Allows exact live sync for HLS #703
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This commit addresses the issue of inaccurate live position measurement in HLS by introducing NTP time synchronization. Unlike DASH, HLS lacks origin time synchronization logic, resulting in potential discrepancies in wall-clock time when using `System.currentTimeMillis()`. The commit utilizes the `SntpClient` in ExoPlayer to determine the clock offset with the default NTP server (`time.android.com`) and applies this information to the `HlsMediaSource`. With the implementation of this change, multiple devices can now synchronize playback to a common time source, as long as the origin server also synchronizes to an NTP time source.
Enables testing the Live Offset settings with the main demo PlayerActivity. Using an intent like: ``` adb shell am start -n androidx.media3.demo.main/.PlayerActivity -a androidx.media3.demo.main.action.VIEW --ei live_offset_target 30 --ef live_offset_adjust_speed 35.0 ``` Will start playback synced to a 30 second offset with agressive speed adjustment to achive it, note this requires audio codec that supports speed changes (AAC for example)
| /* elapsedRealtimeEpochOffsetMs= */ C.TIME_UNSET, | ||
| SntpClient.getElapsedRealtimeOffsetMs(), | ||
| periodDurationUs, |
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If the SntpClient is not initialized this change done nothing, so you could consider making the changes to DefaultHlsPlaylistTracker surrounded by a feature flag from the HlsPlaylistTracker.Factory (if it was not private), or simply a PSFB flag.
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| private void requestMasterPlaylist( | ||
| EventDispatcher eventDispatcher, ParsingLoadable<HlsPlaylist> multivariantPlaylistLoadable) { | ||
| long elapsedRealtime = | ||
| initialPlaylistLoader.startLoading( | ||
| multivariantPlaylistLoadable, |
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The requestMasterPlaylist was simply a refactoring (extract method), then call the method in the SntpClient callback. Most times this is a no-op as the SntpClient offset is up to date.
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| private void loadAfterTimeSync(Uri playlistRequestUri) { | ||
| ParsingLoadable.Parser<HlsPlaylist> mediaPlaylistParser = |
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The same refactor lift method to create loadAfterTimeSync(). Here only the primary playlist load needs to possibly refresh SntpClient as the master playlist is only loaded once
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@stevemayhew I think you should rebase this against |
This pull request satisfies the enhancement request #702. For playback longer than a few hours the fix for SntpClient is also required, see pull request #697