On Tue, 16 Dec 2003, Slepp Lukwai wrote:
> Tried it without any options, same effect. I'm definitely seeing nowhere
> near 40% speedup, which is what boggles me. I expected at least
> reasonable gains of 25%.
I think that has to do with the -I setting...
> Sorry, upon further testing, I actually average around 14fps at DVD
> quality (720x480, 9800kbit/s). (see all the details of my command lines
Ah, that's more like it then.
> It's interesting that I'm faster with dual 2100s than the dual 2800 (or
> at least on par). I suppose it really comes down to command line
> options, but you would need to compare those yourself (since I haven't
Friend of mine has dual 2400s and my setup is ~10-15% faster as I
recall - he's getting around 11fps as a rule where I see 14 or so.
I'm usually adding a bit of overhead with the chroma conversion. I
build smilutils with ffmpeg/libavcodec (to use ffmpeg's DV codec)
and then run the data thru something like:
"smil2yuv -i 2 file.dv | filters | y4mscaler -O chromass=420_MPEG2 |..."
Produces better output that the default which uses libdv but does
cost a bit in cpu use.
> According to the docs -I 1 turns on interlacing support, and causes
> un-needed overhead if it is known progressive material. Hence the -I 0
> (plus transcode sets that, though I could override it).
But unless you have the raw 23.976fps progressive data (with the 3:2
pulldown undone) then I think '-I 1' is the option to use. But then
I might be confused (wouldn't be the first time ;)).
That would explain why the encoding rate I see is lower since I'm
using -I 1.
> > wrong I'm sure someone will tactfully point that out ;)) the speedup
> > comes from the motion estimation of the 2 fields/frame being done in
> > parallel.
>
> Oh. Son of a... If that's all it is...
Yep - I'm fairly sure that is why you're not seeing any improvement
when using "-M 2".
> > without B frames. Those are computationally a lot more expensive
> > than I or P frames. "-R 0" will disable B frames.
>
> I just enabled that, and that's how I'm hitting 15fps instead of 8, and
> the quality is good and the size is just fine.
Great! It takes, from what I've seen, extraordinarily clean sources
before -R 0 has no or little effect.
> to their potentials and give me the equivalent of a 4200+ ;> If it takes
> 6 hours to transcode a movie because I set -r32 (I noticed a larger
> difference with -4 -2 options, btw, than -r16 vs -r32), that's fine, but
Yep - "-4 1" will close to double the time over "-4 2" and the
difference in bitrate/filesize is measured in tenths of a percent.
Hardly worth it. Not all that much difference between "-4 2" and
"-4 3" though.
> > better results (especially with clean source material) can be obtained
> > with "-E -8" or perhaps "-E -10".
>
> Until I upgraded to .92, I didn't have those options. I'm using them
On noisy source material the -E option has almost no effect but the
cleaner the input the more effect even modest values of -E have.
> now, in combination with -Q, but I find the artifacts are almost never
> there (I used to do -q 4 and -Q 4.0, and it looked about the same as the
> 5/3.0).
Perhaps Richard Ellis could chime in with his experiences with -Q ;)
> > Right, with -I 0 the cpus take turns but there's little parallelism.
>
> And again, son of.... I didn't realize the parallelization was done
> based on interlacing settings.
Looking back on it that makes sense though. A P frame depends on the
preceeding P frame - rather sequential in nature since you can't
move on to the next one without completing the first one...
> The MPEG decoding doesn't take much, and the pipe overhead is negligble,
Pipe overhead sneaks up on you though. One pipe? Not a real problem,
two? Begins to be noticed but isn't too bad. Four or five? Yeah,
it starts to take a hit on the overall speed of the system - the data
has to go up/down thru the kernel all those times and that's not "free".
> (As I write this, I'm still waiting for the -M 2 run to finish, so it'll
> arrive before the tests results to Bernhard make it out).
You might try, for timing purposes, without -I 0 and see what, if any
effect that has. Might be a useful data point.
Cheers,
Steven Schultz
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