[FFmpeg-user] bwdif filter question

[Carl Eugen Hoyos]

Am So., 20. Sept. 2020 um 06:59 Uhr schrieb Mark Filipak (ffmpeg)
<markfilipak at bog.us>:
>
> On 09/18/2020 03:01 PM, Carl Eugen Hoyos wrote:
> >> Am 16.09.2020 um 15:58 schrieb Mark Himsley <mark.himsley at gmail.com>:
> >>> On Mon, 14 Sep 2020 at 15:42, Mark Filipak (ffmpeg) <markfilipak at bog.us> wrote:
> >>> Is the input to the bwdif filter fields or frames?
> >> The input to every filter in a filter chain is a raster of pixels.
> >> That raster may contain one frame or two fields.
> >
> > That may not be wrong (apart from Paul’s comment) but I wonder how useful it is:
> > No matter if the raster contains one field, two interlaced fields or a progressive
> > frame, the filter will always see an input frame.
>
> "...if the raster contains *one field*...the filter will always see an input *frame*."
> How is that possible? How can a frame contain just one field?

The following makes little sense, it is just meant as an example:
$ ffmpeg -f lavfi -i testsrc2,field -vf bwdif -f null -

Here, the input to the bwdif consists of frames that contain one field
(of the original input).

> > The fact that there is metadata that may signal the content is also not necessarily
> > helpful as this metadata is typically wrong (often signalling fields when a frame is provided).
>
> Can you provide an example (or a link to an example)? I've examined a
> great number of DSM mpeg presentation streams ('VOB's & 'm2ts's) and
> I've not seen a single case. What metadata are you looking at?
> sequence_extension: 'progressive_sequence'?
> picture_coding_extension: 'picture_structure'?
> picture_coding_extension: 'top_field_first'?
> picture_coding_extension: 'repeat_first_field'?

I would expect that most commercial encodings you have uses
one of the above, independently of the content...

> picture_coding_extension: 'progressive_frame'?

... while this is unusual, even for movies in PAL streams.

Otoh, I typically saw pal dvb streams, maybe my claim is
only true for them.

Carl Eugen