[pulseaudio-discuss] PulseAudio and AC3 passthrough

pl bossart bossart.nospam at gmail.com
Wed Jun 9 12:56:55 PDT 2010

It's been more than a year that this topic shows as 'being on the
roadmap', but for now the reality is that people bypass PulseAudio to
hear multichannel sound. I thought solving this would be a nice summer
skunkworks project while everyone is busy increasing their chances of
skin cancer.
Here's the deal: formatting an AC3 file into the required IEC format
takes about 30 lines of code, this can be done in the application that
connects to PulseAudio. Then the problem is to pass raw data
internally without applying any volume controls and with mixing
disabled. There's no issue with timing or variable bitrate since the
formatting adds headers and zero-padding to reach the non-compressed
PCM bitrate, i.e. all the bytes-to-ms conversions still apply.
I started looking into this but the volume control code is spread out
between sink-input, sink, alsa, and it's hard to figure out how to go
about this. Likewise, preventing mixing isn't self-explanatory. If
anyone has pointers on these points or is willing to contribute, let
me know.
- Pierre

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