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feat(stream): bitrate-sized readahead for play-while-download

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The torrent reader used a static 5 MiB readahead — about 1.9s of a 20 Mbps 4K
stream — so streaming a torrent while it downloaded outran the download and
stalled. anacrolix's reader already prioritises the pieces in the readahead
window ahead of the playhead (and re-prioritises on seek); the window was just
too small. dynamicReadahead sizes it to ~30s of video (clamped 8-96 MiB, 24 MiB
default when bitrate is unknown). The torrent provider probes the bitrate
asynchronously so stream start never blocks on ffprobe; readers created after
the probe resolves pick up the accurate size. Real 4K (20.7 Mbps) -> 73 MiB.
This commit is contained in:
Deivid Soto 2026-05-31 23:23:39 +02:00
parent e4373454ba
commit 9c995fc4dd
6 changed files with 110 additions and 6 deletions
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4
internal/engine/stream.go
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@ -235,7 +235,9 @@ func (s *StreamEngine) WaitBuffer(ctx context.Context, progressFn func(buffered,
func (s *StreamEngine) NewFileReader(ctx context.Context) io.ReadSeekCloser {
reader := s.file.NewReader()
reader.SetResponsive()
reader.SetReadahead(5 * 1024 * 1024) // 5MB readahead
// Generous default window (vs the old static 5 MiB that stalled HD/4K). This
// CLI path has no bitrate probe, so dynamicReadahead(0) returns the default.
reader.SetReadahead(dynamicReadahead(0))
reader.SetContext(ctx)
return reader
}