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Old 23rd October 2004, 17:36   #1  |  Link
Tommy Carrot
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Snow wavelet codec

I think Snow codec has reached the point where it should deserve an own thread here. :) If someone wouldn't know what Snow is, it's an experimental wavelet codec made by the ffmpeg developers, and despite the "experimental" label, it's probably the most mature wavelet codec out there with very good performance, far surpassing other wavelet codecs (rududu, dirac) and imho mpeg4 ASP codecs (xvid, divx etc.) too, quality-wise. As it's part of the libavcodec codec library, there are several applications with Snow support, like ffmpeg, mplayer/mencoder and of course ffdshow.

Snow has a few settings which are probably not obvious at first glance, let's see them in mencoder, here is a command line example with the more important options:

mencoder in.avi -o out.avi -ovc lavc -lavcopts vcodec=snow:vstrict=-2:vqscale=3:pred=0:cmp=1:subcmp=1:mbcmp=1:qpel

Detailed descriptions of the various options are here.

Note: vqscale specifies the encoding quality, basicly it's the quantizer. If you leave it out from the command-line, snow will compress losslessly (lossless mode doesn't work with pred=0 currently!). 2-pass mode is also available, but in my experience it's far from perfect yet, it doesn't really hit the required bitrate, and it gives significantly worse quality than constant quantizer mode at comparable bitrate.

Recommended settings: I'd strongly suggest to set all cmp functions to 1 (sum of squared errors method) for minimalising the chroma (and other) artifacts. Enabling qpel is also recommended for better detail preservation. Theoretically using smaller motion partitions (:v4mv) should further improve the compression efficiency, but due to the immature state of snow, it has side effects (artifacts, less accurate ME etc), so i cannot recommend it yet.

Outside mencoder, FFdshow can also be used for encoding Snow, it's more user-friendly, but apparently not everything is right with the snow encoder implementation in it, because the output quality is inferior to mencoder (ffdshow adds a slight vibration to the video, the motions are not smooth, the finer details are jumping around... i can't explain it better, but the effect is obvious during playback. Enabling 4 mv option makes this phenomenon even worse.)

BTW, don't use Snow for archiving, experimental means that the bitstream might change during the development, so it's not guaranteed that current encodings will be decodeable with the future versions.

Last edited by Tommy Carrot; 6th January 2006 at 02:27. Reason: updating vstrict to -2
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Old 23rd October 2004, 18:03   #2  |  Link
virus
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Quote:
Originally posted by Tommy Carrot
...but i think the next ffdshow will include it...
oh, that's good. hate 6-lines-long commandlines

BTW maybe your post can be split to a "snow development" thread?
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Old 23rd October 2004, 18:19   #3  |  Link
Tommy Carrot
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Quote:
Originally posted by virus
BTW maybe your post can be split to a "snow development" thread?
Probably starting a new thread would've been a better idea, but oh well.

Anyway, here is a test encoding, as the name says, the bitrate is 288 kbit/s, just to have some ideas what this codec is capable of.

Right now only mplayer can play it back, hopefully the next ffdshow build is coming soon.
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Old 23rd October 2004, 19:40   #4  |  Link
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Best settings in my test are unanimously qpel:pred=1:mbcmp=1, but with animated and DV source. Not sure if live action DVD source would be different. CMP functions may not be accurate on my side because I don't have SSE, though encoding with them worked and did show differences.
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Old 23rd October 2004, 19:49   #5  |  Link
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This SSE is not the refer to the instruction set, but another method for the ME. It's more accurate, but slower.

Pred=1 indeed benefits the quality, but it makes the playback so much slower that i cannot play back the video in realtime.

What is your opinion about :v4mv? IMO it increases the sharpness and the detail level at higher bitrates, so that's a good feature too.
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Old 23rd October 2004, 20:03   #6  |  Link
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Ah yeah, duh, sse as in sum of squared error. I was still in the cpu mindset ~_~
My results only reflect size loss in the lossless mode, I'm in the process of testing lossy atm.
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Old 23rd October 2004, 20:46   #7  |  Link
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Quote:
Anyway, here is a test encoding, as the name says, the bitrate is 288 kbit/s, just to have some ideas what this codec is capable of.
Man, this is unbelievable !
This project seems to continue where Ogg Tarkin has left...
Are there any developers from the former Tarkin project active on SNOW ?
I also hope that'll be included with next ffdshow version.

cheers

P.S.: Wasn't the project goal of Tarkin to fit a whole movie on a zip disk ?

Last edited by Rrrough; 23rd October 2004 at 20:49.
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Old 23rd October 2004, 21:18   #8  |  Link
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now THOSE are awsome results!
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Old 23rd October 2004, 21:49   #9  |  Link
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Pred=1 gives a nice quality boost and is still playable in realtime here, whereas lossless encoding doesn't playback in realtime (2 min 640x272 => 180 MB )
Pred=2 is really too CPU hungry for realtime playback, but quality is definetly nice !

Last edited by Rrrough; 23rd October 2004 at 23:10.
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Old 23rd October 2004, 22:01   #10  |  Link
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Great job with introducing us to snow Tommy Carrot,
the codec is simply STATE OF THE ART!
I made some tests with a quantizer of 6 and I cant believe how great the output is.
Not sure yet but v4mv does provide a more detailed picture but introduces some artifacts like ringing around objects,and maybe stronger colour mismatches. So at this quantizer I prefer to avoid it.
I have a videoclip from a sattelite source that is very difficult to compress, and snow managed to give an excellent picture at 480 Kbps!!!!!! Previously I would have to go as high as 600kbps to get a "watchable" picture . (264 codecs are not taken in to account, I am sure it will do well with atemes codec as well).
And with one pass. Imagine it being more mature and having a two pass option!!!! It will easilly surpass all other (current) codecs!!!!
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Old 24th October 2004, 03:22   #11  |  Link
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Err... I got the Sample of the Snow-Codec and had found out the codec is also readable by VLC 0.80 ... by the way
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Old 24th October 2004, 05:45   #12  |  Link
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Be careful of trying to play Snow with any stable release. It changes often, and isn't always backwards compatible, sometimes in subtle ways.
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Old 24th October 2004, 13:23   #13  |  Link
Tommy Carrot
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Quote:
Originally posted by akupenguin
Be careful of trying to play Snow with any stable release. It changes often, and isn't always backwards compatible, sometimes in subtle ways.
I'm aware of this, snow has no practical value right now, but still, i think it's a very interesting codec.

Btw, sorry guys, i was wrong, pred=1 doesn't make the decoding slower, i confused it with pred=2, and yes, it gives a nice quality boost, so it's good to have activated imo.

I've made some quality comparison against xvid with the following settings:
xvid - mpeg quantizer, vhq4, qpel, gmc, b-frames
snow - qpel, v4mv, all cmp function = 1, pred=1

and in every occasion snow is the clear winner, it gives more detailed image and no artifacts, so i would say snow is already better than xvid in almost every case.
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Old 24th October 2004, 13:55   #14  |  Link
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hi,

it sounds good. where can we get this codec to test it?


thank you


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Old 24th October 2004, 14:07   #15  |  Link
Leak
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Quote:
Originally posted by DeepDVD
Err... I got the Sample of the Snow-Codec and had found out the codec is also readable by VLC 0.80 ... by the way
Well, it tries at least - for me, it freezes after 15-20 seconds and crashes a few seconds later...

Still, what I can see before the crash looks really promising.

np: Autechre - Squeller (EP7)
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Old 24th October 2004, 17:58   #16  |  Link
gldblade
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Wow. That was by far the most impressive encode I have ever seen. Only 3 megs? Wow.

@wunschkind
At the moment the codec only exists in the mplayer/mencoder package that everyone keeps linking to. Unfortunately its command-line only. It also doesn't support Avisynth files (you can encode directly from vob files though, the disadvantage is no filters). See Tommy Carrot's post for information on how to encode. In order to play the encoded video files, use mplayer movie.avi -vo directx.

Last edited by gldblade; 24th October 2004 at 18:06.
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Old 24th October 2004, 18:24   #17  |  Link
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@gldblade
Quote:
I want to test encode using some vobs I have lying around, how would I do it?
as akupenguin's method of piping AVS to mencoder via AVS2YUV (see x264 development thread) doesn't work for me on windows (haven't tried with linux yet) I'm encoding a reasonable amount of frames with huffyuv or ffv1 and transcode the resulting avi with mencoder using snow.
If anyone knows an easier method, please let me know.

Last edited by Rrrough; 24th October 2004 at 18:37.
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Old 24th October 2004, 18:36   #18  |  Link
gldblade
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@Rrrough
Haha, right after making my post I discovered that I can encode directly from vob files since apparently the package can decode mpeg2. Unfortunately there is then no resizing, cropping, and filter. Still good enough for testing purposes, although I'm open to other suggestions.
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Old 24th October 2004, 18:40   #19  |  Link
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Yeah, encoding directly from VOB's would be easier with the problem of missing filters. Are you sure though that cropping and resizing doesn't work ? Gonna try...
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Old 24th October 2004, 18:45   #20  |  Link
gldblade
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Actually I'm not familiar with mplayer/mencoder. Does it support video manipulation of any kind?

*EDIT*
It does apparently, which makes mencoder much more useful. The following page details how, along with other potentially useful information. http://www.mplayerhq.hu/DOCS/HTML/en...dvd-mpeg4-crop

Last edited by gldblade; 24th October 2004 at 18:50.
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