[FFmpeg-devel] [PATCH] avcodec/vc1: fix B predictor validity for 4-MV MBs

[Carl Eugen Hoyos]

2019-01-14 13:05 GMT+01:00, Jerome Borsboom <jerome.borsboom at carpalis.nl>:
>> 2019-01-14 9:05 GMT+01:00, Jerome Borsboom <jerome.borsboom at
>> carpalis.nl>:
>>> The B predictor for 4-MV MBs in interlace field pictures is not used
>>> for blocks 0 and 2 when the picture is 1 MB wide.
>>>
>>> Signed-off-by: Jerome Borsboom <jerome.borsboom at carpalis.nl>
>>> ---
>>> My 'shuffle calculation of MV predictor candidates' patch overlooked the
>>> corner case of 1 MB wide field interlace pictures. According to VC-1 spec
>>> and the reference decoder, the B predictor is not used for for block 0
>>> and
>>> block 2 when the picture is 1 MB wide. This patch corrects this.
>>>
>>>  libavcodec/vc1_pred.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/libavcodec/vc1_pred.c b/libavcodec/vc1_pred.c
>>> index e1758a3817..77dda86cd0 100644
>>> --- a/libavcodec/vc1_pred.c
>>> +++ b/libavcodec/vc1_pred.c
>>> @@ -289,6 +289,8 @@ void ff_vc1_pred_mv(VC1Context *v, int n, int dmv_x,
>>> int
>>> dmv_y,
>>>          case 3:
>>>              off = -1;
>>>          }
>>> +        if (v->field_mode && s->mb_width == 1)
>>> +            b_valid = b_valid && c_valid;
>>
>> I will push this if you don't request commit rights
>> but shouldn't this be "b_valid &= c_valid;"?
>
> Please push.

Patch applied.

Thank you, Carl Eugen