Require at least one block from each audio and video track in media segment definition

[wolenetz]

Migrated from w3c bugzilla tracker. For history prior to migration, please see:
https://www.w3.org/Bugs/Public/show_bug.cgi?id=29188

Per the MSE teleconf today, @jdsmith3000 was in the process of getting the answer to https://www.w3.org/Bugs/Public/show_bug.cgi?id=29188#c1.

Jerry, please update this bug once you have more information.

[jdsmith3000]

We don't know of any implementers that would be affected by this change.

We would favor language that recommended roughly equal durations of audio and video in each segment, rather than saying there should be at least one block of each, which leaves open failure cases that would be encountered if blocks are not equal (to the degree possible) in length.

[wolenetz]

The "at least one block from each audio and video track" gives a clear line that, if crossed, leads to decode error in an interoperable fashion. We could also put a non-normative note that describes further the "roughly equal durations" language. Does this sound ok? If so, please assign back to me and change to "needs implementation".

[wolenetz]

I'm beginning work on a PR for this today.

[wolenetz]

PR is pending review at #43

[wolenetz]

From the discussion on the PR (#43), requiring one block from each audio and video track in a muxed stream is too strict. If we need some alternative clarification of a more lenient requirement, please open a distinct issue.