On Wed, 2016-04-27 at 16:53 +0200, Nicole Færber wrote: > Hello, > > I know this has been a topic several times now. I searched the > mailinglist archives, FAQ, current GIT and other internet resources for > a practical way with current versions of BlueZ5 and Pulse Audio but it > seems that most proposed patches have been dropped, am I correct with > this assessment? > > My personal goal would be to have a mode to playback AAC content to a > paired and connected A2DP device capable of A2DP-AAC - in my case a > Parrot Zik2.0. If such a way already exists I would be really happy for > an advice on how to actually use it, e.g. using paplay? > > If such a mode does not yet exist are there plans to implement other > codecs? At least as pass-through? What is needed? Is it already being > worked on? Can I give a hand? As usual time is limited and my knowledge > on A2DP and especially Pulse Audio is limited but I am willing to help. Compressed audio passthrough with bluetooth is not supported. I think the feature would be welcome, though. I'm not aware of anyone working on it. We already support compressed passthrough with alsa, so it's not necessary to start from absolute scratch. Alsa wants compressed audio wrapped in "IEC 61937" encapsulation, and that format also makes it easier for pulseaudio to deal with the data, because the encapsulation makes it possible to convert between number of bytes and time (that is, a certain number of bytes always corresponds to the same amount of time, which isn't true with plain AAC audio). For that reason we require applications to do the encapsulation, so pulseaudio doesn't have to do any changes to the data. I suppose bluetooth doesn't use the IEC 61937 encapsulation, so the question arises if we should use it in pulseaudio when doing passthrough with bluetooth. I think it would make sense to use encapsulation at least in the initial implementation, because that would then retain the nice property that we don't have to understand anything about the AAC format as such. The bluetooth module would then have to do the unpacking of the AAC data from the IEC 61937 encapsulation, which hopefully is reasonably straightforward. -- Tanu
