[FFmpeg-user] Changing scan type (progressive<->interlaced) without reencoding.

[Steinar Apalnes]

>
> >As the title says, is this at all possible? My concern is mostly with
> mpeg2 and h264 that have content of one type but encoded/marked as another.
> In a general manner, amongst other things, interlaced encoding involves
> interlaced DCT, so this is not possible because it is not a simple "mark".
> In some very limited scenarios, it is possible to tag interlaced content
> as progressive-segmented frame (PsF). Take mpeg2/h264: I have never seen
> any implementation (neither encoder or decoder) of the flags that actually
> allow to mark progressive content, so PsF is pure theory here. So today,
> for example, only "progressive sequence" mpeg2 is considered progressive :
> you have to transcode.
>
> >Most notably content that has progressive video but stored interlaced.
> "encoded" rather than "stored", but yes, it is indeed very commonplace.
> Nevertheless, be very very carefull, it is also very very commonplace to
> have interlaced branding/finishing on progressive content, so it can end up
> with  1 hours of pure progressive content with 3x period of 10s where an
> interlaced title appear or disappear in a corner... This is why
> deinterlacing filters are both so useful and so tricky.
>

I'm all aware of the implications, just need to explore the possibility to
change scan type without re-encoding. Currently it does not seem to be a
"simple" solution to the problem.

-steinar