Adds support for fragmented mp4 with multiple sidx boxes

[anthonybajoua]

Summary:

Addresses Github issue #9373
Implements solution 1 proposed by Google maintainer.

• Added test. Generated test file using below command:

ffmpeg -i short_1080p_videoonly_lowbitrate.mp4 -c copy -movflags frag_keyframe+delay_moov+empty_moov+dash sample_fragmented_seekable_multi_sidx.mp4 (Above movflags flags actually result in an unplayable file on this player until this fix.)

Algorithm/Solution

1. Upon encountering multiple sidx atom in track:
2. For each atom in the track:
   1. If sidx atom then aggregate ChunkIndex into master list, else skip
   2. Merge them all into one large chunk index.
   3. Reset the seek pointer to where it was last
      Retry above on I/O failures.

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[colinkho]

Hey @tonihei @icbaker , would you guys be able to take a look? This would help us maintain a vanilla fMp4 extractor!

[icbaker]

We can take a look once the CLA check is passing.

[oceanjules]

@anthonybajoua Hey, a reminder to complete the CLA instruction if you want us to look at your code :)

[colinkho]

Seems like the CLA issue is finally resolved. @icbaker Would you be able to take a look?

[Shell1125]

Details

[rohitjoins]

We're still investigating the use of finally block here. Extractor should be able to restart from an IOException without having this. Removing this block results in test failures with IO Errors simulation.

[anthonybajoua]

This is due to the reset of the seek position being set and not cleared during an IO Error.

https://gist.github.com/anthonybajoua/c85a786a30f9876c82849544f848f190

See the above revision for a much cleaner way to achieve this.