The browser-side WebRTC reproductor needs MP4 / H.264 / AAC / yuv420p to
keep MSE happy. This package decides per request whether to:
• direct-play — input already MSE-compatible, just remux to fMP4
• transcode — re-encode video (libx264 / NVENC / QSV / VAAPI /
VideoToolbox) + audio (AAC), fragment to fMP4
Pieces:
- internal/streaming/transcoder.go — AnalyzeCompatibility decides the
recipe from a parsed mediainfo. CompatibilityReport carries the reasons
so the player UI can show "transcoding video: HEVC → H.264".
- internal/streaming/ffmpeg_args.go — BuildFFmpegArgs assembles the argv
for ffmpeg. Direct play uses `-c copy`; transcode uses libx264 or the
selected HW encoder. Output is always fragmented MP4 piped to stdout
(-movflags frag_keyframe+empty_moov+default_base_moof) so the HTTP
handler can stream straight to the browser without disk I/O.
Quality ladder: 480p (1.5Mb), 720p (3.5Mb), 1080p (6Mb), 2160p (25Mb).
Default 1080p when unset / unknown. -ss seek for resume / scrubbing.
- internal/streaming/hwaccel.go — DetectHWAccel runs `ffmpeg -encoders`
once per process and caches the best available. Order: NVENC → QSV →
VAAPI → VideoToolbox → libx264. VAAPI is the only family that wires up
HW decode too (`-hwaccel vaapi`); the others software-decode and HW-
encode (works fine and avoids /dev/dri permission rabbit holes).
- internal/streaming/stream.go — Transcoder facade wires Analyze + Stream
together for the API handler in Fase 4. Captures the last 8 KiB of
ffmpeg stderr for diagnosable errors without unbounded memory.
Tests (20 unit, all green):
- AnalyzeCompatibility: h264+aac direct, video-only direct, HEVC →
transcode, 10-bit HDR → transcode, EAC3 audio → transcode, nil guards
- ResolveQuality: empty + unknown fallback to 1080p, 4-step ladder
- BuildFFmpegArgs: direct play -c copy, transcode libx264 + bitrate +
scale, NVENC swaps encoder & drops preset, VAAPI injects -hwaccel +
scale_vaapi, -ss timestamp formatting
- HWAccel: encoder-name table, VAAPI is the only one with HW decode
- formatDuration: zero, sub-second, HH:MM:SS, negative-clamped
- cappedBuffer: tail retention through multi-write and large-write paths
- NewTranscoder: rejects empty paths
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