[x264-devel] Regarding horizontal and vertical range of motion vectors.

[Panagiotis Issaris]

Hi Mahesh,

mahesh k schreef:
> Hi all,
> 
> Can any one please tell me whats the need of having different horizontal and
> vertical ranges for motion vector components in H.264 . Also the horizontal
> ranges are independent of levels but the vertical ranges depend on level of
> the decoder ?
> 
> I am working on H.264 decoder (Constrained to only baseline profile).
> Please tell me how to handle the motion vectors if they point to a
> Macroblock outside the frame boundary.?

AFAIK, if they point left or right of the frame boundary, you have to
replicate the pixels on the border, so, if this would be a block at the
extreme right of the frame, right at the border:
45 34 37 40 |
34 33 45 46 |
12 13 34 35 |
43 44 46 59 |

This would become something like this:
45 34 37 40 | 40 40 40 ...
34 33 45 46 | 46 46 46 ...
12 13 34 35 | 35 35 35 ...
43 44 46 59 | 59 59 59 ...

Similar for a motion vector pointing above or below the frame boundary.

I'm pretty sure about this for luma, less sure for chroma...

And, unfortunately, I'm not sure yet what happens for motion vectors
pointing outside the corners of the frame.


And just as it might help you in the future: There's two mailinglist
which are not about a specific H.264 encoder but are more about
MPEG-4/H.264 in general: mp4-tech[1] and jvt-experts[2].

With friendly regards,
Takis
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[1] http://lists.mpegif.org/mailman/listinfo/mp4-tech
[2] http://mailman.rwth-aachen.de/mailman/listinfo/jvt-experts