[FFmpeg-devel] RFC: flag rawvideo input as interlaced

[Michael Niedermayer]

On Mon, May 16, 2011 at 11:35:43PM +0100, Mark Himsley wrote:
> On 16/05/2011 20:55, Michael Niedermayer wrote:
> > On Mon, May 16, 2011 at 05:55:13PM +0100, Mark Himsley wrote:
> >> On 16/05/11 15:22, Michael Niedermayer wrote:
> >>> On Mon, May 16, 2011 at 11:45:15AM +0100, Mark Himsley wrote:
> >>>> On 16/05/2011 00:10, Michael Niedermayer wrote:
> >>>>> On Mon, May 16, 2011 at 12:08:24AM +0200, Stefano Sabatini wrote:
> >>>>>> On date Sunday 2011-05-15 19:47:26 +0100, Mark Himsley encoded:
> >> [...]
> >>>>>>
> >>>>>>> If that is a reasonable idea, AVFormatParameters would be the structure
> >>>>>>> to extend.
> >>>>>>
> >>>>>> AVFormatParameters is deprecated and we should get rid of it.
> >>>>
> >>>> Without it, I don't see how ffmpeg.c can pass the width, height, pix_fmt
> >>>> etc etc to raw decoders. There is even a comment that says that
> >>>> AVFormatParameters is "Only used in raw format right now".
> >>>
> >>> there are many options that are passed to the decoders, like for
> >>> example idct type.
> >>>
> >>> Please elaborate on where the problem is
> >>
> >> The problem is my ignorance.
> >>
> >> I want to flag a rawvideo input file as interlaced and of a specific  
> >> field order.
> >>
> >> I therefore think that the appropriate way to do that is to set the  
> >> command line parameter "-top [0|1]" before an input file of format 
> >> rawvideo.
> >>
> >> Therefore I want to get the value of the variable top_field_first from  
> >> ffmpeg.c into demuxer/decoder. As Stefano pointed out, value of  
> >> top_field_first is not used anywhere except for in  
> >> ffmpeg.c:do_video_out(), so putting it into AVFormatParameters to be  
> >> passed to the demuxer/decoder seemed the logical thing to do.
> >>
> >>>>>> Instead,
> >>>>>> we could use demuxers/decoders private options when it makes
> >>>>>> sense. I'm not yet sure where the option should be set (if in the
> >>>>>> demuxer or in the decoder), Michael?
> >>>>>
> >>>>> I dont think theres a single perfect awnser here
> >>>>>
> >>>>> demuxer private options would make it only available for one demuxer
> >>>>> there can be rawvideo in many containers.
> >>>>
> >>>> I have assumed that containers other than rawvideo can flag their
> >>>> streams as interlaced already.
> >>>
> >>> i dont think many can do that currently.
> >>>
> >>>
> >>> also a writing into coded_frame of a decoder from a demuxer is very
> >>> hasckish. there could be no decoder at all or 2 decoders.
> >>> These might be unlikely enough for it to work out in practice but
> >>> its not a pretty way to solve it
> >>
> >> Ok, I understand that. My excuse is that I was just following how  
> >> libavformat/yuv4mpeg.c:yuv4_read_header() and  
> >> libavdevice/v4l2.c:v4l2_read_header() both do it.
> >>
> >> As I said, my ignorance is preventing me from seeing a less 'hackish'  
> >> solution.
> > 
> > Ive implemented it locally, will push in a moment.
> > Please review my changes and comments welcome.
> 
> Thanks Michael. That has explained a lot more about the way ffmpeg works
> too.
> 
> I have one concern, given this psudo command:
> 
> ffmpeg -top 1 -i input -vf fieldorder=bff -vcodec dvvideo -flags +ilme
> output
> 
> ffmpeg.c:do_video_out() will be setting big_picture.top_field_first to
> 1, where as the fieldorder filter has converted the tff input file to
> bff. That was why I was resetting ffmpeg.c:top_field_first to -1 in
> ffmpeg.c:opt_input_file.

indeed, ive added the reset back to opt_input_file() locally will push
soon

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

I do not agree with what you have to say, but I'll defend to the death your
right to say it. -- Voltaire
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