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Commit ed08fbe1 authored by Shuzhen Wang's avatar Shuzhen Wang
Browse files

Camera: reset presentation timestamp more aggressively 

On some platforms, VSYNC may run at a slightly lower rate
than camera output. With the current approach, the selected
timeline index may keep increase until it reaches max value,
resulting in long latency.

Address this by:
- Only use up to the first 3 expected presentation time.
- Use a bias factor which decreases the minimum presentation
  interval as the timeline index increases.
- Reset presentation time as soon as capture intervals exceed
  1.5 * 33ms.

Test: Run GoogleCamera at 24, 30, and 60fps and analyze frame drop rate
Test: Run camcorder preview/record for 10 iterations and observe preview
Bug: 236707639
Change-Id: Iabd4f7b17a6ee1eb6772fbb943c8800f48a40869
parent 34a5e28c

services/camera/libcameraservice/device3/Camera3OutputStream.cpp

+15 −4
Original line number Diff line number Diff line
@@ -1432,16 +1432,27 @@ nsecs_t Camera3OutputStream::syncTimestampToDisplayLocked(nsecs_t t) { 
    int minVsyncs = (mMinExpectedDuration - vsyncEventData.frameInterval / 2) /

            vsyncEventData.frameInterval;

    if (minVsyncs < 0) minVsyncs = 0;

    nsecs_t minInterval = minVsyncs * vsyncEventData.frameInterval + kTimelineThresholdNs;

    // Find best timestamp in the vsync timeline:

    nsecs_t minInterval = minVsyncs * vsyncEventData.frameInterval;

    // Find best timestamp in the vsync timelines:

    // - Only use at most 3 timelines to avoid long latency

    // - closest to the ideal present time,

    // - deadline timestamp is greater than the current time, and

    // - the candidate present time is at least minInterval in the future

    //   compared to last present time.

    for (const auto& vsyncTime : vsyncEventData.frameTimelines) {

    int maxTimelines = std::min(kMaxTimelines, (int)VsyncEventData::kFrameTimelinesLength);

    float biasForShortDelay = 1.0f;

    for (int i = 0; i < maxTimelines; i ++) {

        const auto& vsyncTime = vsyncEventData.frameTimelines[i];

        if (minVsyncs > 0) {

            // Bias towards using smaller timeline index:

            //   i = 0:                bias = 1

            //   i = maxTimelines-1:   bias = -1

            biasForShortDelay = 1.0 - 2.0 * i / (maxTimelines - 1);

        }

        if (std::abs(vsyncTime.expectedPresentationTime - idealPresentT) < minDiff &&

                vsyncTime.deadlineTimestamp >= currentTime &&

                vsyncTime.expectedPresentationTime > mLastPresentTime + minInterval) {

                vsyncTime.expectedPresentationTime >

                mLastPresentTime + minInterval + biasForShortDelay * kTimelineThresholdNs) {

            expectedPresentT = vsyncTime.expectedPresentationTime;

            minDiff = std::abs(vsyncTime.expectedPresentationTime - idealPresentT);

        }

services/camera/libcameraservice/device3/Camera3OutputStream.h

+2 −1
Original line number Diff line number Diff line
@@ -421,9 +421,10 @@ class Camera3OutputStream : 
    nsecs_t mLastPresentTime = 0;

    nsecs_t mCaptureToPresentOffset = 0;

    static constexpr size_t kDisplaySyncExtraBuffer = 2;

    static constexpr nsecs_t kSpacingResetIntervalNs = 1000000000LL; // 1 second

    static constexpr nsecs_t kSpacingResetIntervalNs = 50000000LL; // 50 millisecond

    static constexpr nsecs_t kTimelineThresholdNs = 1000000LL; // 1 millisecond

    static constexpr float kMaxIntervalRatioDeviation = 0.05f;

    static constexpr int kMaxTimelines = 3;

    nsecs_t syncTimestampToDisplayLocked(nsecs_t t);



    // Re-space frames by delaying queueBuffer so that frame delivery has