On Fri, 7 Apr 2006, Nicolas wrote:
> Huh? It's written in the manpage of mplex:
> -V|--vbr
> Set variable bit rate multiplexing. This is needed to multiplex
> variable bit-rate video streams correctly.
Right - but '-f 8' implies VBR ;)
> I don't apply any filter. I spent 2 evenings trying to find good
Ok - that's the cause (at least indirectly) of the problems. The
encoder's spending too many bits on preserving noise :(
> settings to denoise the video without any success. Each time the result
> was blur. There was far less details on the pictures...
> There's a lot of camera shake, and the video comes from an analog
I know that will drive up the bitrate.
> camcorder. It's noisy indeed, and some scenes are shot in a forrest (lot
> of details in the background). The edges are blacken using yuvscaler.
Ah, good - the junk in the edges (especially the bottom) will waste
a lot of bits. 'y4mshift -b' can also be used to blacken the borders.
y4mshift can also center (using -n and -N) the image within the frame
(useful if the black borders are much larger on one side than the
other side).
> In fact, I'm archiving old Hi8 cassettes shot around 10 years ago.
Using a MJPEG (is this the DC30+ that's been mentioned or have I
confused this thread with a different one) card?
> > There's something about the source that's creating files that
> > are right on the edge of being usable.
>
> You probably guess right... The video is really noisy. But I really did
> not find any correct solution to remove the noise without softening very
> much the video. The last thing I tried was that :
Several things that might help:
1. A mild lowpass filter. Yes, y4mspatialfilter can soften the image
if the parameters are too low but a MILD application of a spatial
filter can reduce the noise without losing too much detail
y4mspatialfilter -L 5,0.92,5,0.92
will only reduce the luma bandwidth 8% - could remove a lot some
noise but not a lot of detail.
2. Filter only the chroma. Chroma coming from old analog tapes is
quite dirty from what I've seen can be aggressively filtered.
> 0 -I ACTIVE_702x560+8+8 -M BICUBIC | yuvdenoise -s 2,6,6 -g 0,0,0 -t
> 4,5,5 | /usr/bin/yuvmedianfilter -t 0 | /usr/bin/y4munsharp -L 1.0,0.2,0
One thing that you will notice, if you do upgrade to the cvs version
is that 'yuvdenoise' no longer has the -s and -g options. Those
options offered a lot of flexibility that I miss now.
While you still have the old yuvdenoise you might try the milder
settings of "-s 1,2,2 -g 0,0,0 -t 2,4,4". That should lose almost
no detail but still remove a lot of the noise.
3. heavy center pixel weighting median filter. Maybe something like
"yuvmedianfilter -f -R 1 -r 1 -w 16" will be effective.
But I would avoid 'y4munsharp' if the source is noisy.
y4munsharp sharpens the NOISE which makes it look even worse and raises
the bitrate needed even more :(
4. y4mdenoise is slow but effective. Have you tried that filter?
> > Maybe adding -E to the encoding parameters will help lower the peak rate.
>
> I fear that could reduce the video quality. It really need to be
Ah, so you haven't tried it ;) It's not a "filter" in the same
way as you might be thinking ("yuvdenoise").
There are some items that the eye can not see but the encoder will
spend a lot of bits on because they're very hard to encode. -E
can help the encoder save bits in certain cases (it's not a constant
"filter" like yuvdenoise!).
I think a new slogan is needed: "invisible quality is wasted bits" :)
But if you're that serious about having these precious videos being
playable 20 years from now I'm surprised you haven't invested in
some higher-end capture equipment and software... ;) There are some
fantastic plugins available for FinalCutPro that could be quite useful.
The other thing I 've noticed when processing (old) analog tapes is
that they deteriorate over time - almost every single one I've looked at
(with the software scopes) has had a color cast problem. Color
correction and black level adjustment can do wonders for a video (a
slight lowering of the black level, also known as "crushing the
blacks", can improve the perceived contrast and richness of the
video). Then too desaturating the lows (dark) can improve the
appearance and lower the bitrate (slightly).
Good Luck with your latest encoding run.
Cheers,
Steven Schultz
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