improve track switch process

[nicosang]

Hi,

this PR has to improve fast track switch process and not reload abandonned request in this use case. As mentionned by @nweber, there was an issue when fast video track switch occured.

@nweber , could you, please, give us a feedback?

Nico

[nweber]

@nicosang Sorry for the delay, but I finally got time to test this today.

The latest development build still stutters fairly consistently for video when using "always replace".

Manifest:
https://s3.amazonaws.com/ssi-us-east-1-elemental-hls/bbb/streams/bbb.mpd

Reference Player:
http://reference.dashif.org/dash.js/nightly/samples/dash-if-reference-player/index.html?url=https://s3.amazonaws.com/ssi-us-east-1-elemental-hls/bbb/streams/bbb.mpd

Steps to reproduce:

1. Open nightly reference player link above.
2. Expand options and change the "Track Switch Mode" for Video to "Always Replace".
3. Load the video.
4. Use the three bars icon in the control bar to toggle to the unselected video track.

When switching, the video does keep playing during the switch but then I consistently see the video stall for ~1-3 seconds when the new track data is rendered. I'm not sure why the stall is happening, but playback shouldn't stall when switching.

[nweber]

@nicosang Compare the above to version 2.5.0:

http://reference.dashif.org/dash.js/v2.5.0/samples/dash-if-reference-player/index.html?url=https://s3.amazonaws.com/ssi-us-east-1-elemental-hls/bbb/streams/bbb.mpd

The track switch for video is seamless in this version.

[nicosang]

Hi @nweber ,

first of all, indeed, there is still weird behavior with the video track switch. I have to look at it more precisely.

Nevertheless, it seems that your manifest should have different representation id in the different AdaptationSet of the unique period as described in the DASH spec (ISO/IEC 23009-1:2014) in section 5.3.5.2.

If you do agree, could you, please, update it?

Thanks,

Nico

[nweber]

@nicosang

Section 5.3.5.2 says..

id specifies an identifier for this Representation. The identifier shall be unique within a Period unless the Representation is functionally identically to another Representation in the same Period.

I believe that in this case that the Representation nodes that have the same id values are "functionality equivalent", as they are in different AdaptationSets. They represent the same content and are encoded the same way (timing, codec, etc); in other words, the same init will work for both sets of content.