On 01/28/2021 04:34 PM, Paul B Mahol wrote:
On Thu, Jan 28, 2021 at 10:23 PM Mark Filipak (ffmpeg) <markfili...@bog.us>
wrote:
Synopsis:
I seek to use minterpolate to take advantage of its superior output. I
present some performance
issues followed by an alternative filter_complex. So, this presentation
necessarily addresses 2
subjects.
Problem:
I'm currently transcoding a 2:43:05 1920x1080, 24FPS progressive video to
60FPS via minterpolate
filter. Apparently, the transcode will take a little more than 3 days.
Hardware:
There are 4 CPU cores (with 2 threads, each) that run at 3.6 GHz. There is
also an NVIDIA GTX 980M
GPU having 1536 CUDA cores with a driver that implements the Optimus,
CUDA-as-coprocessors architecture.
Performance:
During the transcode, ffmpeg is consuming only between 10% & 20% of the
CPU. It appears to be
single-threaded, and it appears to not be using Optimus at all.
Is there a way to coax minterpolate to expand its hardware usage?
Alternative filter_complex:
minterpolate converts 24FPS to 60FPS by interpolating every frame via
motion vectors to produce a 60
picture/second stream in a 60FPS transport. It does a truly amazing job,
but without expanded
hardware usage, it takes too long to do it.
A viable alternative is to 55 telecine the source (which simply duplicates
the n%5!=2 frames) while
interpolating solely the n%5==2 frames. That should take much less time
and would produce a 24
picture/second stream in a 60FPS transport -- totally acceptable.
The problem is that motion vector interpolation requires that minterpolate
be 'split' out and run in
parallel with the main path in the filter_complex so that the interpolated
frames can be plucked out
(n%5==2) and interleaved at the end of the filter_complex. That doesn't
make much sense because it
doesn't decrease processing (or processing time) and, if the fully
motion-interpolated stream is
produced anyway, then output it directly instead of interleaving. What's
needed is an interpolation
alternative to minterpolate.
Alternative Interpolation:
55 telecine with no interpolation or smoothing works well even though the
n%5==2 frames are combed
but decombing is desired. The problem with that is: I can't find a
deinterlace filter that does
pixel interpolation without reintroducing some telecine judder. The issue
involves spacial alignment
of the odd & even lines in the existing filters.
Some existing filters align the decombed lines with the input's top field,
some align the decombed
lines with the input's bottom field. What's desired is a filter that
aligns the decombed lines with
the spacial mean. I suggest that the Sobel might be appropriate for the
decombing (or at least, that
the Sobel can be employed to visualize what's desired).
Sobel of line y: ______/\_____________/\_________ (edges)
Sobel of line y+1: __________/\_____________/\_____
Desired output:
line y: ________/\_____________/\_______ (aligned to mean)
line y+1: ________/\_____________/\_______ (aligned to mean)
I could find this:
line y: ______/\_____________/\_________
line y+1: ______/\_____________/\_________ (aligned to top line
edges)
and I could find this:
line y: __________/\_____________/\_____ (aligned to bottom
line edges)
line y+1: __________/\_____________/\_____
Sorry, but I can not decipher above stuff. Does anybody else can?
I assume you refer to the "Alternative Interpolation" section.
Suppose I explain like this: Take any of the various edge-detecting, deinterlacing filters and, for
each line-pair (y & y+1), align both output lines (y & y+1) to the mean of the input's
line(y).Y-edge & line(y+1).Y-edge. To do that, only single line-pairs are processed (not between
line-pairs), and no motion vector interpolation is needed.
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