FFmpeg 8.x dropped the H.264 decoder's low_delay code path —
AV_CODEC_FLAG_LOW_DELAY no longer prevents h264_select_output_frame
from running the display-order DPB output queue. The daedalus-v4l2
daemon's `ctx->flags |= AV_CODEC_FLAG_LOW_DELAY` at
daemon/src/decoder.c:202 has been a silent no-op since the SONAME
61→62 jump landed in reauktion/daedalus-v4l2 PR #16; on Firefox
YouTube this re-introduced the 2-1-4-3 B-frame pair-swap that PR
#12's daemon flag was supposed to prevent.
Fix lives in libavcodec, not the daemon: restore the documented
LOW_DELAY semantics so the daemon (and any other V4L2-stateless-
style consumer) keeps the one-frame-per-send_packet decode-order
output contract it already declares.
## Patch
0006-h264-restore-low-delay.patch touches libavcodec/h264_slice.c:
- h264_select_output_frame: early-exit when LOW_DELAY is set.
Emit the just-decoded picture as next_output_pic, mirror the
corruption / recovery-point tracking the main path performs,
skip delayed_pic[] / POC reorder machinery entirely.
- h264_field_start: suppress the SPS-driven
`has_b_frames = sps->num_reorder_frames` clobber when LOW_DELAY
is set. Without this the per-slice bitstream_restriction_flag
re-pickup would reintroduce a nonzero reorder buffer mid-stream
even after the daemon set has_b_frames=0 at avcodec_open2.
## Why not daemon-side
A daemon SPS-rewrite (`num_reorder_frames=0`) was considered but
rejected: it works only for the daemon's reconstructed SPS NAL,
not for any in-band SPS the daemon dlopens libavformat to parse
in other code paths. Restoring documented FFmpeg flag semantics
is the smaller, more durable change and keeps the daemon
interface stable.
## Packaging
- PKGREL/pkgrel bump to 9.
- No new build-deps, no Depends change.
- Substitution arc cycles 6/7/8 unchanged.
## Refs
- reauktion/daedalus-v4l2#11 / #12 (LOW_DELAY half-measure on
daemon side, originally landed against FFmpeg 7.x).
- daemon/src/decoder.c:202 (`ctx->flags |= AV_CODEC_FLAG_LOW_DELAY`
for H.264 only — unchanged, but now actually has effect again).
