Adds a brute-force fallback to v4l2request_open_decoder() that
enumerates /dev/media[0..15] and /dev/video[0..63] directly when
udev_enumerate_scan_devices() returns an error. The fallback uses
absolute paths only (no fd-relative openat), which is what makes it
work inside firefox's RDD seccomp+broker sandbox where Mozilla's
OpenAtTrap rejects fd-relative paths used by systemd's chase()
symlink resolver.
Same approach Chromium uses in media/gpu/v4l2/stateless/ on ChromeOS,
where the sandbox similarly forbids libudev's chase pattern.
No regression: the libudev path runs first and the brute-force path
only activates on its failure. AV_LOG_INFO line announces the
fallback so it's visible in MOZ_LOG=FFmpegLib:5.
Validated on RK3399 / Pinebook Pro / rkvdec:
libudev probe failed (-2), falling back to brute-force /dev/media*
Using V4L2 media driver rkvdec (brute-force) for S264
Reinit context to 1920x1088, pix_fmt: drm_prime
RDD CPU = 4.9%
Bumps pkgrel=2. Worth submitting to Kwiboo's fork upstream.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
