commit 0cae043f78faa7d92d145cd7021040a5f165d580
author Atneya Nair <atneya@google.com> Tue May 10 18:12:12 2022 -0400
committer Atneya Nair <atneya@google.com> Wed May 11 12:56:01 2022 -0400
tree d59b80f97c976c2525a9e92b3b801717bd40785b
parent 688cec6e7adb88f3a121ab94d5aaa9ecd9a0d312

Allow frame count regress in AudioStreamOut

AudioStreamOut attempts to detect wraparound by assuming that the
HAL frame count is monotonic, which is not true wrt gapless offload
tracks. When a non-monotonic update is detected, we freeze the fw
side framecount, rather than updating. The exception is when we
are notified that framecount will reset (e.g. flush()).

Since the notification that we are transitioning can occur arbitrarily
in advance from the HAL, upon presentationComplete for a offload stream,
we notify AudioStreamOut that we expect an upcoming framecount reset
from the HAL.
Then, we do not suppress the next detected non-monotonic sample, and
appropriately decrease the uint64 mRenderPosition.

Test: offloadAudioTrackPlayer manual test app (exoplayer test in
google3)

Bug: 191950723
Change-Id: I6060d0a9750783c2e2a7b46ce592c042d1405aa0

services/audioflinger/AudioStreamOut.cpp

diff --git a/services/audioflinger/AudioStreamOut.cpp b/services/audioflinger/AudioStreamOut.cpp
index d8565bd..65ec0e8 100644
--- a/services/audioflinger/AudioStreamOut.cpp
+++ b/services/audioflinger/AudioStreamOut.cpp
@@ -39,6 +39,7 @@
         , mRateMultiplier(1)
         , mHalFormatHasProportionalFrames(false)
         , mHalFrameSize(0)
+        , mExpectRetrograde(false)
 {
 }
 
@@ -69,8 +70,12 @@
     const uint32_t truncatedPosition = (uint32_t)mRenderPosition;
     int32_t deltaHalPosition; // initialization not needed, overwitten by __builtin_sub_overflow()
     (void) __builtin_sub_overflow(halPosition, truncatedPosition, &deltaHalPosition);
+
     if (deltaHalPosition > 0) {
         mRenderPosition += deltaHalPosition;
+    } else if (mExpectRetrograde) {
+        mExpectRetrograde = false;
+        mRenderPosition -= static_cast<uint64_t>(-deltaHalPosition);
     }
     // Scale from HAL sample rate to application rate.
     *frames = mRenderPosition / mRateMultiplier;
@@ -187,6 +192,7 @@
 int AudioStreamOut::flush()
 {
     mRenderPosition = 0;
+    mExpectRetrograde = false;
     mFramesWritten = 0;
     mFramesWrittenAtStandby = 0;
     status_t result = stream->flush();
@@ -196,6 +202,7 @@
 int AudioStreamOut::standby()
 {
     mRenderPosition = 0;
+    mExpectRetrograde = false;
     mFramesWrittenAtStandby = mFramesWritten;
     return stream->standby();
 }