Packager doesn't handle subtitle tracks inside MP4 files (IMSC1)

[duggaraju]

System info

Operating System: all
Shaka Packager Version: v2.6.1-634af65-release

Issue and steps to reproduce the problem

Packager Command:
packager-win-x64.exe "in=sample.mp4" --dump_stream_info
[0607/173210:INFO:demuxer.cc(89)] Demuxer::Run() on file 'English.cmft'.
[0607/173211:INFO:demuxer.cc(155)] Initialize Demuxer for file 'English.cmft'.

File "sample.mp4":
Found 0 stream(s).
Extra steps to reproduce the problem?
(1)
(2)

What is the expected result?
The subtitle track is recognized.

What happens instead?

in bool MP4MediaParser::ParseMoov(BoxReader* reader) in mp4_media_parser.cc
We only handle kAudio/kVideo track types.
kSubtitle tracks are ignored.
<Please attach the input files or email to shaka-packager-issues@google.com.>

[duggaraju]

sample.mp4