ParserException for DASH Subtitles (WebVTT in MP4 container)

[bhjortsberg]

[REQUIRED] Issue description

This stream worked fine in 2.11.8
https://storage.googleapis.com/shaka-demo-assets/angel-one/dash.mpd

On ExoPlayer 2.12.0 I get this:

2020-09-24 22:22:52.987 6762-7202/com.mtdeer.exostreamr E/TextRenderer: Subtitle decoding failed. streamFormat=Format(2, null, application/mp4, text/vtt, wvtt, 736, en, [-1, -1, -1.0], [-1, -1])
      com.google.android.exoplayer2.text.SubtitleDecoderException: com.google.android.exoplayer2.ParserException: Expected WEBVTT. Got �����vtte
        at com.google.android.exoplayer2.text.webvtt.WebvttDecoder.decode(WebvttDecoder.java:63)
        at com.google.android.exoplayer2.text.SimpleSubtitleDecoder.decode(SimpleSubtitleDecoder.java:73)
        at com.google.android.exoplayer2.text.SimpleSubtitleDecoder.decode(SimpleSubtitleDecoder.java:27)
        at com.google.android.exoplayer2.decoder.SimpleDecoder.decode(SimpleDecoder.java:234)
        at com.google.android.exoplayer2.decoder.SimpleDecoder.run(SimpleDecoder.java:198)
        at com.google.android.exoplayer2.decoder.SimpleDecoder.access$000(SimpleDecoder.java:29)
        at com.google.android.exoplayer2.decoder.SimpleDecoder$1.run(SimpleDecoder.java:72)
     Caused by: com.google.android.exoplayer2.ParserException: Expected WEBVTT. Got �����vtte
        at com.google.android.exoplayer2.text.webvtt.WebvttParserUtil.validateWebvttHeaderLine(WebvttParserUtil.java:45)
        at com.google.android.exoplayer2.text.webvtt.WebvttDecoder.decode(WebvttDecoder.java:61)
        at com.google.android.exoplayer2.text.SimpleSubtitleDecoder.decode(SimpleSubtitleDecoder.java:73) 
        at com.google.android.exoplayer2.text.SimpleSubtitleDecoder.decode(SimpleSubtitleDecoder.java:27) 
        at com.google.android.exoplayer2.decoder.SimpleDecoder.decode(SimpleDecoder.java:234) 
        at com.google.android.exoplayer2.decoder.SimpleDecoder.run(SimpleDecoder.java:198) 
        at com.google.android.exoplayer2.decoder.SimpleDecoder.access$000(SimpleDecoder.java:29) 
        at com.google.android.exoplayer2.decoder.SimpleDecoder$1.run(SimpleDecoder.java:72) 

[REQUIRED] Reproduction steps

Stream https://storage.googleapis.com/shaka-demo-assets/angel-one/dash.mpd
and select any of the subtitle tracks.

[REQUIRED] Link to test content

https://storage.googleapis.com/shaka-demo-assets/angel-one/dash.mpd

[REQUIRED] A full bug report captured from the device

bugreport-sdk_gphone_x86-QSR1.191030.002-2020-09-24-22-36-21.zip

[REQUIRED] Version of ExoPlayer being used

2.12.0

[REQUIRED] Device(s) and version(s) of Android being used

Android 10 on Pixel 3a emulator

[marcbaechinger]

The dash stream defines text tracks in application/mp4 and the stack trace suggests that the WebvttParserUtil reads a binary file while expecting a text file. ExoPlayer supports separate text tracks for text mime types as documented in the developer guide.

[marcbaechinger]

Seems like I'm wrong and this worked before 2.12. Thanks @icbaker for letting me know. :)