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Code Issues Releases Activity

avcodec/mpegpicture: Always reset motion val buffer

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Codecs call ff_find_unused_picture() to get the index of
an unused picture; said picture may have buffers left
from using it previously (these buffers are intentionally
not unreferenced so that it might be possible to reuse them;
this is mpegvideo's version of a bufferpool). They should
not make any assumptions about which picture they get.
Yet somehow this is not true when decoding OBMC: Returning
random empty pictures (instead of the first one) leads
to nondeterministic results; similarly, explicitly
rezeroing the buffer before handing it over to the codec
changes the outcome of the h263-obmc tests, but it makes it
independent of the returned pictures. Therefore this commit
does so.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2022-08-08 16:51:04 +02:00
parent caac9740f8
commit 71ff9217f7
1 changed files with 4 additions and 0 deletions
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4
libavcodec/mpegpicture.c
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@ -245,6 +245,10 @@ int ff_alloc_picture(AVCodecContext *avctx, Picture *pic, MotionEstContext *me,
for (i = 0; i < 2; i++) {
pic->motion_val[i] = (int16_t (*)[2])pic->motion_val_buf[i]->data + 4;
pic->ref_index[i] = pic->ref_index_buf[i]->data;
/* FIXME: The output of H.263 with OBMC depends upon
* the earlier content of the buffer; therefore we
* reset it here. */
memset(pic->motion_val_buf[i]->data, 0, pic->motion_val_buf[i]->size);
}
}