Fatal IndexOutOfBoundsException thrown when Media3 PreloadManager is enabled

[jasongrife]

Version

Media3 1.8.0

More version details

No response

Devices that reproduce the issue

Any Android device

Devices that do not reproduce the issue

No response

Reproducible in the demo app?

Not tested

Reproduction steps

With an .m3u8 manifest file such as this one:

#EXTM3U
#EXT-X-PROGRAM-DATE-TIME:2019-01-01T00:00:00.000Z
#EXT-X-TARGETDURATION:6
#EXT-X-ALLOW-CACHE:YES
#EXT-X-PLAYLIST-TYPE:VOD
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:1
#EXT-X-ENDLIST

Which has missing Segments.

Then in Media3 Exoplayer when you seekToPlaylistItem without preloading enabled, you get an IndexOutOfBoundsException that gets caught and instead of crashing the app, is pushed out to the Player.Listener#onPlayerError

However, with PreloadManager enabled the Media3 Exoplayer code will not catch the IndexOutOfBoundsException and instead the app crashes.

Expected result

The expectation would be that for Preloading enabled, this exception would be caught as well. And then either thrown to Player.Listener#onPlayerError or PreloadManagerListener#onError, or both.

Actual result

Logs for Media3 Exoplayer attemplting to play that .m3u8 with the missing Segments. Showing it gets caught as a Playback error and not a crashing exception:

Playback error
androidx.media3.exoplayer.ExoPlaybackException: Unexpected runtime error
    at androidx.media3.exoplayer.ExoPlayerImplInternal.handleMessage(ExoPlayerImplInternal.java:911)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loopOnce(Looper.java:248)
    at android.os.Looper.loop(Looper.java:338)
    at android.os.HandlerThread.run(HandlerThread.java:85)
Caused by: java.lang.IndexOutOfBoundsException: index (0) must be less than size (0)
    at com.google.common.base.Preconditions.checkElementIndex(Preconditions.java:1372)
    at com.google.common.base.Preconditions.checkElementIndex(Preconditions.java:1354)
    at com.google.common.collect.RegularImmutableList.get(RegularImmutableList.java:84)
    at androidx.media3.exoplayer.hls.HlsChunkSource.getNextMediaSequenceAndPartIndex(HlsChunkSource.java:910)
    at androidx.media3.exoplayer.hls.HlsChunkSource.createMediaChunkIterators(HlsChunkSource.java:769)
    at androidx.media3.exoplayer.hls.HlsChunkSource.getNextChunk(HlsChunkSource.java:451)
    at androidx.media3.exoplayer.hls.HlsSampleStreamWrapper.continueLoading(HlsSampleStreamWrapper.java:802)
    at androidx.media3.exoplayer.source.CompositeSequenceableLoader$SequenceableLoaderWithTrackTypes.continueLoading(CompositeSequenceableLoader.java:178)
    at androidx.media3.exoplayer.source.CompositeSequenceableLoader.continueLoading(CompositeSequenceableLoader.java:131)
    at androidx.media3.exoplayer.hls.HlsMediaPeriod.continueLoading(HlsMediaPeriod.java:408)
    at androidx.media3.exoplayer.source.MaskingMediaPeriod.continueLoading(MaskingMediaPeriod.java:229)
    at androidx.media3.exoplayer.MediaPeriodHolder.continueLoading(MediaPeriodHolder.java:253)
    at androidx.media3.exoplayer.ExoPlayerImplInternal.maybeContinueLoading(ExoPlayerImplInternal.java:3060)
    at androidx.media3.exoplayer.ExoPlayerImplInternal.handleContinueLoadingRequested(ExoPlayerImplInternal.java:3021)
    at androidx.media3.exoplayer.ExoPlayerImplInternal.handleMessage(ExoPlayerImplInternal.java:740)

Crashing IndexOutOfBoundsException stacktrace, when Preloading is enabled:

E  FATAL EXCEPTION: ExoPlayer:Playback
Process: -----
java.lang.IndexOutOfBoundsException: index (0) must be less than size (0)
    at com.google.common.base.Preconditions.checkElementIndex(Preconditions.java:1372)
    at com.google.common.base.Preconditions.checkElementIndex(Preconditions.java:1354)
    at com.google.common.collect.RegularImmutableList.get(RegularImmutableList.java:84)
    at androidx.media3.exoplayer.hls.HlsChunkSource.getNextMediaSequenceAndPartIndex(HlsChunkSource.java:910)
    at androidx.media3.exoplayer.hls.HlsChunkSource.createMediaChunkIterators(HlsChunkSource.java:769)
    at androidx.media3.exoplayer.hls.HlsChunkSource.getNextChunk(HlsChunkSource.java:451)
    at androidx.media3.exoplayer.hls.HlsSampleStreamWrapper.continueLoading(HlsSampleStreamWrapper.java:802)
    at androidx.media3.exoplayer.source.CompositeSequenceableLoader$SequenceableLoaderWithTrackTypes.continueLoading(CompositeSequenceableLoader.java:178)
    at androidx.media3.exoplayer.source.CompositeSequenceableLoader.continueLoading(CompositeSequenceableLoader.java:131)
    at androidx.media3.exoplayer.hls.HlsMediaPeriod.continueLoading(HlsMediaPeriod.java:408)
    at androidx.media3.exoplayer.source.preload.PreloadMediaPeriod.continueLoading(PreloadMediaPeriod.java:274)
    at androidx.media3.exoplayer.source.preload.PreloadMediaSource$PreloadMediaPeriodCallback.lambda$onContinueLoadingRequested$1$androidx-media3-exoplayer-source-preload-PreloadMediaSource$PreloadMediaPeriodCallback(PreloadMediaSource.java:523)
    at androidx.media3.exoplayer.source.preload.PreloadMediaSource$PreloadMediaPeriodCallback$$ExternalSyntheticLambda1.run(D8$$SyntheticClass:0)
    at android.os.Handler.handleCallback(Handler.java:995)
    at android.os.Handler.dispatchMessage(Handler.java:103)
    at android.os.Looper.loopOnce(Looper.java:248)
    at android.os.Looper.loop(Looper.java:338)
    at android.os.HandlerThread.run(HandlerThread.java:85)

Media

index-svtt.m3u8

Response body:
#EXTM3U
#EXT-X-PROGRAM-DATE-TIME:2019-01-01T00:00:00.000Z
#EXT-X-TARGETDURATION:6
#EXT-X-ALLOW-CACHE:YES
#EXT-X-PLAYLIST-TYPE:VOD
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:1
#EXT-X-ENDLIST

Bug Report

• You will email the zip file produced by adb bugreport to android-media-github@google.com after filing this issue.

[tianyif]

Hi @jasongrife,

Thanks for reporting this issue! I just reproduced on 1.8.0, it looks like for playback without preload manager, we only have this error logged at LoaderTask level, but don't surface it as ExoPlaybackException, thus the playback screen remain dark without reporting error. Is 1.8.0 the version that you saw the ExoPlaybackException?

Anyway we should fix both ExoPlayer and DefaultPreloadManager.

[jasongrife]

Is 1.8.0 the version that you saw the ExoPlaybackException?

@tianyif Yes. We are running 1.8.0 and that is the version we saw the exception and crash being thrown.

[tianyif]

Hi @jasongrife,

I just pushed a commit yesterday for fixing this issue. I still couldn't reproduce ExoPlaybackException from the player. Instead, what I saw was the playback screen remained dark but error was logged at LoaderTask level. However I could reproduce the crash from the preload manager.

The reason behind the different behaviours is - when the empty HlsMediaPlaylist completed loading, the below callback.onLoadCompleted is called,

media/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/upstream/Loader.java

Lines 518 to 524 in bfe5930

	try {
	callback.onLoadCompleted(loadable, nowMs, durationMs);
	} catch (RuntimeException e) {
	// This should never happen, but handle it anyway.
	Log.e(TAG, "Unexpected exception handling load completed", e);
	fatalError = new UnexpectedLoaderException(e);
	}

As the result of this callback, either player or the PreloadMediaSource from preload manager will attempt to continue loading a chunk to prepare the period, where IndexOutOfBoundsException got triggered. The player synchronously calls continueLoading for the period, but the PreloadMediaSource asynchronously queues an event which calls continueLoading, thus the former case could be immediately caught by the above try-catch structure, but the latter couldn't.

For the former case, once this is caught as a fatal error, it didn't get surfaced as ExoPlaybackException (at least from my side), because the MaskingMediaPeriod just tries to throw the mediaPeriod error if it is present, but a fatal error belongs to DefaultHlsPlaylistTracker's loader (which is supposed to throw from MediaSource) didn't finally throw. See below -

media/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/MaskingMediaPeriod.java

Lines 154 to 160 in bfe5930

	public void maybeThrowPrepareError() throws IOException {
	try {
	if (mediaPeriod != null) {
	mediaPeriod.maybeThrowPrepareError();
	} else if (mediaSource != null) {
	mediaSource.maybeThrowSourceInfoRefreshError();
	}

Back to this problem specifically. I didn't immediately do assertion that a media playlist without any Segment is malformed. I just made it to the logic where we can mark the empty segment in a VOD playlist as end of stream. For Live playlist, it can either load a trailing part or refresh the playlist. And specifically for the VOD case, if your just provide such an empty media playlist without multivariant playlist, you will still get a ParseException (should be surfaced as ExoPlaybackException) with message Loading finished before preparation is complete, which makes sense, as without multivariant playlist, an HLS stream has to load a chunk to complete the preparation (get timeline, tracks such information), but there is no way to do that. And if you provide a valid multivariant playlist and then such an empty media playlist, there is unlikely a ParseException. As chunkless preparation can be done with multivariant playlist, and an empty media playlist just means a stream with no content at all.