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fix(stream): derive H.264 level from frame macroblocks, not height

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Anamorphic 2.39:1 scaled to 1080 height = ~2586x1080 = 11016 MBs, busting
level 4.1's 8192-MB MaxFS -> nvenc "InitializeEncoder failed: Invalid Level"
(libx264: "frame MB size > level limit") -> 0 segments, session stalls. Most
4K rips are 2.39:1, so HLS playback was silently broken for them.

H264LevelForFrame(w,h) derives the level from the real macroblock count
(max of MB-tier and height-tier). hls.go computes output width and uses it.
16:9 unchanged; anamorphic bumps to 5.0 when needed. Discovered + verified
during the trickplay smoke.
This commit is contained in:
Deivid Soto 2026-06-01 08:29:10 +02:00
parent ea00130d08
commit 8accafbe59
3 changed files with 107 additions and 12 deletions
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20
internal/engine/hls.go
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@ -22,6 +22,7 @@ import (
"fmt"
"io"
"log"
"math"
"net/http"
"os"
"os/exec"
@ -1184,11 +1185,14 @@ func buildHLSFFmpegArgsAt(cfg HLSSessionConfig, probe *StreamProbe, tmpDir strin
// per session start, polluting logs even though encode succeeds.
args = append(args, "-vaapi_device", "/dev/dri/renderD128")
}
// Derive H.264 level from the actual output height. A fixed "4.0" caps the
// encoder at 1080p — anything taller (1440p, 4K source on quality=original)
// fails libx264 with "frame MB size > level limit" and emits unplayable
// segments. The output height matches qcap.MaxHeight when the source is
// downscaled, otherwise probe.Height (already populated by ffprobe).
// Derive H.264 level from the actual output FRAME (width × height), not just
// height. A fixed "4.0" caps the encoder at 1080p; deriving by height alone
// still under-levels anamorphic content — a 2.39:1 source scaled to 1080
// height is ~2586×1080 = 11016 MBs, busting level 4.1's 8192-MB cap, which
// fails the encode ("Invalid Level" on nvenc, "frame MB size > level limit"
// on libx264) and stalls the session. The output height matches qcap.MaxHeight
// when the source is downscaled, otherwise probe.Height; the output width is
// the source width scaled by the same factor (the filter chain preserves AR).
qcap := resolveQualityCap(cfg.Quality)
outputHeight := qcap.MaxHeight
if outputHeight == 0 {
@ -1197,7 +1201,11 @@ func buildHLSFFmpegArgsAt(cfg HLSSessionConfig, probe *StreamProbe, tmpDir strin
if outputHeight == 0 || (probe.Height > 0 && probe.Height < outputHeight) {
outputHeight = probe.Height
}
args = append(args, "-profile:v", "main", "-level:v", H264LevelForHeight(outputHeight))
outputWidth := probe.Width
if probe.Height > 0 && outputHeight != probe.Height {
outputWidth = int(math.Round(float64(probe.Width) * float64(outputHeight) / float64(probe.Height)))
}
args = append(args, "-profile:v", "main", "-level:v", H264LevelForFrame(outputWidth, outputHeight))
// Bitrate must match the level libx264 actually picks for outputHeight,
// not the qcap target for the user's requested label. If a user asks for