feat: CMCD v2 LTC and MSD keys

[JoaquinBCh]

This PR introduces two new CMCD v2 keys to shaka player:

• ltc (live stream latency): The time delta between when a given media timestamp was made available at the origin and when it was rendered by the client.
• msd (media start delay): Measures the initial delay in wall-clock time from when a player is instructed to play media for a given session to when any media begins playback. (This is sent only once when it is calculated)

While this update does not implement full CMCD v2 support, it extends the CMCD v1 implementation to handle these two new values when requested.

Summary:

• Updated the player settings: cmcd.reporting.requestMode.version must be set to 2 to use these new CMCD v2 keys.
• Implemented logic to retrieve the values for ltc and msd if requested and if the version is set to 2.
• Implemented logic to send the msd value only once.
• Created getLiveLatency() method in player to calculate the latency and use it for ltc.
• Created unit tests for the two new keys (ltc and msd) to ensure their correct behavior when cmcd.reporting.requestMode.version is set to 2.

Testing:

• Verified that the ltc and msd keys are included when the reporting version is set to 2 and these keys are requested. And the msd key is sent only once when it is calculated.
• Verified that these keys are not included when the version is set to 1 or it is not set.

How to Test manually:

Test that msd and ltc values are sent correctly

Set the following configuration to the player:

player.configure({
  cmcd: {
    enabled: true,
    version: 2,
    includeKeys: ['sid', 'cid', 'v', 'msd', 'ltc'],
  }
});

Verify that the msd value is sent only once after being calculated, and the ltc value is sent with every request.

Test the msd value is calculated correctly

Use throttling in your browser to slow down your connection and reproduce the streaming.

The msd value should be higher than usual.

Notes:

• This PR adds support for the ltc and msd keys but does not implement the entire CMCD v2

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[shaka-bot]

Incremental code coverage: 95.77%

[tykus160]

Thanks for your contribution! Here are a few suggestions.
Additionally, it looks like you didn't sign CLA. Please check it.

[avelad]

Please sign the CLA!

[joeyparrish]

I would also like @littlespex to review this. This week, he and I discussed his plans for CMCD v2, so I want to make sure this does not complicate those plans.

[littlespex]

My initial thoughts:

1. The new CMCD keys and serialization rules will all be replaced by the CML enums and utilities. Until that happens I don't see anything wrong with defining them along with the other internal CMCD type defs.
2. New internal functions for tracking state like getLiveLatency will be useful even after CML is introduced.
3. Changes to the player config need thorough review as they are the only public API facing code, and we won't be able to change that later without introducing a breaking change/version. V2 adds some complexity with the different delivery modes, and calls into question some how some of the current properties like includeKeys will work with these new modes. The config changes in this PR are based on similar work in dash.js. I am reviewing this proposed structure to see if it will also work for shaka.

[JoaquinBCh]

Thanks everyone for the reviews.
@avelad we've already signed the CLA, but we haven't been added as members of the organization yet. We're expecting to have this resolved as soon as possible

[littlespex]

I would like to get an answer to this question before approving/rejecting this PR:

cta-wave/common-media-client-data#138 (comment)
cta-wave/common-media-client-data#146

[JoaquinBCh]

Hi @littlespex,
I was following the discussion about the structure you suggested to use, and based on my understanding for this PR where we only implemented ltc and msd we should place the version field outside of reporting and requestMode, and add ltc and msd to the enabledKeys list.
An example configuration could be:

cmcd: {
    enabled: true,
    version: 2,
    enabledKeys: ['sid', 'cid', 'v', 'msd', 'ltc'],
},

If this looks good to you, I can proceed with the changes.

[littlespex]

The only things that needs to change is adding the version property to the top level cmcd config. enabledKeys is a dash.js key, in shaka it's includeKeys. That said, you shouldn't need to do anything there. If the player is configured for v2, then those keys will be included by default.

[avelad]

Overall LGTM just a few more minor changes.

[avelad]

LGTM, I leave final approval and merge to @littlespex

Reviewed by Wojciech and Alvaro