On Mon, 25 Oct 2010 09:50:19 -0400 Paul Braman <bramankp@xxxxxxxxx> wrote: > I'll assume I want to read in blocks of 1536 bytes-at-a-time as long > as ALSA is properly synchronizing to the S/PDIF frame and giving me > aligned blocks. Is this an assumption I can make? Probably not. I recently thought I would be clever and decode my external AC3 source in software without buying an expensive home theatre system but I found out the hard way that this generally isn't possible. You can get away with a little jitter when dealing with PCM but AC3 just can't tolerate it cleanly enough. You end up with short bursts of noise every couple of seconds. If you want to try it for yourself, it's as simple as... arecord -Dspdif -f dat -t raw | spdifextract | ac3dec -6 spdifextract is a small program you can get from here... http://forums.gentoo.org/viewtopic-p-4472816.html#4472816 I spoke to the original author of the code and he never managed to work around this problem either. Simply adjusting the buffer or period size doesn't help because the data has already been lost by this point. Apparently a PLL is needed to synchronise the clock frequency but I haven't been able to determine whether any sound cards out there have these at all. I've heard of some Creative cards having on-board AC3 decoders but I think this may have simply been for DVDs being played on the machine itself, not for external sources. James ------------------------------------------------------------------------------ Nokia and AT&T present the 2010 Calling All Innovators-North America contest Create new apps & games for the Nokia N8 for consumers in U.S. and Canada $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store http://p.sf.net/sfu/nokia-dev2dev _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
