At Wed, 18 Oct 2006 16:53:09 -0700, Daniel Yek wrote: > > Hi, > > First of all, thanks for the previous responses that I got. All that was > very helpful. More questions here... > > What is the rational behind ALSA's PCM multichannel playback channel > assignment? ALSA appears to be using the following channel assignment: > > 5.1 Channels Channel Assignment: > 0: Front left > 1: Front right > 2: Rear Left > 3: Rear Right > 4. Center > 5. LFE > > Is this the only format ALSA supported? Yes. > Why/how it was selected in the > beginning? (Just curious about the history...) Hm, I also don't remember correctly why. I thought it's because of consistency between 4.0 and 5.1 setup. The rear offset is identical in both cases. > I think (not sure, really) the channel assignment for Windows (if it is > really one standard there) is: > 0: Front left > 1: Front right > 2: Center > 3: LFE > 4. Rear Left > 5. Rear Right Yes, for 5.1. Some AC97 codecs follow this order, and currently we do re-routing in alsa-lib because of that. > I haven't investigated AC3 (Dolby Digital) yet, anybody knows if there is a > format for channel assignment there? FL/C/FR/RL/RR/LFE, if I remember correctly. > I'm looking if there is a solution (application API) provided by ALSA to do > channel-mapping. If there is one, I can just ask ALSA to do the > "heavy-lifting" of swapping the surround sound channels. If not, I'll > iterate through the PCM data, mapping the channels to the format expected > by ALSA. Currently, there is no setup API for multi-channel binding. The channels are statically defined as FL/FR/RL/RR/C/LFE. It'd be of course nice to have an API for multi-channel binding. We can define either a read-only or a read-write API, namely, 1. The driver provides a channel mapping information for multi-channel device 2. Apps can change channel bindings dynamically as they like In each case, we can keep the original FL/FR/RL/RR/C/LFE order as a fallback so that old apps still run without modification. If you have any API proposal, please let us know. Takashi ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-devel
