Handle missing audio in some periods of a multi-period stream

[mariocynicys]

Have you read the FAQ and checked for duplicate open issues?
Yes

What version of Shaka Player are you using?
v3.0.10-master-18-g1b1227f4-debug

Are you using the demo app or your own custom app?
Custom

What browser and OS are you using?
Chrome on Ubuntu 18.04

What did you do?
Concatenated two single-period dash manifests into one 2-period manifest.
one of them was audio-less, just video.
the other one was video+audio.

What did you expect to happen?
To have audio in the first period but no audio in the second.

What actually happened?
No audio in both periods.

further info
When both periods have audio, audio plays fine in both of them.

[joeyparrish]

We can't add or remove SourceBuffers (switch from audio+video to video-only or vice-versa) during playback because we set up one continuous pipeline for playback across all periods. In the current design of Shaka Player, this is a scenario we can't support.

This also seems fairly unrealistic for streaming media sites, so I'm not inclined to have the team spend time or energy on this scenario in the player. However, it could be prevented with relatively ease in Shaka Streamer.

@meryacine, can you consider one of these options for after your core work on multi-period in Streamer is complete?

If one period has audio and another does not, either:

1. pad audio-less periods with silence in ffmpeg during transcoding
2. warn or throw an error to reject this input scenario

I would suggest you not do either until the other work is complete, but I think these could both be helpful solutions on the encoding/packaging side.

[joeyparrish]

I'm going to migrate this issue to the Streamer repo now and rename it as an enhancement to Streamer to handle this scenario differently.

[joeyparrish]

Depends on #43