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先写结论:是安卓高版本上视频在暂停播放处理时加上了audio offload超时机制【降低系统功耗】优化功能导致的,offload该处理是使用音频硬解码,不是软解,其音频解码速度更快,而在PAUSE暂停时设置超时是为了降低功耗提升系统性能。
跳帧【回退几秒】原因:是重新执行了seek操作,而该操作在安卓原生播放器中不支持seek到非关键帧。
而之所以只有某些视频会出现比较明显的回退几秒现象,是由于该视频中视频数据GOP时长问题即视频编码问题,如若该视频在10秒时是一个关键帧,而之后是25秒后才是关键帧,因此结合安卓原生播放器seek到关键帧的处理,在播放进度在10秒到25秒之间暂停3秒后就会出现该bug现象产生。
备注:若是用户直接快进seek到这个非关键帧时间段内,也会有该问题,但该问题在安卓原生播放器实现目前不考虑优化的。
该3秒延迟值可以通过系统构建mk配置文件中设置的系统属性值进行修改,
在【vendor/qcom/opensource/audio-hal/primary-hal/configs/平台名/平台名.mk】中配置的,
属性值名称为【“audio.sys.offload.pstimeout.secs”】,目前系统设置为3秒。
目前考虑的可行优化方案:
1、去掉offload功能;【不推荐】 ===》可通过系统属性配置去关闭
2、将超时时长3秒扩大到10秒后等; ===》可通过系统属性配置去修改
3、修改安卓底层解码输出端让其支持seek到非关键帧;
代码分析过程:【android 10.0版本】
1、暂停流程最终会调用到NuPlayer中的该方法:
// [frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp]
void NuPlayer::Renderer::onPause() {
if (mPaused) {
return;
}
{
Mutex::Autolock autoLock(mLock);
// we do not increment audio drain generation so that we fill audio buffer during pause.
// video输出标识位增加1
++mVideoDrainGeneration;
prepareForMediaRenderingStart_l();
// 置为暂停状态
mPaused = true;
mMediaClock->setPlaybackRate(0.0);
}
// 将音视频输出标志设置为false
mDrainAudioQueuePending = false;
mDrainVideoQueuePending = false;
mVideoRenderingStarted = false; // force-notify NOTE_INFO MEDIA_INFO_RENDERING_START after resume
// 通知AudioSink暂停处理
// Note: audio data may not have been decoded, and the AudioSink may not be opened.
mAudioSink->pause();
// 关键点:Audio offload关闭Audio相关加载模块的暂停超时流程处理
// 该功能就是导致3秒后恢复播放异常原因
// 见第2小节分析
startAudioOffloadPauseTimeout();
ALOGV("now paused audio queue has %zu entries, video has %zu entries",
mAudioQueue.size(), mVideoQueue.size());
}
2、startAudioOffloadPauseTimeout实现分析:
// [frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp]
void NuPlayer::Renderer::startAudioOffloadPauseTimeout() {
if (offloadingAudio()) {
// 若支持offload mode模式
// 该值为系统属性值,系统默认为3秒,最大值为10秒【kOffloadPauseMaxUs】
int64_t pauseTimeOutDuration = property_get_int64(
"audio.sys.offload.pstimeout.secs",(kOffloadPauseMaxUs/1000000)/*default*/);
mWakeLock->acquire();
// 发送一个【kWhatAudioOffloadPauseTimeout】超时消息
// 见下面的分析
sp<AMessage> msg = new AMessage(kWhatAudioOffloadPauseTimeout, this);
msg->setInt32("drainGeneration", mAudioOffloadPauseTimeoutGeneration);
msg->post(pauseTimeOutDuration*1000000);
}
}
// [frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp]
void NuPlayer::Renderer::onMessageReceived(const sp<AMessage> &msg) {
switch(){
case kWhatAudioOffloadPauseTimeout:
{
int32_t generation;
CHECK(msg->findInt32("drainGeneration", &generation));
if (generation != mAudioOffloadPauseTimeoutGeneration) {
// 若时间到之后发现当前offload超时事件记录发生变化则跳过该处理,如3秒内进行了恢复播放
break;
}
ALOGV("Audio Offload tear down due to pause timeout.");
// 见下面的分析
onAudioTearDown(kDueToTimeout);
mWakeLock->release();
break;
}
}
}
// [frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.cpp]
void NuPlayer::Renderer::onAudioTearDown(AudioTearDownReason reason) {
if (mAudioTornDown) {
return;
}
// TimeoutWhenPaused is only for offload mode.
if (reason == kDueToTimeout && !offloadingAudio()) {
return;
}
mAudioTornDown = true;
int64_t currentPositionUs;
sp<AMessage> notify = mNotify->dup();
if (getCurrentPosition(¤tPositionUs) == OK) {
// 将当前播放时间点发送过去
notify->setInt64("positionUs", currentPositionUs);
}
mAudioSink->stop();
mAudioSink->flush();
notify->setInt32("what", kWhatAudioTearDown);
notify->setInt32("reason", reason);
// 给NuPlayer模块发送【kWhatAudioTearDown】通知
// 见下面的分析
notify->post();
}
// [frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayer.cpp]
void NuPlayer::onMessageReceived(const sp<AMessage> &msg) {
switch (msg->what()) {
case kWhatRendererNotify:
{
int32_t requesterGeneration = mRendererGeneration - 1;
CHECK(msg->findInt32("generation", &requesterGeneration));
if (requesterGeneration != mRendererGeneration) {
ALOGV("got message from old renderer, generation(%d:%d)",
requesterGeneration, mRendererGeneration);
return;
}
int32_t what;
CHECK(msg->findInt32("what", &what));
if (what == Renderer::kWhatEOS) {
// ... 省略部分代码
} else if (what == Renderer::kWhatAudioTearDown) {
int32_t reason;
CHECK(msg->findInt32("reason", &reason));
ALOGV("Tear down audio with reason %d.", reason);
if (reason == Renderer::kDueToTimeout && !(mPaused && mOffloadAudio)) {
// TimeoutWhenPaused is only for offload mode.
ALOGW("Received a stale message for teardown, mPaused(%d), mOffloadAudio(%d)",
mPaused, mOffloadAudio);
break;
}
// 获取当前播放时间点
int64_t positionUs;
if (!msg->findInt64("positionUs", &positionUs)) {
positionUs = mPreviousSeekTimeUs;
}
// 重启audio相关模块,此时reason值为kDueToTimeout
// 见下面到的分析
restartAudio(
positionUs, reason == Renderer::kForceNonOffload /* forceNonOffload */,
reason != Renderer::kDueToTimeout /* needsToCreateAudioDecoder */);
}
break;
}
}
}
// [frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayer.cpp]
void NuPlayer::restartAudio(
int64_t currentPositionUs, bool forceNonOffload, bool needsToCreateAudioDecoder) {
ALOGD("restartAudio timeUs(%lld), dontOffload(%d), createDecoder(%d)",
(long long)currentPositionUs, forceNonOffload, needsToCreateAudioDecoder);
if (mAudioDecoder != NULL) {
mAudioDecoder->pause();
Mutex::Autolock autoLock(mDecoderLock);
mAudioDecoder.clear();
mAudioDecoderError = false;
++mAudioDecoderGeneration;
}
if (mFlushingAudio == FLUSHING_DECODER) {
mFlushComplete[1 /* audio */][1 /* isDecoder */] = true;
mFlushingAudio = FLUSHED;
finishFlushIfPossible();
} else if (mFlushingAudio == FLUSHING_DECODER_SHUTDOWN
|| mFlushingAudio == SHUTTING_DOWN_DECODER) {
mFlushComplete[1 /* audio */][1 /* isDecoder */] = true;
mFlushingAudio = SHUT_DOWN;
finishFlushIfPossible();
needsToCreateAudioDecoder = false;
}
if (mRenderer == NULL) {
return;
}
closeAudioSink();
mRenderer->flush(true /* audio */, false /* notifyComplete */);
if (mVideoDecoder != NULL) {
// 此处就是关键处理处
// 会记录三个延迟操作放入list操作表中,然后调用processDeferredActions取出操作指令去执行
// flush video data请求操作
mDeferredActions.push_back(
new FlushDecoderAction(FLUSH_CMD_NONE /* audio */,
FLUSH_CMD_FLUSH /* video */));
// seek video请求操作
mDeferredActions.push_back(
new SeekAction(currentPositionUs,
MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC /* mode */));
// After a flush without shutdown, decoder is paused.
// Don't resume it until source seek is done, otherwise it could
// start pulling stale data too soon.
// 然后进行恢复video视频位置操作,
// 但是由于前面进行了flush和seek操作,导致resume seek的position时
// 会去寻找当前seek时间点前的关键帧【安卓底层NuPlayer不支持seek到非关键帧】,
// 因此最终导致了该问题的产生
mDeferredActions.push_back(new ResumeDecoderAction(false));
processDeferredActions();
} else {
performSeek(currentPositionUs, MediaPlayerSeekMode::SEEK_PREVIOUS_SYNC /* mode */);
}
if (forceNonOffload) {
mRenderer->signalDisableOffloadAudio();
mOffloadAudio = false;
}
if (needsToCreateAudioDecoder) {
mDeferredActions.push_back(
new InstantiateDecoderAction(true /* audio */, &mAudioDecoder, !forceNonOffload));
}
processDeferredActions();
}
// [frameworks/av/media/libmediaplayerservice/nuplayer/NuPlayer.cpp]
// 取出操作指令去执行
void NuPlayer::processDeferredActions() {
while (!mDeferredActions.empty()) {
// We won't execute any deferred actions until we're no longer in
// an intermediate state, i.e. one more more decoders are currently
// flushing or shutting down.
if (mFlushingAudio != NONE || mFlushingVideo != NONE) {
// We're currently flushing, postpone the reset until that's
// completed.
ALOGV("postponing action mFlushingAudio=%d, mFlushingVideo=%d",
mFlushingAudio, mFlushingVideo);
break;
}
sp<Action> action = *mDeferredActions.begin();
mDeferredActions.erase(mDeferredActions.begin());
action->execute(this);
}
}
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