[x264-devel] Bug#667573: x264: 10 bit builds

[Sebastian Dröge]

On Mi, 2013-01-16 at 16:45 +0100, Nicolas George wrote:
> Le septidi 27 nivôse, an CCXXI, Sebastian Dröge a écrit :
> > Right, but the calling application has no way to know what the library
> > will accept other than looking at x264_config.h.
> 
> That is not true:
> 
> /* x264_bit_depth:
>  *      Specifies the number of bits per pixel that x264 uses. This is also the
>  *      bit depth that x264 encodes in. If this value is > 8, x264 will read
>  *      two bytes of input data for each pixel sample, and expect the upper
>  *      (16-x264_bit_depth) bits to be zero.
>  *      Note: The flag X264_CSP_HIGH_DEPTH must be used to specify the
>  *      colorspace depth as well. */
> X264_API extern const int x264_bit_depth;

Thanks, I missed these two in the documentation. FWIW, what's the point
of defining them in x264_config.h too then?

> > One example of this is the GStreamer x264 plugin. It has to know
> > beforehand which raw video formats are supported and also what the
> > library will output.
> 
> AFAICS, gstreamer x264 plugin does not worry about bit depth _at all_. That
> is not a good example.

Well, it does nowadays. I'll change it to use the values from the
library instead of the #defines from x264_config.h then.

> > Yes, and as stated above changed the library at runtime is a bad idea
> > because the library will be different from what the application saw
> > during build it x264_config.h.
> 
> If the application is correctly written, it works perfectly (I have done it
> dozens of times) and is very useful. Calling something that works and is
> useful a "bad idea" is a rather unusual use of the expression.

It is a bad idea under the assumptions I had before, and is still a bad
idea without checking first if there is any code in Debian actually
using the values from x264_config.h instead.

It should at least be made more explicit in the documentation that these
two variables (x264_bit_depth and x264_chroma_format) must be checked
and that their equivalents in x264_config.h are completely irrelevant
and must not be used.
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