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Commit 4adcede0 authored by Glenn Kasten's avatar Glenn Kasten
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Reduce video frame drop rate 

The video playback engine depends on having relatively precise audio
progress updates for its A/V sync and frame drop calculations.  For small
audio HAL buffer sizes, this was not a problem, but when the HAL buffer
size was > 12 ms, the normal mix buffer size became > 24 ms and this
then caused video problems.  The new formula tries to keep the normal
mix buffer size within a closer tolerance of 20 ms to 24 ms.

Also use consistent term: multiplier instead of multiple.

Bug: 6479613
Change-Id: I903bad74461908e8c8f0a61e99ab5e24d5c44433
parent 09474df6

services/audioflinger/AudioFlinger.cpp

+36 −10
Original line number Diff line number Diff line
@@ -142,6 +142,8 @@ static const uint32_t kMaxThreadSleepTimeShift = 2; 


// minimum normal mix buffer size, expressed in milliseconds rather than frames

static const uint32_t kMinNormalMixBufferSizeMs = 20;

// maximum normal mix buffer size

static const uint32_t kMaxNormalMixBufferSizeMs = 24;



nsecs_t AudioFlinger::mStandbyTimeInNsecs = kDefaultStandbyTimeInNsecs;
@@ -151,9 +153,9 @@ static const enum { 
    FastMixer_Always,   // always initialize and use, even if not needed: for debugging only

                        // normal mixer multiplier is 1

    FastMixer_Static,   // initialize if needed, then use all the time if initialized,

                        // multipler is calculated based on minimum normal mixer buffer size

                        // multiplier is calculated based on min & max normal mixer buffer size

    FastMixer_Dynamic,  // initialize if needed, then use dynamically depending on track load,

                        // multipler is calculated based on minimum normal mixer buffer size

                        // multiplier is calculated based on min & max normal mixer buffer size

    // FIXME for FastMixer_Dynamic:

    //  Supporting this option will require fixing HALs that can't handle large writes.

    //  For example, one HAL implementation returns an error from a large write,
@@ -1950,18 +1952,42 @@ void AudioFlinger::PlaybackThread::readOutputParameters() 
    }



    // Calculate size of normal mix buffer relative to the HAL output buffer size

    uint32_t multiple = 1;

    double multiplier = 1.0;

    if (mType == MIXER && (kUseFastMixer == FastMixer_Static || kUseFastMixer == FastMixer_Dynamic)) {

        size_t minNormalFrameCount = (kMinNormalMixBufferSizeMs * mSampleRate) / 1000;

        multiple = (minNormalFrameCount + mFrameCount - 1) / mFrameCount;

        // force multiple to be even, for compatibility with doubling of fast tracks due to HAL SRC

        // (it would be unusual for the normal mix buffer size to not be a multiple of fast track)

        size_t maxNormalFrameCount = (kMaxNormalMixBufferSizeMs * mSampleRate) / 1000;

        // round up minimum and round down maximum to nearest 16 frames to satisfy AudioMixer

        minNormalFrameCount = (minNormalFrameCount + 15) & ~15;

        maxNormalFrameCount = maxNormalFrameCount & ~15;

        if (maxNormalFrameCount < minNormalFrameCount) {

            maxNormalFrameCount = minNormalFrameCount;

        }

        multiplier = (double) minNormalFrameCount / (double) mFrameCount;

        if (multiplier <= 1.0) {

            multiplier = 1.0;

        } else if (multiplier <= 2.0) {

            if (2 * mFrameCount <= maxNormalFrameCount) {

                multiplier = 2.0;

            } else {

                multiplier = (double) maxNormalFrameCount / (double) mFrameCount;

            }

        } else {

            // prefer an even multiplier, for compatibility with doubling of fast tracks due to HAL SRC

            // (it would be unusual for the normal mix buffer size to not be a multiple of fast

            // track, but we sometimes have to do this to satisfy the maximum frame count constraint)

            // FIXME this rounding up should not be done if no HAL SRC

        if ((multiple > 2) && (multiple & 1)) {

            ++multiple;

            uint32_t truncMult = (uint32_t) multiplier;

            if ((truncMult & 1)) {

                if ((truncMult + 1) * mFrameCount <= maxNormalFrameCount) {

                    ++truncMult;

                }

            }

            multiplier = (double) truncMult;

        }

    }

    mNormalFrameCount = multiple * mFrameCount;

    mNormalFrameCount = multiplier * mFrameCount;

    // round up to nearest 16 frames to satisfy AudioMixer

    mNormalFrameCount = (mNormalFrameCount + 15) & ~15;

    ALOGI("HAL output buffer size %u frames, normal mix buffer size %u frames", mFrameCount, mNormalFrameCount);



    // FIXME - Current mixer implementation only supports stereo output: Always