Analytics onLoad events for HttpMediaDrmCallback requests

[stevemayhew]

Use case description

An often significant delay for first frame with channel tunes occurs because of delays from the DRM License Server key or provisioning requests, it would be nice to have analytics events for these.

Proposed solution

The standard MediaSourceEventListener report details for DATA_TYPE_DRM for fetches from EXT-X-KEY with an actual key URL, However the same level of details is missing from the DrmSessionEventListener events.

We could:

1. Add load statistics to the existing drmKeysLoaded event
2. Add two new events (drmKeyRequestStarted, drmKeyRequestCompleted)

Alternatives considered

Adding logging to the HttpMediaDrmCallback, this is simple but not as useful as a hook that allowed using AnalyticsListener to post the data to operational logging.

[stevemayhew]

@icbaker I'm curious why DefaultDrmSession.RequestHandler was even implemented rather than using the existing com.google.android.exoplayer2.upstream.Loader. which does largely the same thing with a richer set of API calls to observe and manage the load.

[icbaker]

Alternatives considered

Adding logging to the HttpMediaDrmCallback, this is simple but not as useful as a hook that allowed using AnalyticsListener to post the data to operational logging.

Not sure if this is what you meant, but to be explicit: you can add a TransferListener to the DataSource.Factory you pass to HttpMediaDrmCallback, and you should get some callbacks including URLs etc.

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@icbaker I'm curious why DefaultDrmSession.RequestHandler was even implemented rather than using the existing com.google.android.exoplayer2.upstream.Loader.

Good question - I'm afraid I don't know the reasoning at the time, but I suspect it might have been felt that the Loader machinery was a bit heavyweight for "just" making an HTTP request that you expect to complete fairly quickly (vs e.g. keeping a long-running HTTP request open while you load a whole MP4 movie).

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We could:

1. Add load statistics to the existing drmKeysLoaded event
2. Add two new events (drmKeyRequestStarted, drmKeyRequestCompleted)

I like (1) more than (2), because we could also include additional info like the type of key load (offline, renewal, etc).

Is this something you'd like to send a PR for? I suggest keeping the existing DrmSessionEventListener.onDrmKeysLoaded(int windowIndex, MediaSource.MediaPeriodId) method and deprecating it, then adding a new onDrmKeysLoaded(int, MediaPeriodId, KeyLoadInfo) method (type name TBD). You will want to ensure that both are invoked from DrmSessionEventListener.EventDispatcher.drmKeysLoaded. Similar on AnalyticsListener (though without the duplication there - each method should just forward directly I think, to avoid too much duplication).

You can probably hard-update the DrmSessionEventListener.EventDispatcher.drmKeysLoaded method to take the new KeyLoadInfo type without deprecating the zero-arg overload, since direct usages of that are probably quite rare (custom DrmSessionManager impls only really) - and maintaining both becomes tricky (since you have to synthesise a 'fake' KeyLoadInfo which is a bit confusing).

[stevemayhew]

You can probably hard-update the DrmSessionEventListener.EventDispatcher.drmKeysLoaded method to take the new KeyLoadInfo type without deprecating the zero-arg overload, since direct usages of that are probably quite rare (custom DrmSessionManager impls only really) - and maintaining both becomes tricky (since you have to synthesise a 'fake' KeyLoadInfo which is a bit confusing).

Thanks, yes the method DrmSessionEventListener.EventDispatcherdrmKeysLoadedO is public, but not really an API so adding the KeyLoadInfo object should not be a problem. We'll work on the pull request.

[stevemayhew]

@icbaker Here's the pull request with first pass: https://github.com/androidx/media/pull/1134

I need to plumb through to AnalyticsListener in order for it to be useful, wanted to stop before I got to far and get your feedback.

You should have access to my repo if you want to suggest changes in code feel free to branch and make pull requests, add commits, or just comment on the pull

THanks!