Centralize media element ownership in PlaybackObserver

[peaBerberian]

I was rebasing all my branches on dev and dived into one of my old PRs, #1754

This PR did two things:

1. Centralized ownership of the media element inside the PlaybackObserver (instead of handling it directly in the modules that needed it)
2. Renamed PlaybackObserver to MediaElementMonitor

For a review, (1) was much more interesting than (2).
Yet because the term PlaybackObserver is everywhere in the code, the rename was most of the diff and the interesting centralization part was lost in it.

I decided to split that PR in two. This one is only about (1), while #1754 continues to combine the logic and name change.

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Keeping the ownership of the media element in one single place simplified the implementation of multiple PoCs that have since been deprioritized: the preload feature (#1646) and the ""core dump"" feature.

Even without those two features, I still find the work interesting in that only one area would be changed when doing HTMLMediaElement-adjacent work instead of several.

Still not perfect though (re-reading it, formatMediaError could be moved into the PlaybackObserver, and there are remaining calls to getMediaElement that should be removed) - so there's still some work to do on it.

[github-actions]

✅ Automated performance checks have passed on commit 1fb923b8736fe2e7db4c5257fdf25a7aa6cc7761 with the base branch dev.

Details

Performance tests 1st run output

No significative change in performance for tests:

Name	Mean	Median
loading	24.69ms -> 26.41ms (-1.716ms, z: 2.68344)	34.50ms -> 34.65ms
seeking	221.04ms -> 200.58ms (20.457ms, z: 1.25667)	18.00ms -> 18.15ms
audio-track-reload	30.72ms -> 30.65ms (0.064ms, z: 1.06300)	44.90ms -> 44.70ms
cold loading multithread	51.36ms -> 50.68ms (0.677ms, z: 12.32689)	75.90ms -> 74.55ms
seeking multithread	209.06ms -> 187.85ms (21.214ms, z: 0.11138)	18.60ms -> 18.75ms
audio-track-reload multithread	29.93ms -> 29.93ms (-0.001ms, z: 1.11287)	43.95ms -> 43.80ms
hot loading multithread	20.55ms -> 20.47ms (0.084ms, z: 1.96686)	29.85ms -> 29.70ms

[github-actions]

✅ Automated performance checks have passed on commit 0873312ad6ad5608d899a702dc37e473aa9853f7 with the base branch dev.

Details

Performance tests 1st run output

No significative change in performance for tests:

Name	Mean	Median
loading	25.11ms -> 26.11ms (-1.002ms, z: 2.03351)	35.25ms -> 35.40ms
seeking	205.42ms -> 210.16ms (-4.738ms, z: 0.67067)	18.45ms -> 18.30ms
audio-track-reload	31.13ms -> 31.06ms (0.069ms, z: 0.63239)	45.60ms -> 45.45ms
cold loading multithread	52.08ms -> 52.55ms (-0.477ms, z: 11.68438)	77.10ms -> 75.45ms
seeking multithread	205.34ms -> 190.78ms (14.559ms, z: 0.89903)	19.05ms -> 19.35ms
audio-track-reload multithread	30.47ms -> 30.28ms (0.194ms, z: 0.58210)	44.45ms -> 44.40ms
hot loading multithread	21.08ms -> 20.90ms (0.181ms, z: 2.47230)	30.75ms -> 30.45ms

[github-actions]

✅ Automated performance checks have passed on commit 92be34f9ed1715caefd88778c5f9e074a84ed7ca with the base branch dev.

Details

Performance tests 1st run output

No significative change in performance for tests:

Name	Mean	Median
loading	25.35ms -> 25.72ms (-0.371ms, z: 2.44751)	35.70ms -> 35.85ms
seeking	187.89ms -> 191.92ms (-4.027ms, z: 0.67857)	18.75ms -> 18.60ms
audio-track-reload	32.33ms -> 32.28ms (0.056ms, z: 0.26793)	47.70ms -> 48.00ms
cold loading multithread	53.60ms -> 52.44ms (1.154ms, z: 16.13092)	78.90ms -> 77.25ms
seeking multithread	91.44ms -> 88.32ms (3.123ms, z: 2.69874)	20.55ms -> 21.00ms
audio-track-reload multithread	31.29ms -> 31.36ms (-0.065ms, z: 0.23517)	45.90ms -> 45.90ms
hot loading multithread	21.21ms -> 21.93ms (-0.711ms, z: 0.99020)	31.05ms -> 30.90ms

[github-actions]

✅ Automated performance checks have passed on commit 2d9f02fd20e8f4d8b9c9535d179992896bf74141 with the base branch dev.

Details

Performance tests 1st run output

No significative change in performance for tests:

Name	Mean	Median
loading	36.81ms -> 37.09ms (corrected: 1.947ms, A/A bias: -2.228ms, z: 0.23094)	30.40ms -> 30.30ms (corrected: -0.325ms, A/A bias: 0.000ms, z: 0.84678)
seeking	141.51ms -> 176.59ms (corrected: -85.165ms, A/A bias: 50.088ms, z: 2.43449)	11.50ms -> 11.75ms (corrected: -0.300ms, A/A bias: 0.325ms, z: 1.42894)
audio-track-reload	31.72ms -> 31.59ms (corrected: 0.210ms, A/A bias: -0.076ms, z: 0.58697)	30.40ms -> 30.40ms (corrected: 0.475ms, A/A bias: -0.400ms, z: 1.28942)
loading over active content	23.12ms -> 24.02ms (corrected: -0.949ms, A/A bias: 0.045ms, z: 0.97187)	21.10ms -> 21.85ms (corrected: -2.200ms, A/A bias: 0.050ms, z: 0.97187)
large multi-period manifest	93.76ms -> 94.90ms (corrected: -1.909ms, A/A bias: 0.761ms, z: 0.86603)	84.90ms -> 87.50ms (corrected: -4.375ms, A/A bias: 3.225ms, z: 0.86603)
cold loading multithread	53.73ms -> 52.01ms (corrected: 1.748ms, A/A bias: -0.034ms, z: 2.77128)	51.75ms -> 50.50ms (corrected: 1.175ms, A/A bias: -0.125ms, z: 4.48409)
seeking multithread	193.67ms -> 216.29ms (corrected: 29.733ms, A/A bias: -52.352ms, z: 0.73131)	13.80ms -> 14.10ms (corrected: -0.100ms, A/A bias: -0.100ms, z: 0.12990)
audio-track-reload multithread	30.86ms -> 30.80ms (corrected: 0.003ms, A/A bias: 0.055ms, z: 0.17321)	29.90ms -> 29.85ms (corrected: 0.325ms, A/A bias: -0.075ms, z: 0.76980)
hot loading multithread	21.45ms -> 21.13ms (corrected: 0.168ms, A/A bias: 0.151ms, z: 0.55811)	20.50ms -> 20.30ms (corrected: 0.000ms, A/A bias: 0.000ms, z: 0.47150)