Probe `/tmp/expbuf_probe.c` (snapshot at probes/expbuf_probe.c) opens
/dev/video1, sets OUTPUT format H264_SLICE 1920x1088, REQBUFS 4 capture
buffers, EXPBUF on plane 0 of buffer 0, lseek(fd, 0, SEEK_END).
On ohm (kernel besser-7.0, hantro-vpu / rk3568-vpu-dec):
CAPTURE: NV12 1920x1088 num_planes=1 sizeimage=3655712
EXPBUF fd lseek(SEEK_END) = 3657728 (page-rounded from 3655712)
Kernel exports the dma_buf at full sizeimage; offset 2,088,960
(plane 1 base in ffmpeg's drm-frame-descriptor) is well inside.
Hantro is innocent.
Side observation: sizeimage = 3,655,712 > naive NV12's 3,133,440.
The 522,272-byte excess is trailing padding (likely Rockchip
per-frame MV / context metadata) past the UV plane. Y and UV layout
fit cleanly within [0, 3,133,440), exactly where mpv/ffmpeg expect.
Remaining hypothesis space: H1 (panfrost EGL non-zero plane offset),
H2 (KWin wl_dmabuf import), H4 (kwin-fourier residual, low conf).
Next probe queued: H2 source-read of KWin 6.6.4 wl_dmabuf import
path. ~30 min, no hardware needed. If that turns up nothing,
write the EGL importer harness for H1.
Posted to dmabuf-modifier-triage#1 comment 255.
