AudioMixer uses downmix effect for multichannel content

In the AudioMixer structure associated with each track, add an object
  that acts as the buffer provider when the track has more than two
  channels of input in the mixer. This object, DownmixerBufferProvider,
  gets audio from the actual buffer provider of the track, and applies
  a downmix effect on it.
The downmix effect is created and configured when the track gets
  created in AudioFlinger, which causes AudioMixer::getTrackName()
  to be called with the new track's channel mask. It is released
  when the track is disabled in the mixer.

Change-Id: I05281ed5f61bef663a8af7ca7d5ceac3517c82db

1 files changed, 36 insertions, 3 deletions

diff --git a/services/audioflinger/AudioMixer.h b/services/audioflinger/AudioMixer.h
index 856450c..a04fe95 100644
--- a/services/audioflinger/AudioMixer.h
+++ b/services/audioflinger/AudioMixer.h
@@ -21,9 +21,14 @@
 #include <stdint.h>
 #include <sys/types.h>
 
+#include <utils/threads.h>
+
 #include "AudioBufferProvider.h"
 #include "AudioResampler.h"
 
+#include <audio_effects/effect_downmix.h>
+#include <system/audio.h>
+
 namespace android {
 
 // ----------------------------------------------------------------------------
@@ -37,7 +42,10 @@ public:
     /*virtual*/             ~AudioMixer();  // non-virtual saves a v-table, restore if sub-classed
 
     static const uint32_t MAX_NUM_TRACKS = 32;
+    // maximum number of channels supported by the mixer
     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;
 
     static const uint16_t UNITY_GAIN = 0x1000;
 
@@ -60,6 +68,7 @@ public:
         FORMAT          = 0x4001,
         MAIN_BUFFER     = 0x4002,
         AUX_BUFFER      = 0x4003,
+        DOWNMIX_TYPE    = 0X4004,
         // for target RESAMPLE
         SAMPLE_RATE     = 0x4100,
         RESET           = 0x4101,
@@ -94,7 +103,7 @@ public:
 private:
 
     enum {
-        NEEDS_CHANNEL_COUNT__MASK   = 0x00000003,
+        NEEDS_CHANNEL_COUNT__MASK   = 0x00000007,
         NEEDS_FORMAT__MASK          = 0x000000F0,
         NEEDS_MUTE__MASK            = 0x00000100,
         NEEDS_RESAMPLE__MASK        = 0x00001000,
@@ -119,6 +128,7 @@ private:
 
     struct state_t;
     struct track_t;
+    class DownmixerBufferProvider;
 
     typedef void (*hook_t)(track_t* t, int32_t* output, size_t numOutFrames, int32_t* temp, int32_t* aux);
     static const int BLOCKSIZE = 16; // 4 cache lines
@@ -147,8 +157,10 @@ private:
         uint8_t     channelCount;   // 1 or 2, redundant with (needs & NEEDS_CHANNEL_COUNT__MASK)
         uint8_t     format;         // always 16
         uint16_t    enabled;        // actually bool
-        uint32_t    channelMask;    // currently under-used
+        audio_channel_mask_t channelMask;
 
+        // actual buffer provider used by the track hooks, see DownmixerBufferProvider below
+        //  for how the Track buffer provider is wrapped by another one when dowmixing is required
         AudioBufferProvider*                bufferProvider;
 
         // 16-byte boundary
@@ -169,7 +181,9 @@ private:
 
         uint64_t    localTimeFreq;
 
-        int64_t     padding;
+        DownmixerBufferProvider* downmixerBufferProvider; // 4 bytes
+
+        int32_t     padding;
 
         // 16-byte boundary
 
@@ -194,6 +208,19 @@ private:
         track_t         tracks[MAX_NUM_TRACKS]; __attribute__((aligned(32)));
     };
 
+    // AudioBufferProvider that wraps a track AudioBufferProvider by a call to a downmix effect
+    class DownmixerBufferProvider : public AudioBufferProvider {
+    public:
+        virtual status_t getNextBuffer(Buffer* buffer, int64_t pts);
+        virtual void releaseBuffer(Buffer* buffer);
+        DownmixerBufferProvider();
+        virtual ~DownmixerBufferProvider();
+
+        AudioBufferProvider* mTrackBufferProvider;
+        effect_handle_t    mDownmixHandle;
+        effect_config_t    mDownmixConfig;
+    };
+
     // bitmask of allocated track names, where bit 0 corresponds to TRACK0 etc.
     uint32_t        mTrackNames;
 
@@ -205,7 +232,13 @@ private:
 
     state_t         mState __attribute__((aligned(32)));
 
+    // effect descriptor for the downmixer used by the mixer
+    static effect_descriptor_t dwnmFxDesc;
+    // indicates whether a downmix effect has been found and is usable by this mixer
+    static bool                isMultichannelCapable;
+
     void invalidateState(uint32_t mask);
+    static status_t prepareTrackForDownmix(track_t* pTrack, int trackNum);
 
     static void track__genericResample(track_t* t, int32_t* out, size_t numFrames, int32_t* temp, int32_t* aux);
     static void track__nop(track_t* t, int32_t* out, size_t numFrames, int32_t* temp, int32_t* aux);