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feat(audio): pre-generate next chapter immediately on playback start

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When autoNext is on, kick off prefetchNext() as soon as the current
chapter begins playing (all three success paths in startPlayback).
This gives the full chapter duration as lead time for Kokoro TTS
instead of only the last 10%, making auto-next transitions seamless.

The existing 90%-mark $effect is kept as a fallback for cases where
autoNext is toggled on mid-playback after startPlayback has returned.
This commit is contained in:
Admin
2026-03-04 17:40:27 +05:00
parent cf0c0dfaaf
commit 9f3e895fa8
1 changed files with 37 additions and 3 deletions
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40
ui/src/lib/components/AudioPlayer.svelte
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@@ -15,9 +15,18 @@
* 4. If 404, POST /api/audio/:slug/:n to generate. Drive pseudo progress bar.
* On success, presign again and set audioUrl.
*
* ── Pre-fetch at 90% ─────────────────────────────────────────────────────
* A $derived watches currentTime/duration. When >= 90% and autoNext is on
* and there IS a next chapter, it kicks off prefetchNext():
* ── Pre-fetch (immediate + 90% fallback) ────────────────────────────────
* When autoNext is on, prefetchNext() is called as soon as the current
* chapter starts playing (via maybeStartPrefetch() at the end of
* startPlayback()). This gives the maximum lead time for Kokoro to
* generate the next chapter so the transition is seamless.
*
* A $effect also watches currentTime/duration and fires prefetchNext() at
* the 90% mark as a fallback — covering the case where autoNext was toggled
* on mid-playback after startPlayback() had already returned.
* The nextStatus !== 'none' guard prevents double-runs in all cases.
*
* prefetchNext():
* • Calls POST /api/audio for next chapter (sets nextStatus='prefetching')
* • On success, presigns and stores URL in audioStore.nextAudioUrl
* (sets nextStatus='prefetched')
@@ -268,6 +277,8 @@
audioStore.audioUrl = url;
audioStore.status = 'ready';
// Don't restore saved time for auto-next; position is 0
// Immediately start pre-generating the chapter after this one.
maybeStartPrefetch();
return;
}
@@ -278,6 +289,8 @@
audioStore.status = 'ready';
// Restore last saved position after the audio element loads
restoreSavedAudioTime();
// Immediately start pre-generating the next chapter in background.
maybeStartPrefetch();
return;
}
@@ -299,6 +312,8 @@
audioStore.audioUrl = url2;
audioStore.status = 'ready';
// Don't restore time for freshly generated audio — position is 0
// Immediately start pre-generating the next chapter in background.
maybeStartPrefetch();
} catch (e) {
stopProgress();
audioStore.progress = 0;
@@ -307,6 +322,25 @@
}
}
/**
* Start pre-fetching the next chapter if autoNext is on, there is a next
* chapter, and no prefetch is already running or completed.
* Called as soon as current-chapter playback begins so that the next
* chapter's audio is ready before we need it (seamless transition).
* The 90%-mark $effect acts as a fallback for cases where autoNext is
* toggled on mid-playback.
*/
function maybeStartPrefetch() {
if (
audioStore.autoNext &&
nextChapter !== null &&
nextChapter !== undefined &&
audioStore.nextStatus === 'none'
) {
prefetchNext();
}
}
/**
* Fetch the saved audio time for this chapter and seek to it after a short
* delay (to allow the audio element to load the source).