I thought I'd mention that using ffmpeg and Sage/singular/gfan/tachyon I was able to finish the little pilot project I had in mind: taking a 5d Groebner fan, intersecting it with a hyperplane, rotating it in 4d, and animating the projection into three dimensions. I am still struggling with the options to ffmpeg; I eventually just used "-qmax 2" and nothing else but I am sure that is far from optimal (I did try Vincent's options and it didn't work on OS X, I think I am missing the codex). I think the results are enjoyable:
http://www.d.umn.edu/~mhampton/gf5.mp4 Cheers, Marshall Hampton On Sep 3, 2:52 am, Vincent Beffara <[EMAIL PROTECTED]> wrote: > Hi, > > > Thanks very much for this response. ffmpeg looks very useful to me, I > > am checking it out right now. It is unclear to me what the overlap is > > with mplayer/mencoder. It seems that ffmpeg is somewhat leaner and > > more portable, so I am thinking of using it as the encoder for your > > first suggestion (create a sequence of jpegs > > Rather use a non-destructive compression like tiff or tga, the artifacts > of jpg might become too visible after encoding especially if they vary > from frame to frame. Disk is cheap these days. > > > with the tachyon > > raytracer, then convert to mp4). ffmpeg seems quite fast to me > > compared to using imagemagick with GIFs. > > It should be slower than animated GIFs, but I agree that it is quite > efficient. And quite portable, I even managed to compile it on Solaris > after some tweaking. There are two things to be careful about, and for > which it is quite better than mencoder in my experience: > > - Colorspace encoding : for some reason mencoder wants YCbCr, and > standard packages provide RGB ... Besides, ffmpeg doesn't like 16 bits > per channel, and figuring that one out was tricky (the error message > is a bit cryptic and sounds like "syntax error"); > > - Quality settings for the h264 codec. That is actually the big one. The > main parameter is _not_ the bitrate ! Well, increasing the bitrate > helps, but by default the "hi quality" mode is off and you need some > tweaking. At the time I was experimenting to put bits of Dimensions > online, and it turned out that the following parameters gave a good > result: > > -vcodec libx264 -b $(VBR) -level 30 -mbd 2 -cmp 2 -subcmp 2 -g 300 > -qmin 1 -qmax 31 -flags +loop -chroma 1 -partitions partp8x8+partb8x8 > -flags2 +mixed_refs -me_method 8 -subq 7 -trellis 2 -refs 1 -coder 1 > -me umh -me_range 16 -bf 0 -sc_threshold 40 -keyint_min 25 > > (Yes, that's all a long string of command-line arguments.) For 384x288 > resolution, a VBR of 200 kbps is enough. And I believe you will not > find it so fast :-) > > One last thing: Apple's implementation of h264 is not quite as complete > as the one of x264 (which I find quite ironic), so if you are not > careful the file you produce will not be readable on a mac ... > > I am attaching a Makefile that I used to encode video, in case you find > it useful. Be sure to check out mp4creator after ffmpeg. > > Have fun, > > /vincent > > -- > Vincent Beffara > UMPA - ENS-Lyon > 46 allée d'Italie > 69364 Lyon Cedex 07 > Tél : 04 72 72 85 25 > > Makefile > 1KViewDownload --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
