Add support for writing Unix epoch-relative tracks to HLS, add proper cleanup of all Targets obtained by an Output

src/flac/flac-demuxer.ts

@@ -598,7 +598,7 @@ class FlacAudioTrackBacking implements InputAudioTrackBacking {
 		return this.demuxer.audioInfo.sampleRate;
 	}
 
-	getTimestampsAreRelativeToUnixEpoch() {
+	isRelativeToUnixEpoch() {
 		return false;
 	}