[FFmpeg-devel] [PATCH] frame: Simplify the video allocation

[Michael Niedermayer]

On Thu, Sep 06, 2018 at 01:10:31PM -0300, James Almer wrote:
> On 9/4/2018 5:09 PM, Michael Niedermayer wrote:
> > On Mon, Sep 03, 2018 at 10:29:13AM -0300, James Almer wrote:
> >> On 9/3/2018 5:17 AM, Michael Niedermayer wrote:
> >>> On Sun, Sep 02, 2018 at 09:34:23PM -0300, James Almer wrote:
> >>>> From: Luca Barbato <lu_zero at gentoo.org>
> >>>>
> >>>> Merged-by: James Almer <jamrial at gmail.com>
> >>>> ---
> >>>> This is the next merge in the queue. It's a critical part of the AVFrame API,
> >>>> so even if FATE passes I'd rather have others look at it and test in case
> >>>> something breaks.
> >>>>
> >>>> The only difference compared to the libav commit is the "32 - 1" padding per
> >>>> plane when allocating the buffer, which was only in our tree.
> >>>
> >>> why is the STRIDE_ALIGN (which is a thing in units of bytes along the
> >>> horizontal axis) added to padded_height which is vertical axis ?
> >>> This is not done prior to the change
> >>
> >> The only way to keep this padding we currently have in the tree applied
> >> to the buffer allocation for each plane like it was before the change
> >> (Except it'll now be one continuous buffer instead of one per plane) is
> >> by passing it alongside the height parameter to
> >> av_image_fill_pointers(). The result is essentially the same.
> >>
> >> Do you want me to change the name of the variable, or remove it and pass
> >> 32 - 1 to both av_image_fill_pointers() calls directly? Removing the
> >> padding will probably just make whatever overreads prompted its addition
> >> to resurface.
> >> Alternatively, i can just no-op this merge and move on.
> > 
> > allocating one plane instead of 3 is better obviously so i dont think this
> > should be no-oped unless someone implements this differently
> > 
> > i dont think the padding can be removed saftely but i might be missing something
> > also i do not remember this 100%
> > 
> > what i see and i may have misunderstood your reply but the code before places
> > a few bytes between planes, the new code places a few lines, that is alot more
> > space. Its not even the best that can be done with the current API. For example
> > the number of extra lines would generally be 1 to provide sufficient padding
> > at most reaslistic resolutions.
> > 
> > also there is the independant question on the API, do we want/need to make 
> > adding padding between planes easier?>
> > actually i think that if we change from 31 bytes to X lines padding then this
> > should be a commit seperate of the 3->1 change. This would make bisect much
> > more meaningfull and its rather trivial to split this.
> 
> Do you have a suggestion on how to choose how many lines of padding to
> add? 

something like (with rounding up)
bytes * horizontal_chroma_subsampling / width * vertical_chroma_subsampling


> And how would it be done? Just passing (h + padding_lines) to
> av_buffer_alloc() pre merge, and to av_image_fill_pointers() post merge?

possible


> 
> It would also be faster if you could commit that change instead.

thinking of this, its maybe simpler to adjust data[*] by these to get
exactly teh same effect as before


thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In a rich man's house there is no place to spit but his face.
-- Diogenes of Sinope
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