[FFmpeg-devel] [PATCH]lavc/h264:Only check x264_build if it was set

[Henrik Gramner]

On Thu, Oct 5, 2017 at 8:31 AM, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> Hi!
>
> Attached patch fixes ticket #6717.
>
> Please comment, Carl Eugen

Signed numbers are converted to unsigned when compared to unsigned
numbers which means -1 becomes UINT_MAX so this patch shouldn't
actually change anything.

#6717 is probably unfixable without breaking something else. Old x264
versions produced non-spec-compliant output in the case of 4:4:4 +
cabac + 8x8dct, and old libavcodec versions had the same bug on the
decoder side which is now fixed to handle spec-compliant files.

libavcodec supports decoding older broken files when it detects them
in order to avoid breaking backwards-compatibility, but they can't be
detected as such if someone removed the x264 SEI.

tl;dr; #6717 is one of the reasons why messing with SEI messages is
generally a bad idea unless you know what you're doing.