Merge "Initial HLS seamless switch implementation." (52d623d4) · Commits · e / os / android_frameworks_av

media/libstagefright/httplive/LiveSession.cpp

+250 −30

Original line number	Diff line number	Diff line
		@@ -40,6 +40,8 @@
		#include <media/stagefright/MetaData.h>
		#include <media/stagefright/Utils.h>

		#include <utils/Mutex.h>

		#include <ctype.h>
		#include <openssl/aes.h>
		#include <openssl/md5.h>
		@@ -56,10 +58,14 @@ LiveSession::LiveSession(
		mHTTPDataSource(new MediaHTTP(mHTTPService->makeHTTPConnection())),
		mPrevBandwidthIndex(-1),
		mStreamMask(0),
		mNewStreamMask(0),
		mSwapMask(0),
		mCheckBandwidthGeneration(0),
		mSwitchGeneration(0),
		mLastDequeuedTimeUs(0ll),
		mRealTimeBaseUs(0ll),
		mReconfigurationInProgress(false),
		mSwitchInProgress(false),
		mDisconnectReplyID(0) {

		mStreams[kAudioIndex] = StreamItem("audio");
		@@ -68,16 +74,37 @@ LiveSession::LiveSession(

		for (size_t i = 0; i < kMaxStreams; ++i) {
		mPacketSources.add(indexToType(i), new AnotherPacketSource(NULL /* meta */));
		mPacketSources2.add(indexToType(i), new AnotherPacketSource(NULL /* meta */));
		}
		}

		LiveSession::~LiveSession() {
		}

		sp<ABuffer> LiveSession::createFormatChangeBuffer(bool swap) {
		ABuffer *discontinuity = new ABuffer(0);
		discontinuity->meta()->setInt32("discontinuity", ATSParser::DISCONTINUITY_FORMATCHANGE);
		discontinuity->meta()->setInt32("swapPacketSource", swap);
		discontinuity->meta()->setInt32("switchGeneration", mSwitchGeneration);
		discontinuity->meta()->setInt64("timeUs", -1);
		return discontinuity;
		}

		void LiveSession::swapPacketSource(StreamType stream) {
		sp<AnotherPacketSource> &aps = mPacketSources.editValueFor(stream);
		sp<AnotherPacketSource> &aps2 = mPacketSources2.editValueFor(stream);
		sp<AnotherPacketSource> tmp = aps;
		aps = aps2;
		aps2 = tmp;
		aps2->clear();
		}

		status_t LiveSession::dequeueAccessUnit(
		StreamType stream, sp<ABuffer> *accessUnit) {
		if (!(mStreamMask & stream)) {
		return UNKNOWN_ERROR;
		// return -EWOULDBLOCK to avoid halting the decoder
		// when switching between audio/video and audio only.
		return -EWOULDBLOCK;
		}

		sp<AnotherPacketSource> packetSource = mPacketSources.valueFor(stream);
		@@ -117,6 +144,25 @@ status_t LiveSession::dequeueAccessUnit(
		streamStr,
		type,
		extra == NULL ? "NULL" : extra->debugString().c_str());

		int32_t swap;
		if (type == ATSParser::DISCONTINUITY_FORMATCHANGE
		&& (*accessUnit)->meta()->findInt32("swapPacketSource", &swap)
		&& swap) {

		int32_t switchGeneration;
		CHECK((*accessUnit)->meta()->findInt32("switchGeneration", &switchGeneration));
		{
		Mutex::Autolock lock(mSwapMutex);
		if (switchGeneration == mSwitchGeneration) {
		swapPacketSource(stream);
		sp<AMessage> msg = new AMessage(kWhatSwapped, id());
		msg->setInt32("stream", stream);
		msg->setInt32("switchGeneration", switchGeneration);
		msg->post();
		}
		}
		}
		} else if (err == OK) {
		if (stream == STREAMTYPE_AUDIO \|\| stream == STREAMTYPE_VIDEO) {
		int64_t timeUs;
		@@ -138,6 +184,7 @@ status_t LiveSession::dequeueAccessUnit(
		}

		status_t LiveSession::getStreamFormat(StreamType stream, sp<AMessage> *format) {
		// No swapPacketSource race condition; called from the same thread as dequeueAccessUnit.
		if (!(mStreamMask & stream)) {
		return UNKNOWN_ERROR;
		}
		@@ -234,7 +281,12 @@ void LiveSession::onMessageReceived(const sp<AMessage> &msg) {
		if (what == PlaylistFetcher::kWhatStopped) {
		AString uri;
		CHECK(msg->findString("uri", &uri));
		mFetcherInfos.removeItem(uri);
		if (mFetcherInfos.removeItem(uri) < 0) {
		// ignore duplicated kWhatStopped messages.
		break;
		}

		tryToFinishBandwidthSwitch();
		}

		if (mContinuation != NULL) {
		@@ -270,6 +322,8 @@ void LiveSession::onMessageReceived(const sp<AMessage> &msg) {
		postPrepared(err);
		}

		cancelBandwidthSwitch();

		mPacketSources.valueFor(STREAMTYPE_AUDIO)->signalEOS(err);

		mPacketSources.valueFor(STREAMTYPE_VIDEO)->signalEOS(err);
		@@ -308,6 +362,27 @@ void LiveSession::onMessageReceived(const sp<AMessage> &msg) {
		break;
		}

		case PlaylistFetcher::kWhatStartedAt:
		{
		int32_t switchGeneration;
		CHECK(msg->findInt32("switchGeneration", &switchGeneration));

		if (switchGeneration != mSwitchGeneration) {
		break;
		}

		// Resume fetcher for the original variant; the resumed fetcher should
		// continue until the timestamps found in msg, which is stored by the
		// new fetcher to indicate where the new variant has started buffering.
		for (size_t i = 0; i < mFetcherInfos.size(); i++) {
		const FetcherInfo info = mFetcherInfos.valueAt(i);
		if (info.mToBeRemoved) {
		info.mFetcher->resumeUntilAsync(msg);
		}
		}
		break;
		}

		default:
		TRESPASS();
		}
		@@ -352,6 +427,11 @@ void LiveSession::onMessageReceived(const sp<AMessage> &msg) {
		break;
		}

		case kWhatSwapped:
		{
		onSwapped(msg);
		break;
		}
		default:
		TRESPASS();
		break;
		@@ -462,6 +542,10 @@ void LiveSession::finishDisconnect() {
		// during disconnection either.
		cancelCheckBandwidthEvent();

		// Protect mPacketSources from a swapPacketSource race condition through disconnect.
		// (finishDisconnect, onFinishDisconnect2)
		cancelBandwidthSwitch();

		for (size_t i = 0; i < mFetcherInfos.size(); ++i) {
		mFetcherInfos.valueAt(i).mFetcher->stopAsync();
		}
		@@ -501,11 +585,13 @@ sp<PlaylistFetcher> LiveSession::addFetcher(const char *uri) {

		sp<AMessage> notify = new AMessage(kWhatFetcherNotify, id());
		notify->setString("uri", uri);
		notify->setInt32("switchGeneration", mSwitchGeneration);

		FetcherInfo info;
		info.mFetcher = new PlaylistFetcher(notify, this, uri);
		info.mDurationUs = -1ll;
		info.mIsPrepared = false;
		info.mToBeRemoved = false;
		looper()->registerHandler(info.mFetcher);

		mFetcherInfos.add(uri, info);
		@@ -845,8 +931,25 @@ status_t LiveSession::selectTrack(size_t index, bool select) {
		return err;
		}

		bool LiveSession::canSwitchUp() {
		// Allow upwards bandwidth switch when a stream has buffered at least 10 seconds.
		status_t err = OK;
		for (size_t i = 0; i < mPacketSources.size(); ++i) {
		sp<AnotherPacketSource> source = mPacketSources.valueAt(i);
		int64_t dur = source->getBufferedDurationUs(&err);
		if (err == OK && dur > 10000000) {
		return true;
		}
		}
		return false;
		}

		void LiveSession::changeConfiguration(
		int64_t timeUs, size_t bandwidthIndex, bool pickTrack) {
		// Protect mPacketSources from a swapPacketSource race condition through reconfiguration.
		// (changeConfiguration, onChangeConfiguration2, onChangeConfiguration3).
		cancelBandwidthSwitch();

		CHECK(!mReconfigurationInProgress);
		mReconfigurationInProgress = true;

		@@ -862,7 +965,8 @@ void LiveSession::changeConfiguration(
		CHECK_LT(bandwidthIndex, mBandwidthItems.size());
		const BandwidthItem &item = mBandwidthItems.itemAt(bandwidthIndex);

		uint32_t streamMask = 0;
		uint32_t streamMask = 0; // streams that should be fetched by the new fetcher
		uint32_t resumeMask = 0; // streams that should be fetched by the original fetcher

		AString URIs[kMaxStreams];
		for (size_t i = 0; i < kMaxStreams; ++i) {
		@@ -880,9 +984,14 @@ void LiveSession::changeConfiguration(

		// If we're seeking all current fetchers are discarded.
		if (timeUs < 0ll) {
		for (size_t j = 0; j < kMaxStreams; ++j) {
		if ((streamMask & indexToType(j)) && uri == URIs[j]) {
		// delay fetcher removal
		discardFetcher = false;

		for (size_t j = 0; j < kMaxStreams; ++j) {
		StreamType type = indexToType(j);
		if ((streamMask & type) && uri == URIs[j]) {
		resumeMask \|= type;
		streamMask &= ~type;
		}
		}
		}
		@@ -894,8 +1003,15 @@ void LiveSession::changeConfiguration(
		}
		}

		sp<AMessage> msg = new AMessage(kWhatChangeConfiguration2, id());
		sp<AMessage> msg;
		if (timeUs < 0ll) {
		// skip onChangeConfiguration2 (decoder destruction) if switching.
		msg = new AMessage(kWhatChangeConfiguration3, id());
		} else {
		msg = new AMessage(kWhatChangeConfiguration2, id());
		}
		msg->setInt32("streamMask", streamMask);
		msg->setInt32("resumeMask", resumeMask);
		msg->setInt64("timeUs", timeUs);
		for (size_t i = 0; i < kMaxStreams; ++i) {
		if (streamMask & indexToType(i)) {
		@@ -978,11 +1094,13 @@ void LiveSession::onChangeConfiguration2(const sp<AMessage> &msg) {
		}

		void LiveSession::onChangeConfiguration3(const sp<AMessage> &msg) {
		mContinuation.clear();
		// All remaining fetchers are still suspended, the player has shutdown
		// any decoders that needed it.

		uint32_t streamMask;
		uint32_t streamMask, resumeMask;
		CHECK(msg->findInt32("streamMask", (int32_t *)&streamMask));
		CHECK(msg->findInt32("resumeMask", (int32_t *)&resumeMask));

		for (size_t i = 0; i < kMaxStreams; ++i) {
		if (streamMask & indexToType(i)) {
		@@ -991,37 +1109,39 @@ void LiveSession::onChangeConfiguration3(const sp<AMessage> &msg) {
		}

		int64_t timeUs;
		bool switching = false;
		CHECK(msg->findInt64("timeUs", &timeUs));

		if (timeUs < 0ll) {
		timeUs = mLastDequeuedTimeUs;
		switching = true;
		}
		mRealTimeBaseUs = ALooper::GetNowUs() - timeUs;

		mStreamMask = streamMask;
		mNewStreamMask = streamMask;

		// Resume all existing fetchers and assign them packet sources.
		// Of all existing fetchers:
		// * Resume fetchers that are still needed and assign them original packet sources.
		// * Mark otherwise unneeded fetchers for removal.
		ALOGV("resuming fetchers for mask 0x%08x", resumeMask);
		for (size_t i = 0; i < mFetcherInfos.size(); ++i) {
		const AString &uri = mFetcherInfos.keyAt(i);

		uint32_t resumeMask = 0;

		sp<AnotherPacketSource> sources[kMaxStreams];
		for (size_t j = 0; j < kMaxStreams; ++j) {
		if ((streamMask & indexToType(j)) && uri == mStreams[j].mUri) {
		if ((resumeMask & indexToType(j)) && uri == mStreams[j].mUri) {
		sources[j] = mPacketSources.valueFor(indexToType(j));
		resumeMask \|= indexToType(j);
		}
		}

		CHECK_NE(resumeMask, 0u);

		ALOGV("resuming fetchers for mask 0x%08x", resumeMask);

		streamMask &= ~resumeMask;

		mFetcherInfos.valueAt(i).mFetcher->startAsync(
		FetcherInfo &info = mFetcherInfos.editValueAt(i);
		if (sources[kAudioIndex] != NULL \|\| sources[kVideoIndex] != NULL
		\|\| sources[kSubtitleIndex] != NULL) {
		info.mFetcher->startAsync(
		sources[kAudioIndex], sources[kVideoIndex], sources[kSubtitleIndex]);
		} else {
		info.mToBeRemoved = true;
		}
		}

		// streamMask now only contains the types that need a new fetcher created.
		@@ -1030,6 +1150,8 @@ void LiveSession::onChangeConfiguration3(const sp<AMessage> &msg) {
		ALOGV("creating new fetchers for mask 0x%08x", streamMask);
		}

		// Find out when the original fetchers have buffered up to and start the new fetchers
		// at a later timestamp.
		for (size_t i = 0; i < kMaxStreams; i++) {
		if (!(indexToType(i) & streamMask)) {
		continue;
		@@ -1041,12 +1163,40 @@ void LiveSession::onChangeConfiguration3(const sp<AMessage> &msg) {
		sp<PlaylistFetcher> fetcher = addFetcher(uri.c_str());
		CHECK(fetcher != NULL);

		int32_t latestSeq = -1;
		int64_t latestTimeUs = 0ll;
		sp<AnotherPacketSource> sources[kMaxStreams];

		// TRICKY: looping from i as earlier streams are already removed from streamMask
		for (size_t j = i; j < kMaxStreams; ++j) {
		if ((streamMask & indexToType(j)) && uri == mStreams[j].mUri) {
		sources[j] = mPacketSources.valueFor(indexToType(j));

		if (!switching) {
		sources[j]->clear();
		} else {
		int32_t type, seq;
		int64_t srcTimeUs;
		sp<AMessage> meta = sources[j]->getLatestMeta();

		if (meta != NULL && !meta->findInt32("discontinuity", &type)) {
		CHECK(meta->findInt32("seq", &seq));
		if (seq > latestSeq) {
		latestSeq = seq;
		}
		CHECK(meta->findInt64("timeUs", &srcTimeUs));
		if (srcTimeUs > latestTimeUs) {
		latestTimeUs = srcTimeUs;
		}
		}

		sources[j] = mPacketSources2.valueFor(indexToType(j));
		sources[j]->clear();
		uint32_t extraStreams = mNewStreamMask & (~mStreamMask);
		if (extraStreams & indexToType(j)) {
		sources[j]->queueAccessUnit(createFormatChangeBuffer(/* swap = */ false));
		}
		}

		streamMask &= ~indexToType(j);
		}
		@@ -1056,7 +1206,9 @@ void LiveSession::onChangeConfiguration3(const sp<AMessage> &msg) {
		sources[kAudioIndex],
		sources[kVideoIndex],
		sources[kSubtitleIndex],
		timeUs);
		timeUs,
		latestTimeUs /* min start time(us) */,
		latestSeq >= 0 ? latestSeq + 1 : -1 /* starting sequence number hint */ );
		}

		// All fetchers have now been started, the configuration change
		@@ -1065,14 +1217,61 @@ void LiveSession::onChangeConfiguration3(const sp<AMessage> &msg) {
		scheduleCheckBandwidthEvent();

		ALOGV("XXX configuration change completed.");

		mReconfigurationInProgress = false;
		if (switching) {
		mSwitchInProgress = true;
		} else {
		mStreamMask = mNewStreamMask;
		}

		if (mDisconnectReplyID != 0) {
		finishDisconnect();
		}
		}

		void LiveSession::onSwapped(const sp<AMessage> &msg) {
		int32_t switchGeneration;
		CHECK(msg->findInt32("switchGeneration", &switchGeneration));
		if (switchGeneration != mSwitchGeneration) {
		return;
		}

		int32_t stream;
		CHECK(msg->findInt32("stream", &stream));
		mSwapMask \|= stream;
		if (mSwapMask != mStreamMask) {
		return;
		}

		// Check if new variant contains extra streams.
		uint32_t extraStreams = mNewStreamMask & (~mStreamMask);
		while (extraStreams) {
		StreamType extraStream = (StreamType) (extraStreams & ~(extraStreams - 1));
		swapPacketSource(extraStream);
		extraStreams &= ~extraStream;
		}

		tryToFinishBandwidthSwitch();
		}

		// Mark switch done when:
		// 1. all old buffers are swapped out, AND
		// 2. all old fetchers are removed.
		void LiveSession::tryToFinishBandwidthSwitch() {
		bool needToRemoveFetchers = false;
		for (size_t i = 0; i < mFetcherInfos.size(); ++i) {
		if (mFetcherInfos.valueAt(i).mToBeRemoved) {
		needToRemoveFetchers = true;
		break;
		}
		}
		if (!needToRemoveFetchers && mSwapMask == mStreamMask) {
		mStreamMask = mNewStreamMask;
		mSwitchInProgress = false;
		mSwapMask = 0;
		}
		}

		void LiveSession::scheduleCheckBandwidthEvent() {
		sp<AMessage> msg = new AMessage(kWhatCheckBandwidth, id());
		msg->setInt32("generation", mCheckBandwidthGeneration);
		@@ -1083,16 +1282,37 @@ void LiveSession::cancelCheckBandwidthEvent() {
		++mCheckBandwidthGeneration;
		}

		void LiveSession::onCheckBandwidth() {
		if (mReconfigurationInProgress) {
		scheduleCheckBandwidthEvent();
		return;
		void LiveSession::cancelBandwidthSwitch() {
		Mutex::Autolock lock(mSwapMutex);
		mSwitchGeneration++;
		mSwitchInProgress = false;
		mSwapMask = 0;
		}

		bool LiveSession::canSwitchBandwidthTo(size_t bandwidthIndex) {
		if (mReconfigurationInProgress \|\| mSwitchInProgress) {
		return false;
		}

		if (mPrevBandwidthIndex < 0) {
		return true;
		}

		if (bandwidthIndex == (size_t)mPrevBandwidthIndex) {
		return false;
		} else if (bandwidthIndex > (size_t)mPrevBandwidthIndex) {
		return canSwitchUp();
		} else {
		return true;
		}
		}

		void LiveSession::onCheckBandwidth() {
		size_t bandwidthIndex = getBandwidthIndex();
		if (mPrevBandwidthIndex < 0
		\|\| bandwidthIndex != (size_t)mPrevBandwidthIndex) {
		if (canSwitchBandwidthTo(bandwidthIndex)) {
		changeConfiguration(-1ll /* timeUs */, bandwidthIndex);
		} else {
		scheduleCheckBandwidthEvent();
		}

		// Handling the kWhatCheckBandwidth even here does _not_ automatically

media/libstagefright/httplive/LiveSession.h

+36 −0

Original line number	Diff line number	Diff line
		@@ -83,6 +83,11 @@ struct LiveSession : public AHandler {
		kWhatPreparationFailed,
		};

		// create a format-change discontinuity
		//
		// swap:
		// whether is format-change discontinuity should trigger a buffer swap
		sp<ABuffer> createFormatChangeBuffer(bool swap = true);
		protected:
		virtual ~LiveSession();

		@@ -101,6 +106,7 @@ private:
		kWhatChangeConfiguration2 = 'chC2',
		kWhatChangeConfiguration3 = 'chC3',
		kWhatFinishDisconnect2 = 'fin2',
		kWhatSwapped = 'swap',
		};

		struct BandwidthItem {
		@@ -112,6 +118,7 @@ private:
		sp<PlaylistFetcher> mFetcher;
		int64_t mDurationUs;
		bool mIsPrepared;
		bool mToBeRemoved;
		};

		struct StreamItem {
		@@ -146,9 +153,26 @@ private:
		KeyedVector<AString, FetcherInfo> mFetcherInfos;
		uint32_t mStreamMask;

		// Masks used during reconfiguration:
		// mNewStreamMask: streams in the variant playlist we're switching to;
		// we don't want to immediately overwrite the original value.
		uint32_t mNewStreamMask;

		// mSwapMask: streams that have started to playback content in the new variant playlist;
		// we use this to track reconfiguration progress.
		uint32_t mSwapMask;

		KeyedVector<StreamType, sp<AnotherPacketSource> > mPacketSources;
		// A second set of packet sources that buffer content for the variant we're switching to.
		KeyedVector<StreamType, sp<AnotherPacketSource> > mPacketSources2;

		// A mutex used to serialize two sets of events:
		// * the swapping of packet sources in dequeueAccessUnit on the player thread, AND
		// * a forced bandwidth switch termination in cancelSwitch on the live looper.
		Mutex mSwapMutex;

		int32_t mCheckBandwidthGeneration;
		int32_t mSwitchGeneration;

		size_t mContinuationCounter;
		sp<AMessage> mContinuation;
		@@ -157,6 +181,7 @@ private:
		int64_t mRealTimeBaseUs;

		bool mReconfigurationInProgress;
		bool mSwitchInProgress;
		uint32_t mDisconnectReplyID;

		sp<PlaylistFetcher> addFetcher(const char *uri);
		@@ -199,16 +224,27 @@ private:
		void onChangeConfiguration(const sp<AMessage> &msg);
		void onChangeConfiguration2(const sp<AMessage> &msg);
		void onChangeConfiguration3(const sp<AMessage> &msg);
		void onSwapped(const sp<AMessage> &msg);
		void tryToFinishBandwidthSwitch();

		void scheduleCheckBandwidthEvent();
		void cancelCheckBandwidthEvent();

		// cancelBandwidthSwitch is atomic wrt swapPacketSource; call it to prevent packet sources
		// from being swapped out on stale discontinuities while manipulating
		// mPacketSources/mPacketSources2.
		void cancelBandwidthSwitch();

		bool canSwitchBandwidthTo(size_t bandwidthIndex);
		void onCheckBandwidth();

		void finishDisconnect();

		void postPrepared(status_t err);

		void swapPacketSource(StreamType stream);
		bool canSwitchUp();

		DISALLOW_EVIL_CONSTRUCTORS(LiveSession);
		};

media/libstagefright/httplive/PlaylistFetcher.cpp

+234 −17

File changed.

Preview size limit exceeded, changes collapsed.

media/libstagefright/httplive/PlaylistFetcher.h

+21 −1

Original line number	Diff line number	Diff line
		@@ -43,6 +43,7 @@ struct PlaylistFetcher : public AHandler {
		kWhatTemporarilyDoneFetching,
		kWhatPrepared,
		kWhatPreparationFailed,
		kWhatStartedAt,
		};

		PlaylistFetcher(
		@@ -56,12 +57,16 @@ struct PlaylistFetcher : public AHandler {
		const sp<AnotherPacketSource> &audioSource,
		const sp<AnotherPacketSource> &videoSource,
		const sp<AnotherPacketSource> &subtitleSource,
		int64_t startTimeUs = -1ll);
		int64_t startTimeUs = -1ll,
		int64_t minStartTimeUs = 0ll /* start after this timestamp */,
		int32_t startSeqNumberHint = -1 /* try starting at this sequence number */);

		void pauseAsync();

		void stopAsync();

		void resumeUntilAsync(const sp<AMessage> &params);

		protected:
		virtual ~PlaylistFetcher();
		virtual void onMessageReceived(const sp<AMessage> &msg);
		@@ -76,17 +81,25 @@ private:
		kWhatPause = 'paus',
		kWhatStop = 'stop',
		kWhatMonitorQueue = 'moni',
		kWhatResumeUntil = 'rsme',
		kWhatDownloadNext = 'dlnx',
		};

		static const int64_t kMinBufferedDurationUs;
		static const int64_t kMaxMonitorDelayUs;
		static const int32_t kNumSkipFrames;

		// notifications to mSession
		sp<AMessage> mNotify;
		sp<AMessage> mStartTimeUsNotify;

		sp<LiveSession> mSession;
		AString mURI;

		uint32_t mStreamTypeMask;
		int64_t mStartTimeUs;
		int64_t mMinStartTimeUs; // start fetching no earlier than this value
		sp<AMessage> mStopParams; // message containing the latest timestamps we should fetch.

		KeyedVector<LiveSession::StreamType, sp<AnotherPacketSource> >
		mPacketSources;
		@@ -153,6 +166,9 @@ private:
		void onMonitorQueue();
		void onDownloadNext();

		// Resume a fetcher to continue until the stopping point stored in msg.
		status_t onResumeUntil(const sp<AMessage> &msg);

		status_t extractAndQueueAccessUnits(
		const sp<ABuffer> &buffer, const sp<AMessage> &itemMeta);

		@@ -165,6 +181,10 @@ private:

		void updateDuration();

		// Before resuming a fetcher in onResume, check the remaining duration is longer than that
		// returned by resumeThreshold.
		int64_t resumeThreshold(const sp<AMessage> &msg);

		DISALLOW_EVIL_CONSTRUCTORS(PlaylistFetcher);
		};