Document AudioMixer hard-coded limits

Change-Id: I83ea8bed375f251260945db788bdb5f280dba12d

2 files changed, 13 insertions, 0 deletions

diff --git a/services/audioflinger/AudioMixer.cpp b/services/audioflinger/AudioMixer.cpp
index e652d14..a4ed445 100644
--- a/services/audioflinger/AudioMixer.cpp
+++ b/services/audioflinger/AudioMixer.cpp
@@ -106,6 +106,12 @@ AudioMixer::AudioMixer(size_t frameCount, uint32_t sampleRate, uint32_t maxNumTr
     ALOG_ASSERT(maxNumTracks <= MAX_NUM_TRACKS, "maxNumTracks %u > MAX_NUM_TRACKS %u",
             maxNumTracks, MAX_NUM_TRACKS);
 
+    // AudioMixer is not yet capable of more than 32 active track inputs
+    ALOG_ASSERT(32 >= MAX_NUM_TRACKS, "bad MAX_NUM_TRACKS %d", MAX_NUM_TRACKS);
+
+    // AudioMixer is not yet capable of multi-channel output beyond stereo
+    ALOG_ASSERT(2 == MAX_NUM_CHANNELS, "bad MAX_NUM_CHANNELS %d", MAX_NUM_CHANNELS);
+
     LocalClock lc;
 
     pthread_once(&sOnceControl, &sInitRoutine);
diff --git a/services/audioflinger/AudioMixer.h b/services/audioflinger/AudioMixer.h
index dc468ff..e60a298 100644
--- a/services/audioflinger/AudioMixer.h
+++ b/services/audioflinger/AudioMixer.h
@@ -41,8 +41,15 @@ public:
 
     /*virtual*/             ~AudioMixer();  // non-virtual saves a v-table, restore if sub-classed
 
+
+    // This mixer has a hard-coded upper limit of 32 active track inputs.
+    // Adding support for > 32 tracks would require more than simply changing this value.
     static const uint32_t MAX_NUM_TRACKS = 32;
     // maximum number of channels supported by the mixer
+
+    // This mixer has a hard-coded upper limit of 2 channels for output.
+    // There is support for > 2 channel tracks down-mixed to 2 channel output via a down-mix effect.
+    // Adding support for > 2 channel output would require more than simply changing this value.
     static const uint32_t MAX_NUM_CHANNELS = 2;
     // maximum number of channels supported for the content
     static const uint32_t MAX_NUM_CHANNELS_TO_DOWNMIX = 8;