[FFmpeg-devel] MXF D10 regression tests

Michael Niedermayer michaelni
Wed Mar 18 21:07:40 CET 2009

On Wed, Mar 18, 2009 at 04:04:49PM +0100, Reimar D?ffinger wrote:
> On Wed, Mar 18, 2009 at 03:40:52PM +0100, Michael Niedermayer wrote:
> > iam not asking for all of it to be taken into account but rather that
> > there is some framework in which such things can be filled in where
> > they are needed.
> > (we also have avcodec_align_dimensions())
> Well, you are the maintainer, I leave it to you to come up with a
> solution. At least it should be clear enough what exactly is the issue
> and can be fixed without access to a PPC machine.
> > currently STRIDE_ALIGN is 8 for x86* and that works out exactly because 420
> > and the linesize relations gurantee 16 byte alignment for luma.
> I want to make completely clear: there is nothing in the code that
> guarantees any "linesize relations", it is pure luck it works, and the
> only reason is that the width is required to be a multiple of 16 and
> STRIDE_ALIGN << chroma_x_shift divides (more precisely is equal to)
> this on x86.
> > if 444 is ever added it will need some special handling like svq1 does,
> > also other archs than x86 set STRIDE_ALIGN to 16 while they possibly
> > like x86 really just mean 16 for luma ...
> Since (probably) none of that is documented that won't be fixed anytime
> soon, at least not by someone who does not know the asm by heart already.

there was a single line of doc until r12178
the code surrounding has changed several times prior

and i simply do not remember which asm or how many if any need this
linesize relation.

it is possible that some of the code expecting the linesize relation was
fixed in the distant past to use uvlinesize/stride

what should be done is
* identify and document which code exactly needs this relation (your patch
  is a start for this)
* find what speed effect it has to fix that code
* depending on the possibility to fix the code without speed regressions
  document which buffers require the relation and fix the code used to
  allocate them
* fix STRIDE_ALIGN for each arch (really a job for the maintainers of that

now if i had more time, no patches to review, no bugs to look into and
there wouldnt be the soon comming soc qual patches ...

maybe you can catch a soc student and convince him to work on that as
qual task?


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

> ... defining _GNU_SOURCE...
For the love of all that is holy, and some that is not, don't do that.
-- Luca & Mans
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