[FFmpeg-user] bwdif filter question

Mark Filipak (ffmpeg) markfilipak at bog.us
Sun Sep 20 07:55:47 EEST 2020

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 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'?
picture_coding_extension: 'progressive_frame'?

> That’s why the filter ignores the information by default.
> (If you provide only one field, no FFmpeg deinterlacer will produce useful output.)
>> The bwdif filter will interpret a single raster and is designed to
>> output two rasters, each containing one or the other of the fields
>> that were contained in the input raster.

"...interpret a *single raster*...one or the other of the fields...in the *input raster*."
Mark Himsley, how are you defining "raster"? I thought you were equating a "single raster" with a 
frame and "two rasters" with fields, but now I'm unsure what you mean.

> You can request that the filter outputs one instead of two rasters for one input raster.

COVID-19 perspective, 0 AM UTC, 20 September 2020.
Yesterday, China: 14 new cases, S.Korea: 110, U.S.: 42,533.
Today, U.S.: 4% of world population, 22% of cases, 21% of deaths.
Today, U.S.: Of 4,427,517 resolved cases, 95% lived, 5% died.
22 Jan: U.S. & S.Korea reported 1st cases on the same day.
6 Mar, S.Korea: 140,000 total tests; results in 4 hours.
6 Mar, U.S.: 2000 total tests; results in 1 to 2 weeks.
May, for the first time, U.S. care-homes are required to report.
1 Jun, total care-home deaths, S.Korea: 0, U.S.: 26,000 to 40,000.
5 Aug, U.S. tests still only 1/4 of number needed; 4 day results.
1 Sep, over 60% of U.S. nurses still lack protective equipment.
18 Sep, U.S. doctors & nurses still acutely lack PPE; 1200 dead.

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