Unhandled ArrayIndexOutOfBoundsException during live HLS playback when media sequence unexpectedly changes to zero

[gpinigin]

Description

Unhandled ArrayIndexOutOfBoundsException during live HLS playback when media sequence unexpectedly changes to zero. First segment in new index file has no EXT-X-DISCONTINUITY tag added (according to HLS spec absence of tag may lead to playback error)

Reports gathered with Fabric show that negative index is close to value of last known media sequence.

Version

ExoPlayer v2.1.1

Stack trace

Fatal Exception: java.lang.ArrayIndexOutOfBoundsException: length=12; index=-4310639
       at java.util.ArrayList.get(ArrayList.java:310)
       at java.util.Collections$UnmodifiableList.get(Collections.java:1050)
       at com.google.android.exoplayer2.source.hls.playlist.HlsPlaylistTracker.adjustPlaylistTimestamps(HlsPlaylistTracker.java:371)
       at com.google.android.exoplayer2.source.hls.playlist.HlsPlaylistTracker.access$1300(HlsPlaylistTracker.java:40)
       at com.google.android.exoplayer2.source.hls.playlist.HlsPlaylistTracker$MediaPlaylistBundle.processLoadedPlaylist(HlsPlaylistTracker.java:465)
       at com.google.android.exoplayer2.source.hls.playlist.HlsPlaylistTracker$MediaPlaylistBundle.onLoadCompleted(HlsPlaylistTracker.java:422)
       at com.google.android.exoplayer2.source.hls.playlist.HlsPlaylistTracker$MediaPlaylistBundle.onLoadCompleted(HlsPlaylistTracker.java:381)
       at com.google.android.exoplayer2.upstream.Loader$LoadTask.handleMessage(Loader.java:355)
       at android.os.Handler.dispatchMessage(Handler.java:111)
       at android.os.Looper.loop(Looper.java:194)
       at android.os.HandlerThread.run(HandlerThread.java:61)
       at com.google.android.exoplayer2.util.PriorityHandlerThread.run(PriorityHandlerThread.java:40)

[ojw28]

I think you're confusing two separate topics. Use of the EXT-X-DISCONTINUITY tag allows various properties of the media segments to change (e.g. the encoding parameters). It does not make it OK to reset the media sequence number to zero, which is something that should never happen. The spec says this about the media sequence number:

Its value MUST be incremented by 1 for every Media Segment that is removed from the Playlist file; it MUST NOT decrease or wrap. Clients can malfunction if each Media Segment does not have a consistent, unique Media Sequence Number.

Marking this as a bug, but only because the exception isn't handled and causes process death, which isn't desirable. We'll fix this to cause a playback failure instead.

[gpinigin]

You are right, thank you for pointing out to this aspect.

Marking this as a bug, but only because the exception isn't handled and causes process death, which isn't desirable. We'll fix this to cause a playback failure instead.

It was the main intention.

[ojw28]

For the stack trace to occur as in this issue report, it looks like a required condition is:

newPlaylist.mediaSequence < oldPlaylist.mediaSequence

And also that:

newPlaylist.isNewerThan(oldPlaylist)

Else the method would have returned at this line.

Are you still able to reproduce the issue? If so, can you take a look and see why isNewerThan is evaluating to true in this case? The only way I can see this happening is if the new playlist not only has media sequence set back to 0, but if it also has an end tag appended when the old one didn't. Is that what's happening? If not, what is? Thanks.

[gpinigin]

If so, can you take a look and see why isNewerThan is evaluating to true in this case? The only way I can see this happening is if the new playlist not only has media sequence set back to 0, but if it also has an end tag appended when the old one didn't.

End tag is appended to the new playlist also. I think appending end tag is the only reason why isNewerThan returns true

Just for clarification – due streaming service malfunction in some rare cases client is being redirected from live HLS stream to static HLS VOD. VOD playlist doesn't contain any segments from the preceding playlist.

[ojw28]

Our plan for handling this case is to create a new playlist consisting of the old playlist with the end tag appended (i.e. just treat the playback as though it's ended).