[Bug 383240] [NEW] Integrate and enable ARMv5TE/v6/VFP and NEON optimisations from ffmpeg trunk for armel

[Reinhard Tartler]

Dave Martin <Dave.Martin at arm.com> writes:

> Public bug reported:
>
> Binary package hint: ffmpeg
>
> Since quite a lot of ARM architecture optimisations are now integrated
> in the ffmpeg trunk, ideally Ubuntu should enable them for Karmic
> onwards.
>
> The related changes have been committed to the ffmpeg trunk at
> svn://svn.ffmpeg.org/ffmpeg/trunk from 2008-08-25 onwards; however, most
> of the support is newer than this.  Some support was present in the
> source used for Jaunty, but it was not enabled (no run-time detection
> was implemented, and the NEON code was statically disabled with
> configure --disable-neon).

feel free to backport these changes to the 0.5 branch of ffmpeg!

> Måns Rullgård (the ffmpeg trunk developer who did the optimisations) is
> concerned that the hwcaps information provided by the kernel to
> userspace is not really sufficient for runtime processor feature
> detection, and is looking at ways of providing more detailed capability
> information to userspace.

checking hwcaps is only necessary at load time, not at link time, since
libavcodec is compiled several times on arm for different targets. This
means that the way the package is built, runtime-cpu detection support
is not necessary.

> However, this support is speculative at present, and is unlikely to be
> merged in all the right places in time for Karmic, so we may need a
> simpler approach, whether it's based on run-time hwcaps checks in
> libavcodec, or using multiple library build passes and the hwcaps-based
> shared library selection in libc, or something else.

The latter approach is already implemented since intrepid. ARM/Neon
support has been introduced by Loïc Minier just in time for jaunty.
Since I don't have experience nor hardware I need to rely on
patches by people who have that expertise.

> ffmpeg also contains some VFP, armv5te and armv6 optimisations. Based
> on the v6+VFP baseline for Karmic, I suggest that these can be turned
> on statically, when the karmic toolchain has stabilised sufficiently.

Feel free to propose further compilation runs and compiler switches, we
can integrate them rather easily. confirm with [1] and feel free to
propose patches to that file.


Fussnoten: 
[1] http://git.debian.org/?p=pkg-multimedia/ffmpeg-debian.git;a=blob;f=debian/confflags
-- 
Gruesse/greetings,
Reinhard Tartler, KeyID 945348A4

-- 
Integrate and enable ARMv5TE/v6/VFP and NEON optimisations from ffmpeg trunk for armel
https://bugs.launchpad.net/bugs/383240
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