On 09/20/2020 05:44 PM, Carl Eugen Hoyos wrote:
Am So., 20. Sept. 2020 um 06:59 Uhr schrieb Mark Filipak (ffmpeg)
<markfili...@bog.us>:
On 09/18/2020 03:01 PM, Carl Eugen Hoyos wrote:
Am 16.09.2020 um 15:58 schrieb Mark Himsley <mark.hims...@gmail.com>:
On Mon, 14 Sep 2020 at 15:42, Mark Filipak (ffmpeg) <markfili...@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).
Thanks, Carl Eugen. Kindly forgive my ignorance -- I can't read 'C' code and probably couldn't find
the relevant code section if my life depended on it.
If bwdif is the *only* filter, then, from previous discussions, I understand that its input (i.e.
the decoder's output) is raw frames (e.g. 720x576)? If raw frames, then I can understand the above
to mean that the filter is 'fed' only one field (e.g. 720x288). Logically, to me, that would be a
frame (i.e. a 720x288 frame), but no matter (let's forget that). However, even then, the filter is
receiving only one field. How can it 'deinterlace' a single field? I'm mystified. Does it line
double in such a circumstance? Or does it deinterlace the current single field with the next single
field one frame later?
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...
Based on my experience, and to the best of my knowledge, every MPEG PS & TS have all 5 metadata
values. Certainly, every MPEG stream *I've* parsed have all 5.
picture_coding_extension: 'progressive_frame'?
... while this is unusual, even for movies in PAL streams.
For what it's worth, I have only one PAL movie, "The Man Who Would Be King", from Australia. It has
all 5 metadata values and appears to be a regular MPEG PS.
Regarding 'progressive_frame', ffmpeg has 'interlaced_frame' in lieu of 'progressive_frame'. I think
that 'interlaced_frame' = !'progressive_frame' but I'm not sure. Confirming it as a fact is a side
project that I work on only occasionally. H.242 defines "interlace" as solely the condition of PAL &
NTSC scan-fields (i.e. field period == (1/2)(1/FPS)), but I don't want to pursue that further
because I don't want to be perceived as a troll. :-)
- Mark.
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