[FFmpeg-devel] H.261 chroma motion vector rounding.

[Hendrik Leppkes]

On Sun, Apr 2, 2017 at 10:33 PM, Christina Brien
<christina.brien at polygonindustrial.com> wrote:
> Hi
>
> Having written a clean-room implementation of H.261 and comparing it to the output of FFMPEG, I have found that FFMPEG is not spec-compliant with regard to negative chroma motion vectors. The spec states that chroma motion vectors are the luma motion vectors divided by two, and rounded *towards zero*. FFMPEG currently rounds towards negative infinity.
>
> This patch makes FFMPEG compliant, but breaks the regression tests.
>

C integer divison truncates, that equals rounding towards zero.

- Hendrik