feat(stream): burn bitmap (PGS/DVB) subtitles into the video via overlay
Bitmap subs can't be served as WebVTT, so the user picks one and the daemon
re-encodes with it overlaid. HLSSessionConfig.BurnSubtitleIndex (*int, nil=no
burn) flows into the cache key + a -filter_complex graph:
[0✌️0]<vchain>[base];[0:s:N][base]scale2ref[sub][base2];[base2][sub]overlay[vout]
Overlay after the tonemap (SDR subs keep brightness); scale2ref fits the PGS
canvas to the output. Invalid/text/out-of-range index -> clean-encode fallback.
IsTextSubtitle now includes "text" (parity with the web classifier).
This commit is contained in:
Deivid Soto
parent
8207d1d2a9
commit
665ec0a34f
9 changed files with 196 additions and 49 deletions
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@ -151,7 +151,15 @@ type HLSSessionConfig struct {
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FileName string
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Quality string // "2160p"|"1080p"|"720p"|"480p"|"original"|""
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AudioIndex int // 0-based ffmpeg audio stream selection (-map 0:a:N). -1 = default.
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Transcode TranscodeRuntime
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// BurnSubtitleIndex burns a BITMAP subtitle (PGS/DVB) at this 0-based
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// subtitle stream index into the video. nil = no burn (text subs are served
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// as separate WebVTT). A pointer (not int) so the zero value 0 — a valid
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// stream index — can't be mistaken for a burn request when a caller leaves
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// the field unset. Part of the cache key so a burned encode never collides
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// with the clean one. Forces the video re-encode the HLS path already does
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// to also composite the subtitle overlay.
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BurnSubtitleIndex *int
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Transcode TranscodeRuntime
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// Cache is an optional persistent segment cache keyed by (source, quality,
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// audio). When set, completed encodes are kept across sessions so re-plays
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// of the same file at the same quality skip ffmpeg entirely. nil disables
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@ -169,6 +177,15 @@ func (cfg HLSSessionConfig) sourceRef() string {
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return cfg.SourcePath
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}
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// burnSubtitleIndexOrNone resolves the optional burn-in subtitle pointer to the
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// int sentinel the cache key and filtergraph use: nil → -1 ("no burn").
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func (cfg HLSSessionConfig) burnSubtitleIndexOrNone() int {
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if cfg.BurnSubtitleIndex == nil {
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return -1
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}
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return *cfg.BurnSubtitleIndex
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}
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// logName is a short, log-friendly source label. For local files it's the base
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// name; for a URL source (no SourcePath) it prefers FileName over the raw URL
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// (which would leak a query-string token into the logs).
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@ -383,9 +400,9 @@ func StartHLSSession(ctx context.Context, cfg HLSSessionConfig) (*HLSSession, er
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// Debrid URL sessions key by CacheID (info_hash) so re-plays hit cache
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// despite the URL changing each resolution; local files key by path.
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if cfg.CacheID != "" {
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cacheKey = cfg.Cache.KeyForID(cfg.CacheID, cfg.Quality, cfg.AudioIndex)
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cacheKey = cfg.Cache.KeyForID(cfg.CacheID, cfg.Quality, cfg.AudioIndex, cfg.burnSubtitleIndexOrNone())
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} else {
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cacheKey = cfg.Cache.KeyFor(cfg.SourcePath, cfg.Quality, cfg.AudioIndex)
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cacheKey = cfg.Cache.KeyFor(cfg.SourcePath, cfg.Quality, cfg.AudioIndex, cfg.burnSubtitleIndexOrNone())
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}
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// Integrity gate: HasComplete just stats the marker. If init.mp4 or
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// the last segment vanished (external rm, partial-disk failure), we
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@ -1217,8 +1234,31 @@ func buildHLSFFmpegArgsAt(cfg HLSSessionConfig, probe *StreamProbe, tmpDir strin
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args = append(args, "-output_ts_offset", strconv.FormatFloat(startSec, 'f', 3, 64))
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}
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// Map video + selected audio. Always use first video stream.
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args = append(args, "-map", "0:v:0")
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// Burn a bitmap subtitle (PGS/DVB) into the video when requested. Validate
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// the index points at a real bitmap track in range — text subs are served as
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// separate WebVTT and never burned, and a stale/out-of-range index falls
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// back to a clean encode rather than failing the session.
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burnIdx := -1
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if reqBurn := cfg.burnSubtitleIndexOrNone(); reqBurn >= 0 {
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if reqBurn < len(probe.SubtitleTracks) &&
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!probe.SubtitleTracks[reqBurn].IsTextSubtitle() {
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burnIdx = reqBurn
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} else {
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log.Printf("[hls %s] burn subtitle %d ignored — not a bitmap track in range",
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shortHLSID(cfg.SessionID), reqBurn)
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}
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}
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// Map video + selected audio. With burn-in the video comes from the
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// filter_complex graph ([vout], built below); otherwise map the source video
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// stream directly. ffmpeg resolves the [vout] label from -filter_complex
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// regardless of argv order, so mapping it here (before audio) keeps video as
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// output stream 0.
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if burnIdx >= 0 {
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args = append(args, "-map", "[vout]")
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} else {
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args = append(args, "-map", "0:v:0")
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}
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audioIdx := cfg.AudioIndex
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if audioIdx < 0 {
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audioIdx = 0
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@ -1362,19 +1402,37 @@ func buildHLSFFmpegArgsAt(cfg HLSSessionConfig, probe *StreamProbe, tmpDir strin
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if probe.HDR != "" && cfg.Transcode.TonemapHDR {
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tonemap = hdrTonemapChain
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}
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var filterChain string
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// Core video chain (scale + optional tonemap + pixel format + color metadata),
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// WITHOUT the optional hwUploadTail — that has to run last, after any subtitle
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// overlay, so it's appended separately below.
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var vchain string
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if maxH > 0 && probe.Height > maxH {
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filterChain = fmt.Sprintf(
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"scale=-2:%d:force_original_aspect_ratio=decrease,scale=trunc(iw/2)*2:trunc(ih/2)*2,%sformat=%s%s%s",
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maxH, tonemap, pixFormat, colorTail, hwUploadTail,
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vchain = fmt.Sprintf(
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"scale=-2:%d:force_original_aspect_ratio=decrease,scale=trunc(iw/2)*2:trunc(ih/2)*2,%sformat=%s%s",
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maxH, tonemap, pixFormat, colorTail,
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)
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} else {
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filterChain = fmt.Sprintf(
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"scale=trunc(iw/2)*2:trunc(ih/2)*2,%sformat=%s%s%s",
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tonemap, pixFormat, colorTail, hwUploadTail,
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vchain = fmt.Sprintf(
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"scale=trunc(iw/2)*2:trunc(ih/2)*2,%sformat=%s%s",
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tonemap, pixFormat, colorTail,
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)
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}
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args = append(args, "-vf", filterChain)
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if burnIdx >= 0 {
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// Burn-in: process the video to its final size + SDR colorspace FIRST,
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// then composite the subtitle. Overlaying SDR PGS/DVB graphics onto a
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// still-HDR (PQ) frame and tonemapping afterwards would crush the
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// subtitle brightness, so the overlay must come after the tonemap. The
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// subtitle canvas is scaled to the processed frame via scale2ref so a
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// PGS/DVB stream authored at any resolution lines up. hwUploadTail
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// (VAAPI) runs last, on the composited frame.
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filterComplex := fmt.Sprintf(
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"[0:v:0]%s[base];[0:s:%d][base]scale2ref[sub][base2];[base2][sub]overlay%s[vout]",
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vchain, burnIdx, hwUploadTail,
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)
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args = append(args, "-filter_complex", filterComplex)
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} else {
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args = append(args, "-vf", vchain+hwUploadTail)
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}
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// Audio: AAC stereo 48 kHz — broadest browser compatibility.
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audioBitrate := cfg.Transcode.AudioBitrate
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