[FFmpeg-devel] [PATCH] Add coded_width/height to AVCodecParameters

[Michael Niedermayer]

On Sun, Apr 03, 2016 at 03:31:59PM +0200, wm4 wrote:
> On Sun, 3 Apr 2016 15:26:02 +0200
> Michael Niedermayer <michael at niedermayer.cc> wrote:
> 
> > On Sun, Apr 03, 2016 at 02:31:06PM +0200, Hendrik Leppkes wrote:
> > > On Sun, Apr 3, 2016 at 2:07 PM, Michael Niedermayer
> > > <michael at niedermayer.cc> wrote:  
> > > > Without this or some other change moving data back and forth corrupts it
> > > > as the cropped & possibly low res resolution modified w/h will be taken
> > > > a the pre lowres resolution
> > > > also without 2 sets theres no place to communicate the cropped dimensions
> > > >
> > > > can be reproduced with
> > > > ./ffplay_g -vlowres 2 tickets/162/avid.avi
> > > >  
> > > 
> > > lowres is supposed to be applied in the decoder, not the demuxer, so I
> > > don't see how this is required here.  
> > 
> > if iam not mistaken (please correct me if iam wrong)
> > 
> > the demuxer runs a decoder, which initializes various AVCodecContext
> > fields these then get copied into AVCodecParameters and back into
> > the users AVCodecContext used for the user appliations decoder
> > 
> > the first decoder will set width & height to the low resolution
> > with lowres, coded_width / height will represent the stored, true
> > width/height
> > the data copied into the AVCodecParameters will have lost the width
> > & height that is stored anywhere but rather contain the lowres
> > variant.
> > 
> > the user app then will initialize its decoder based on coded_width
> > and coded_height which it will find set to 0 so it fallback to the
> > compatibility hack of using width & height which are the lowres
> > values and the decoder will apply the lowres stuff again
> > 
> > above is based on some assumtations i have not verified very step with
> > a debugger
> > 
> > 
> > > AVCodecParameters is supposed to contain container information, not
> > > pre-interpreted info based on some decoding options.  
> > 
> 
> This just shows how broken using decoders in libavformat is by design.
> The output parameters of a decoder have not necessarily anything to do
> with the input codec parameters.
> 

> In any case, not sure why we'd care about an obscure semi-broken
> feature like lowres anyway.

what is broken on lowres in ffmpeg git master ?

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Modern terrorism, a quick summary: Need oil, start war with country that
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and strip your own citizens of their rights and freedoms. to be continued
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