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

Paul B Mahol onemda at gmail.com
Wed Dec 7 13:10:38 EET 2022

On Tue, Dec 6, 2022 at 10:56 AM Nicolas Gaullier <nicolas.gaullier at cji.paris>

> >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.
IIRC there was/are some bitstream filters that can change stored flags  at
bitstream level.

> Nicolas
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