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Code Issues Releases Activity

avcodec/snowenc: fix SIGFPE in get_dc() when a block lies outside the plane

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get_dc() divides the accumulated, OBMC-weighted DC by aa, the sum of the
squared OBMC weights taken over the in-plane pixels.  When an OBMC block
falls entirely outside the plane - e.g. a tiny chroma plane after mcdeint
splits a frame into fields - no pixel contributes, aa stays 0 and the
ROUNDED_DIV() divides by zero (SIGFPE).  ab is 0 in exactly the same case,
so the result degenerates to 0; return it directly.

Reproducible with the GPL mcdeint filter in slow/extra_slow mode, e.g.

    ffmpeg -f lavfi -i testsrc=s=128x2 -vf mcdeint=mode=slow -f null -

Add a self-contained lavfi-based FATE regression test for the slow mode,
which previously crashed and is therefore not covered by the existing
sample-based fast/medium tests.

Fixes trac ticket #7779.

Signed-off-by: Bogdan Lisman <bogdan@pydevsolutions.com>
This commit is contained in:
Bogdan Lisman
2026-06-15 03:24:14 +03:00
committed by Michael Niedermayer
parent 30c6667dad
commit a62d996927
3 changed files with 14 additions and 0 deletions
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libavcodec/snowenc.c
+3
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@@ -725,6 +725,9 @@ static int get_dc(SnowEncContext *enc, int mb_x, int mb_y, int plane_index)
}
*b= backup;
if (!aa)
return 0;
return av_clip_uint8( ROUNDED_DIV((int64_t)ab<<LOG2_OBMC_MAX, aa) ); //FIXME we should not need clipping
}
tests/fate/filter-video.mak
+3
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@@ -54,6 +54,9 @@ FATE_FILTER_SAMPLES-$(call FILTERDEMDEC, MCDEINT, MPEGTS, MPEG2VIDEO, SNOW_ENCOD
FATE_FILTER-$(call FILTERFRAMECRC, MCDEINT TESTSRC, SNOW_ENCODER) += fate-filter-mcdeint-slow-edge
fate-filter-mcdeint-slow-edge: CMD = framecrc -auto_conversion_filters -flags bitexact -lavfi testsrc=s=5x32:r=25:d=1,mcdeint=mode=slow -frames:v 3
FATE_FILTER-$(call FILTERFRAMECRC, MCDEINT TESTSRC, SNOW_ENCODER) += fate-filter-mcdeint-slow
fate-filter-mcdeint-slow: CMD = framecrc -auto_conversion_filters -flags bitexact -lavfi testsrc=s=128x2:r=25:d=1,mcdeint=mode=slow -frames:v 3
FATE_FILTER_SAMPLES-$(call FILTERDEMDEC, CODECVIEW, RM, RV40) += fate-filter-codecview-mvs
fate-filter-codecview-mvs: CMD = framecrc -flags2 +export_mvs -i $(TARGET_SAMPLES)/real/spygames-2MB.rmvb -vf codecview=mv=pf+bf+bb -frames:v 60 -an
tests/ref/fate/filter-mcdeint-slow
+8
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@@ -0,0 +1,8 @@
#tb 0: 1/25
#media_type 0: video
#codec_id 0: rawvideo
#dimensions 0: 128x2
#sar 0: 1/1
0, 0, 0, 1, 768, 0x6d637c68
0, 1, 1, 1, 768, 0x07867cb0
0, 2, 2, 1, 768, 0xa1ef7d04