stagefright: Fix bugs in playlist fetcher logic

1. Improve start time: start playback as soon as the target duration
or 10s was buffered.
2. Select playlist monitor time based on target duration to avoid
continuously missing the boat.
3. If "we miss the boat" we still must request a safe sequence
number (last - 3)

Change-Id: Ie99c360ac67b152ad9af19e9c6e520016f67e4e3
Signed-off-by: Lajos Molnar <lajos@google.com>
Bug: 12060952

2 files changed, 105 insertions, 29 deletions

diff --git a/media/libstagefright/httplive/PlaylistFetcher.cpp b/media/libstagefright/httplive/PlaylistFetcher.cpp
index 973b779..1754bf2 100644
--- a/media/libstagefright/httplive/PlaylistFetcher.cpp
+++ b/media/libstagefright/httplive/PlaylistFetcher.cpp
@@ -47,6 +47,7 @@ namespace android {
 
 // static
 const int64_t PlaylistFetcher::kMinBufferedDurationUs = 10000000ll;
+const int64_t PlaylistFetcher::kMaxMonitorDelayUs = 3000000ll;
 
 PlaylistFetcher::PlaylistFetcher(
         const sp<AMessage> &notify,
@@ -61,6 +62,7 @@ PlaylistFetcher::PlaylistFetcher(
       mSeqNumber(-1),
       mNumRetries(0),
       mStartup(true),
+      mPrepared(false),
       mNextPTSTimeUs(-1ll),
       mMonitorQueueGeneration(0),
       mRefreshState(INITIAL_MINIMUM_RELOAD_DELAY),
@@ -103,10 +105,16 @@ int64_t PlaylistFetcher::getSegmentStartTimeUs(int32_t seqNumber) const {
     return segmentStartUs;
 }
 
-bool PlaylistFetcher::timeToRefreshPlaylist(int64_t nowUs) const {
-    if (mPlaylist == NULL) {
+int64_t PlaylistFetcher::delayUsToRefreshPlaylist() const {
+    int64_t nowUs = ALooper::GetNowUs();
+
+    if (mPlaylist == NULL || mLastPlaylistFetchTimeUs < 0ll) {
         CHECK_EQ((int)mRefreshState, (int)INITIAL_MINIMUM_RELOAD_DELAY);
-        return true;
+        return 0ll;
+    }
+
+    if (mPlaylist->isComplete()) {
+        return (~0llu >> 1);
     }
 
     int32_t targetDurationSecs;
@@ -157,7 +165,8 @@ bool PlaylistFetcher::timeToRefreshPlaylist(int64_t nowUs) const {
             break;
     }
 
-    return mLastPlaylistFetchTimeUs + minPlaylistAgeUs <= nowUs;
+    int64_t delayUs = mLastPlaylistFetchTimeUs + minPlaylistAgeUs - nowUs;
+    return delayUs > 0ll ? delayUs : 0ll;
 }
 
 status_t PlaylistFetcher::decryptBuffer(
@@ -274,7 +283,15 @@ status_t PlaylistFetcher::decryptBuffer(
     return OK;
 }
 
-void PlaylistFetcher::postMonitorQueue(int64_t delayUs) {
+void PlaylistFetcher::postMonitorQueue(int64_t delayUs, int64_t minDelayUs) {
+    int64_t maxDelayUs = delayUsToRefreshPlaylist();
+    if (maxDelayUs < minDelayUs) {
+        maxDelayUs = minDelayUs;
+    }
+    if (delayUs > maxDelayUs) {
+        ALOGV("Need to refresh playlist in %lld", maxDelayUs);
+        delayUs = maxDelayUs;
+    }
     sp<AMessage> msg = new AMessage(kWhatMonitorQueue, id());
     msg->setInt32("generation", mMonitorQueueGeneration);
     msg->post(delayUs);
@@ -415,6 +432,7 @@ status_t PlaylistFetcher::onStart(const sp<AMessage> &msg) {
     if (mStartTimeUs >= 0ll) {
         mSeqNumber = -1;
         mStartup = true;
+        mPrepared = false;
     }
 
     postMonitorQueue();
@@ -456,40 +474,62 @@ void PlaylistFetcher::queueDiscontinuity(
 
 void PlaylistFetcher::onMonitorQueue() {
     bool downloadMore = false;
+    refreshPlaylist();
+
+    int32_t targetDurationSecs;
+    int64_t targetDurationUs = kMinBufferedDurationUs;
+    if (mPlaylist != NULL) {
+        CHECK(mPlaylist->meta()->findInt32("target-duration", &targetDurationSecs));
+        targetDurationUs = targetDurationSecs * 1000000ll;
+    }
 
-    status_t finalResult;
+    // buffer at least 3 times the target duration, or up to 10 seconds
+    int64_t durationToBufferUs = targetDurationUs * 3;
+    if (durationToBufferUs > kMinBufferedDurationUs)  {
+        durationToBufferUs = kMinBufferedDurationUs;
+    }
+
+    int64_t bufferedDurationUs = 0ll;
+    status_t finalResult = NOT_ENOUGH_DATA;
     if (mStreamTypeMask == LiveSession::STREAMTYPE_SUBTITLES) {
         sp<AnotherPacketSource> packetSource =
             mPacketSources.valueFor(LiveSession::STREAMTYPE_SUBTITLES);
 
-        int64_t bufferedDurationUs =
+        bufferedDurationUs =
                 packetSource->getBufferedDurationUs(&finalResult);
-
-        downloadMore = (bufferedDurationUs < kMinBufferedDurationUs);
         finalResult = OK;
     } else {
         bool first = true;
-        int64_t minBufferedDurationUs = 0ll;
 
         for (size_t i = 0; i < mPacketSources.size(); ++i) {
             if ((mStreamTypeMask & mPacketSources.keyAt(i)) == 0) {
                 continue;
             }
 
-            int64_t bufferedDurationUs =
+            int64_t bufferedStreamDurationUs =
                 mPacketSources.valueAt(i)->getBufferedDurationUs(&finalResult);
-
-            if (first || bufferedDurationUs < minBufferedDurationUs) {
-                minBufferedDurationUs = bufferedDurationUs;
+            if (first || bufferedStreamDurationUs < bufferedDurationUs) {
+                bufferedDurationUs = bufferedStreamDurationUs;
                 first = false;
             }
         }
+    }
+    downloadMore = (bufferedDurationUs < durationToBufferUs);
+
+    // signal start if buffered up at least the target size
+    if (!mPrepared && bufferedDurationUs > targetDurationUs && downloadMore) {
+        mPrepared = true;
 
-        downloadMore =
-            !first && (minBufferedDurationUs < kMinBufferedDurationUs);
+        ALOGV("prepared, buffered=%lld > %lld",
+                bufferedDurationUs, targetDurationUs);
+        sp<AMessage> msg = mNotify->dup();
+        msg->setInt32("what", kWhatTemporarilyDoneFetching);
+        msg->post();
     }
 
     if (finalResult == OK && downloadMore) {
+        ALOGV("monitoring, buffered=%lld < %lld",
+                bufferedDurationUs, durationToBufferUs);
         onDownloadNext();
     } else {
         // Nothing to do yet, try again in a second.
@@ -498,15 +538,17 @@ void PlaylistFetcher::onMonitorQueue() {
         msg->setInt32("what", kWhatTemporarilyDoneFetching);
         msg->post();
 
-        postMonitorQueue(1000000ll);
+        int64_t delayUs = mPrepared ? kMaxMonitorDelayUs : targetDurationUs / 2;
+        ALOGV("pausing for %lld, buffered=%lld > %lld",
+                delayUs, bufferedDurationUs, durationToBufferUs);
+        // :TRICKY: need to enforce minimum delay because the delay to
+        // refresh the playlist will become 0
+        postMonitorQueue(delayUs, mPrepared ? targetDurationUs * 2 : 0);
     }
 }
 
-void PlaylistFetcher::onDownloadNext() {
-    int64_t nowUs = ALooper::GetNowUs();
-
-    if (mLastPlaylistFetchTimeUs < 0ll
-            || (!mPlaylist->isComplete() && timeToRefreshPlaylist(nowUs))) {
+status_t PlaylistFetcher::refreshPlaylist() {
+    if (delayUsToRefreshPlaylist() <= 0) {
         bool unchanged;
         sp<M3UParser> playlist = mSession->fetchPlaylist(
                 mURI.c_str(), mPlaylistHash, &unchanged);
@@ -522,7 +564,7 @@ void PlaylistFetcher::onDownloadNext() {
             } else {
                 ALOGE("failed to load playlist at url '%s'", mURI.c_str());
                 notifyError(ERROR_IO);
-                return;
+                return ERROR_IO;
             }
         } else {
             mRefreshState = INITIAL_MINIMUM_RELOAD_DELAY;
@@ -535,6 +577,13 @@ void PlaylistFetcher::onDownloadNext() {
 
         mLastPlaylistFetchTimeUs = ALooper::GetNowUs();
     }
+    return OK;
+}
+
+void PlaylistFetcher::onDownloadNext() {
+    if (refreshPlaylist() != OK) {
+        return;
+    }
 
     int32_t firstSeqNumberInPlaylist;
     if (mPlaylist->meta() == NULL || !mPlaylist->meta()->findInt32(
@@ -553,12 +602,18 @@ void PlaylistFetcher::onDownloadNext() {
 
         if (mPlaylist->isComplete() || mPlaylist->isEvent()) {
             mSeqNumber = getSeqNumberForTime(mStartTimeUs);
+            ALOGV("Initial sequence number for time %lld is %ld from (%ld .. %ld)",
+                    mStartTimeUs, mSeqNumber, firstSeqNumberInPlaylist,
+                    lastSeqNumberInPlaylist);
         } else {
             // If this is a live session, start 3 segments from the end.
             mSeqNumber = lastSeqNumberInPlaylist - 3;
             if (mSeqNumber < firstSeqNumberInPlaylist) {
                 mSeqNumber = firstSeqNumberInPlaylist;
             }
+            ALOGV("Initial sequence number for live event %ld from (%ld .. %ld)",
+                    mSeqNumber, firstSeqNumberInPlaylist,
+                    lastSeqNumberInPlaylist);
         }
 
         mStartTimeUs = -1ll;
@@ -570,16 +625,34 @@ void PlaylistFetcher::onDownloadNext() {
             ++mNumRetries;
 
             if (mSeqNumber > lastSeqNumberInPlaylist) {
-                mLastPlaylistFetchTimeUs = -1;
-                postMonitorQueue(3000000ll);
+                // refresh in increasing fraction (1/2, 1/3, ...) of the
+                // playlist's target duration or 3 seconds, whichever is less
+                int32_t targetDurationSecs;
+                CHECK(mPlaylist->meta()->findInt32(
+                        "target-duration", &targetDurationSecs));
+                int64_t delayUs = mPlaylist->size() * targetDurationSecs *
+                        1000000ll / (1 + mNumRetries);
+                if (delayUs > kMaxMonitorDelayUs) {
+                    delayUs = kMaxMonitorDelayUs;
+                }
+                ALOGV("sequence number high: %ld from (%ld .. %ld), monitor in %lld (retry=%d)",
+                        mSeqNumber, firstSeqNumberInPlaylist,
+                        lastSeqNumberInPlaylist, delayUs, mNumRetries);
+                postMonitorQueue(delayUs);
                 return;
             }
 
             // we've missed the boat, let's start from the lowest sequence
             // number available and signal a discontinuity.
 
-            ALOGI("We've missed the boat, restarting playback.");
-            mSeqNumber = lastSeqNumberInPlaylist;
+            ALOGI("We've missed the boat, restarting playback."
+                  "  mStartup=%d, was  looking for %d in %d-%d",
+                    mStartup, mSeqNumber, firstSeqNumberInPlaylist,
+                    lastSeqNumberInPlaylist);
+            mSeqNumber = lastSeqNumberInPlaylist - 3;
+            if (mSeqNumber < firstSeqNumberInPlaylist) {
+                mSeqNumber = firstSeqNumberInPlaylist;
+            }
             explicitDiscontinuity = true;
 
             // fall through
diff --git a/media/libstagefright/httplive/PlaylistFetcher.h b/media/libstagefright/httplive/PlaylistFetcher.h
index 1648e02..78dea20 100644
--- a/media/libstagefright/httplive/PlaylistFetcher.h
+++ b/media/libstagefright/httplive/PlaylistFetcher.h
@@ -79,6 +79,7 @@ private:
     };
 
     static const int64_t kMinBufferedDurationUs;
+    static const int64_t kMaxMonitorDelayUs;
 
     sp<AMessage> mNotify;
     sp<LiveSession> mSession;
@@ -97,6 +98,7 @@ private:
     int32_t mSeqNumber;
     int32_t mNumRetries;
     bool mStartup;
+    bool mPrepared;
     int64_t mNextPTSTimeUs;
 
     int32_t mMonitorQueueGeneration;
@@ -120,10 +122,11 @@ private:
     status_t decryptBuffer(
             size_t playlistIndex, const sp<ABuffer> &buffer);
 
-    void postMonitorQueue(int64_t delayUs = 0);
+    void postMonitorQueue(int64_t delayUs = 0, int64_t minDelayUs = 0);
     void cancelMonitorQueue();
 
-    bool timeToRefreshPlaylist(int64_t nowUs) const;
+    int64_t delayUsToRefreshPlaylist() const;
+    status_t refreshPlaylist();
 
     // Returns the media time in us of the segment specified by seqNumber.
     // This is computed by summing the durations of all segments before it.