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feat(transcode): dynamic H.264 level + HW probe + capability reporting

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Three related fixes around 4K-source transcoding that left the web
player stuck on "preparing session" with no useful diagnostics:

1. Dynamic -level:v derived from output height (hls.go, transcoder.go).
   The previous fixed "4.0" silently rejected anything taller than 1080p
   inside libx264 — "frame MB size > level limit", "DPB size > level
   limit" — and emitted unplayable segments. Helper H264LevelForHeight()
   now picks 4.0 / 5.0 / 5.1 / 6.0 from the actual encode height.

2. New `unarr probe-hwaccel` diagnostic command. Lists the HW encoders
   compiled into ffmpeg, the device files / drivers present, and the
   backend the daemon would actually pick today. Surfaces the canonical
   gotcha: a host with an RTX 3090 + nvidia-smi but a Homebrew ffmpeg
   built without --enable-nvenc still falls back to libx264 software.

3. Register payload now includes hwAccel + maxTranscodeHeight so the web
   side can suggest a smaller alternate quality before the user even
   tries to play a 4K source on a software-only host. Software-only =
   1080p cap, any HW backend = 2160p cap.
This commit is contained in:
Deivid Soto 2026-05-08 15:57:02 +02:00
parent 01941ed2e4
commit 209ea38ecf
9 changed files with 297 additions and 30 deletions
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12
internal/engine/transcoder.go
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@ -25,6 +25,7 @@ type TranscodeOpts struct {
VideoBitrate string // e.g. "5M"
AudioBitrate string // e.g. "192k"
MaxHeight int // optional downscale cap (e.g. 720)
SourceHeight int // probed source height — used to derive a sane H.264 level
StartSeconds float64
FFmpegPath string
}
@ -235,7 +236,16 @@ func buildFFmpegArgs(filePath string, opts TranscodeOpts) []string {
// can fail with "VaapiWrapper: failed initializing" on Linux boxes
// where VA-API isn't fully wired up. `main` keeps a clean software
// decode fallback on every desktop + mobile platform.
args = append(args, "-profile:v", "main", "-level:v", "4.0")
//
// Level is derived from the actual output height — a fixed "4.0"
// silently rejects 4K and 1440p sources at the libx264 macroblock
// limits and produces unplayable streams. opts.MaxHeight is the
// downscale cap when set; falling through means "encode at source".
levelHeight := opts.MaxHeight
if levelHeight == 0 || (opts.SourceHeight > 0 && opts.SourceHeight < levelHeight) {
levelHeight = opts.SourceHeight
}
args = append(args, "-profile:v", "main", "-level:v", H264LevelForHeight(levelHeight))
args = append(args, "-b:v", coalesce(opts.VideoBitrate, "5M"))
// Filter chain:
// 1. scale (optional) — cap height + force even width.