fix: fix position jump on playback rate change #4268
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| private bufferNode: AudioBufferSourceNode | null = null | ||
| private playStartTime = 0 | ||
| private playedDuration = 0 | ||
| private playbackPosition = 0 |
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Renamed playedDuration to playbackPosition to clarify that this variable represents a coordinate (offset) within the audio buffer, rather than elapsed wall-clock time.
| this.bufferNode.connect(this.gainNode) | ||
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| let currentPos = this.playedDuration * this._playbackRate | ||
| let currentPos = this.playbackPosition |
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Since playbackPosition now denotes the absolute position in the buffer, it is used directly as the starting offset without any rate-based scaling.
| this.paused = true | ||
| this.bufferNode?.stop() | ||
| this.playedDuration += this.audioContext.currentTime - this.playStartTime | ||
| this.playbackPosition += (this.audioContext.currentTime - this.playStartTime) * this._playbackRate |
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Upon pausing, the wall-clock time elapsed since the last play start is multiplied by the playbackRate to calculate the actual "distance" covered in the track, which is then accumulated into playbackPosition.
| const wasPlaying = !this.paused | ||
| if (wasPlaying) this._pause() | ||
| this._playbackRate = value | ||
| if (wasPlaying) this._play() | ||
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By calling _pause() before a rate change, we "snapshot" the current position as a buffer offset. Resuming with _play() ensures continuity in time calculation, preventing cursor jumps.
| return this.paused | ||
| ? this.playbackPosition | ||
| : this.playbackPosition + (this.audioContext.currentTime - this.playStartTime) * this._playbackRate |
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During playback, it returns the fixed starting point (playbackPosition) plus the real-time distance (elapsed time * rate). This prevents past accumulated data from being corrupted by the current rate setting.
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| if (wasPlaying) this._pause() | ||
| this.playedDuration = value / this._playbackRate | ||
| this.playbackPosition = value |
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The user-defined seek target (value) is an absolute value in seconds, so it is assigned directly to playbackPosition regardless of the playback rate.
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@katspaugh Could you review this PR? |
2 participants
Short description
This PR fixes a bug where currentTime returns an incorrect value when playbackRate is modified, causing the progress tracking to jump abnormally.
Implementation details
How to test it
Screenshots
Here are videos changing playback rate dynamically:
Before:
2025-12-21.062929.mp4
After:
2025-12-21.062805.mp4
Checklist