Hi,
On Tue, Oct 9, 2012 at 4:56 PM, Mashiat Sarker Shakkhar
<mashiat.sar...@gmail.com> wrote:
> On 10/9/2012 7:37 PM, Ronald S. Bultje wrote:
>>
>> Hi,
>>
>> On Tue, Oct 9, 2012 at 1:38 PM, Mashiat Sarker Shakkhar
>> <mashiat.sar...@gmail.com> wrote:
>>>
>>> This is required due to the way VC-1 handles chroma pull-back which may
>>> end
>>> up causing negative chroma MV for zero luma MV. Edge emulation needs to
>>> be
>>> invoked in such cases.
>>>
>>> This problem only affects chroma Y motion vector.
>>> ---
>>> libavcodec/vc1dec.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavcodec/vc1dec.c b/libavcodec/vc1dec.c
>>> index 42eb4a5..2683c86 100644
>>> --- a/libavcodec/vc1dec.c
>>> +++ b/libavcodec/vc1dec.c
>>> @@ -430,7 +430,7 @@ static void vc1_mc_1mv(VC1Context *v, int dir)
>>> if (v->rangeredfrm || (v->mv_mode == MV_PMODE_INTENSITY_COMP)
>>> || s->h_edge_pos < 22 || v_edge_pos < 22
>>> || (unsigned)(src_x - s->mspel) > s->h_edge_pos - (mx&3) - 16 -
>>> s->mspel * 3
>>> - || (unsigned)(src_y - s->mspel) > v_edge_pos - (my&3) - 16 -
>>> s->mspel * 3) {
>>> + || (unsigned)(src_y - 1) > v_edge_pos - (my&3) - 16 -
>>> 3) {
>>
>>
>> I'm slightly curious why this is only the case for the vertical
>> dimension, but not the horizontal. Is that intentional, or an
>> oversight?
>
>
> This thread contains my earlier discussion on a rejected patch which tried
> to fix the same bug:
>
> http://patches.libav.org/patch/26240/
OK so it's not because of pullback per se, but because of field
adjustment, then it makes sense.
Ronald
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