[FFmpeg-devel] [PATCH 0/7] Container level frame cropping parameters

[Anton Khirnov]

Quoting James Almer (2023-10-10 13:58:00)
> On 10/10/2023 8:54 AM, Anton Khirnov wrote:
> > Quoting James Almer (2023-10-10 13:44:19)
> >> On 10/10/2023 8:17 AM, Anton Khirnov wrote:
> >>> Quoting James Almer (2023-10-07 18:24:56)
> >>>> This is a simple set to add support to stream wide, container level cropping
> >>>> parameters, as featured in formats like Matroska and ISOBMFF. It's needed for
> >>>> things like AV1 streams generated by certain hardware encoders that produce
> >>>> dimension aligned output, and unlike H26x, can't export cropping info within
> >>>> the bitstream.
> >>>> In this set i add the packet side data type, mux and demux support to Matroska,
> >>>> and handling code to ffmpeg and ffplay. Missing is support for clap boxes in
> >>>> ISOBMFF, and exporting the relevant side data from encoders like AMF.
> >>>>
> >>>> It's a rebased and updated version to the set i sent a month ago.
> >>>
> >>> Why is there no lavc-decoder handling? I would expect cropping side data
> >>> submitted to lavc to be somehow propagated to decoded frames.
> >>> Though there is a question of how to combine side data with the
> >>> codec-level cropping.
> >>
> >> I thought about adding lavc support alongside the CLI handling, yeah.
> >> And it should be a matter of adding the values to the existing ones in
> >> frame->crop_* as exported by decoders, which av_frame_apply_cropping()
> >> will then handle.
> >>
> >> And the reason i add support to the CLI by including a filter instead of
> >> leaving it up to lavc is that av_frame_apply_cropping() may not do exact
> >> cropping if AV_CODEC_FLAG_UNALIGNED is not set.
> > 
> > I intend to have the CLI always set AVCodecContext.apply_cropping=0 and
> > have it handled by lavfi for this exact reason, just didn't get to
> > actually doing it yet. Feel free and welcome to do it yourself.
> 
> The cropping filter doesn't look at the frame cropping fields, though. 
> It in fact exports cropping into them if you pass it hw frames. It only 
> looks at input arguments. So it doesn't seem like that can be done 
> without changing the filter.

I mean ffmpeg CLI would look at the frame cropping fields and insert the
crop filter accordingly, as it does for other bits of metadata.

-- 
Anton Khirnov