Hi Glenn, Thanks for your reply, it's very helpful and confirms most of the things I've discovered in my investigation.
As a short followup question, where can I read more (either documents or source) about deep buffers? I enabled logging and added some custom log messages in AudioFlinger::PlaybackThread::threadLoop_write(), and I see that it writes to two different sinks depending on the application. One of them (the "normal sink") writes frames of audio depending on how I configure AudioFlinger, and the other one writes to an AudioStreamOut (HAL object) directly. Whenever the latter happens, I also see messages about offloading printed. Is this in any way related to deep buffers or fast/normal mixer selection? On Thursday, March 6, 2014 7:10:13 AM UTC-8, Glenn Kasten wrote: > > See attached diagram "Audio playback architecture.pdf". > This shows 3 major paths that audio can be played out, > however these are not the only paths. > > 1. Low latency tracks are mixed directly by fast mixer. > They have attenuation applied, but no resampling or app processor effects. > > 2. Normal latency tracks are mixed by normal mixer, > and in addition to attenuation can have optional resampling > or app processor effects applied. Both of the latter can use > significant CPU time, and may be bursty in CPU consumption, > thus this is why they are limited to normal tracks. > The output of normal mixer is a single fast track (via a memory pipe), > which then is treated as (1) above by fast mixer. > > 3. Deep buffer tracks, used for music playback with screen off, > go through a similar path as #2 but without the fast mixer part. > After the mix is done, it is written directly to HAL. > > There are other paths but they are less relevant to your question. > > So to answer your question: no there is no single point. > If you're applying CPU-intensive processing, I would recommed > adding them to the normal mixer path used for #2 and #3. > Avoid adding them to fast mixer as this will likely cause > performance problems for lower latency tracks. > > > On Wednesday, March 5, 2014 6:20:02 PM UTC-8, AudioLinger wrote: >> >> Hi all, >> >> I've been reading through AudioFlinger and audio hardware code looking >> for the place where all audio from all tracks and sessions comes together. >> My initial guess was the audio mixer, but there are now two audio mixers >> (the normal one and the FastMixer). When looking at the ssize_t >> AudioFlinger::PlaybackThread::threadLoop_write() method inside >> frameworks/av/services/audioflinger/Threads.cpp, depending on existence of >> a "normal sink" we either process audio through a mixer or, if I understand >> it correctly, send it directly to the hardware to take care of. My goal is >> to be able to process all audio (except phone call and other such special >> things) that the device outputs. The above mentioned method was my best >> guess, but even at that point it splits into different mixing strategies. >> >> Any pointers? >> > -- -- unsubscribe: android-porting+unsubscr...@googlegroups.com website: http://groups.google.com/group/android-porting --- You received this message because you are subscribed to the Google Groups "android-porting" group. To unsubscribe from this group and stop receiving emails from it, send an email to android-porting+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
