#10669: crop filter with exact=0 does not work correctly on
non-chroma-subsampled
hardware-backed inputs
-------------------------------------+-------------------------------------
Reporter: Russell | Type: defect
Status: new | Priority: normal
Component: avfilter | Version: git-
Keywords: crop vaapi | master
hwaccel | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Summary of the bug: I'm trying to crop a 444 (no chroma subsampling) video
using `crop` using vaapi. The crop region seems to always be rounded to a
multiple of two, even though the input has no chroma subsampling, which
according to the documentation means that `exact` should have no effect.
Originally reported to a project I develop at https://github.com/russelltg
/wl-screenrec/issues/26
The sample video has lines at x,y = 100,299. So the crop args
w=200:h=200:x=100:x=100 should give a perfect box around the corner (which
it does). But w=200:h=200:x=101:x=101 incorrectly gives the same result.
How to reproduce:
{{{
% ffmpeg -vaapi_device /dev/dri/renderD129 -i screenrecord.mp4 -vf
'hwupload,
crop=w=200:h=200:x=101:y=101,scale_vaapi=format=nv12:w=200:h=200' -c:v
h264_vaapi cropped.mp4
ffmpeg version N-112783-g5452cbdc15
built with gcc 13.2.1 (GCC) 20230801
HW: Intel i9-11900H
}}}
However, it does work if you put exact=1
It seems to me that the problematic snippet is from vf_crop.c:158
{{{
if (pix_desc->flags & AV_PIX_FMT_FLAG_HWACCEL) {
s->hsub = 1;
s->vsub = 1;
} else {
s->hsub = pix_desc->log2_chroma_w;
s->vsub = pix_desc->log2_chroma_h;
}
}}}
from vf_crop.c, which seems to assume all hardware backed formats have 2x2
chroma subsampling (which, sure is typically the case, but not always!)
--
Ticket URL: <https://trac.ffmpeg.org/ticket/10669>
FFmpeg <https://ffmpeg.org>
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