would need conversion (double 
could work with AL_EXT_DOUBLE, but there's no multi-channel support for it).

This is one of the biggest problems I've found with using ffmpeg. It regularly 
breaks backwards compatibility, so you need to pick a specific version and 
stick with it. GStreamer is nicer for streaming playback (especially with an 
OpenAL sink <https://bugzilla.gnome.org/show_bug.cgi?id=615615> to integrate 
it with the rest of the OpenAL app), although it's not so nice for general 
decode-to-buffer functionality.
_______________________________________________
Openal mailing list
[email protected]
http://opensource.creative.com/mailman/listinfo/openal