Using ffmpeg to divide a video into many clips.

Although this seems ludicrously obvious now, a few months ago I was completely unable to come up with a good solution for automatically separating one video into many different clips. After a while I finally stumbled on something suggesting ffmpeg as a solution. And come to find out it's actually relatively easy:

ffmpeg -ss xx.xxx -t xx.xxx -i /foo/bar.in.mpg -sameq /foo/bar.out.mpg

In order to then automate this I wrote a short python script that also used rpy2 to grab data on what times I needed video from out of my data in R. Then I just used something like the following to extract 1.6 seconds around each point of time in the list times that I had grabbed from R

for time in times:

    filename = '/foo/bar.in.mpg'

    dur = "00:00:01.600"

    secs = str(datetime.timedelta(milliseconds=(time-800)))

    cmd = ''.join(['ffmpeg -ss ',secs,' -t ',dur,' -i ',filename,' -sameq ','/foo/bar.out.mpg'])

    os.system(cmd) 

I've seen other places suggest to use the -vcodec copy -acodec copy options, however this made the clip begin not where I had specified after -ss, but rather at the closest key frame. Using -sameq does take longer and is lossy because the clip is reencoded, but it starts the clip exactly where you specify it. 

Although I used python and R, this could have been accomplished entirely within R, or with any other data source and scripting language. Something similar can be done to extract still images. The ffmpeg documentation is a great resource.

Local type with MacTeX 2010 (TeX Live 2010 as well?)

I just upgraded to MacTeX 2010 and had some trouble with previously installed type files in my private tree. Using MacTeX 2009 everything was installed appropriately in my local tree (~/Library/texmf) as well as the privately generated ~/.texlive2009 (cf the TeX Live 2010 documentation). I thought all I would need to do is rename the second directory to ~/.texlive2010, and keep the texmf in the library the same. This, however didn't work. 


I took the long way and reinstalled Minion Pro (easy with my script) as well as a few other local fonts. (With a detour through subversion hell: move, recursively delete .svn files, revert to old version, move back, commit) This then generated a new folder: ~/Library/texlive/2010 which seems to be the new home for privately generated files (although this doesn't seem to be documented for either the TeX Live or MacTeX). 


On further investigation it seems that the ~/Library/texlive/2010 directory is now where map files as well as local font files go:


kpsewhich pdftex.map returned ~/Library/texlive/2010/texmf-var/fonts/map/pdftex/updmap/pdftex.map


Almost all of this digging was done very cursorily, but since I didn't see any documentation (other than some for MkIV ConTeXt) I wanted to get this out here. What's not clear is if .texlive2010 has any purpose for MacTeX 2010.