formats and archiving

[Brian MacWhinney]

Dear Info-CHILDES,

     A few further comments on the issue of audio/video formats and  
the importance of archiving.

1.  Thanks to Devin Casenhiser for pointing out a  possible method  
for extracting video from the DVD format.  Of course, this method  
only applies to home-made DVDs.  If someone could get it to work with  
commercial DVDs they would surely get rich (perhaps illegally?).   
Even within the framework of extracting video from homemade DVDs,  
however, I noted some limitations.  For example, you purchase and  
install a recent QuickTimeMPEG2 decoder.  However, even with this  
decoder installed, I found that I was only able to play back the  
first 11 second of a 20-minute video clip.  If you can create content  
using some DVD format and then are able to pull out the content using  
QuickTime, then that is fine.  However, personally, I would not rely  
on this process until I had shown it to work fully using some  
specific hardware/software platform.  In any case, I would not rely  
on the MPEG-2 on the DVD as a replacement for mini-DV as the long- 
term archive.

2.  I had not thought about the issues with mini-DV archiving and  
tape mould in tropical climates that Madalena Cruz-Ferreira  
mentioned.  In this case, I would recommend shipping your mini-DV  
tapes to a colleague in a northern climate for storage.

3.  For the current CHILDES and TalkBank collections, I have relied  
for awhile on DVD-ROMs for keeping copies of the compressed video and  
the original audio.  The major problem I have noted with DVD-ROM  
storage is that it is very easy to scratch the media.  Once this  
happens, the whole disk is unreadable.  So, this is a sort of  
catastrophic failure.  The rate of this type of failure is not large,  
but it is high enough that I have come to rely on both hard disk and  
DVD-ROM as storage for compressed video and WAV audio.

4.  I double-checked with Peyton Todd to make sure I understood the  
thrust of his message.  His central point was that it makes no sense  
to archive digital raw video (AVI format on Windows) because it is  
simply too big.  I agree and that is why I emphasize archiving based  
on mini-DV.  However Peyton was worried about the longevity of mini- 
DV, pointing to problems he had experienced with half-inch reel-to- 
reel tapes.  I think Peyton is talking about the consumer level reel- 
to-reel video of the 1970s and early 1980s.  It is true that this  
format has caused us some problems, but I am not convinced that the  
problem is with the tape medium, but rather with the flakiness of the  
slowly degenerating playback heads on the machines we have to use to  
read these old videos.  By comparison, I have had zero problems  
playing back reel-to-reel audio tapes from up to 35 years ago that  
colleagues have sent us.  Peyton's third point was that archiving of  
the original is not enough when you also do extensive editing with  
the compressed files.  I totally agree with that too.  Most of the  
material in CHILDES and TalkBank is not edited, except to throw out  
dead spaces at the beginning and end of tapes.

5.  A further note on MPEG formats.   MPEG-1 and MPEG-2 videos  
created on Windows (but not Mac) often have the sound track MUX-ed.   
When this is done, it becomes impossible to edit the material in  
QuickTime.  Perhaps some future version of QuickTime will solve this  
problem.  Moreover, many more recent versions of MPEG-1 and MPEG-2  
compression on Windows no longer using MUX-ing, so this problem may  
also go away.  However, if you use MPEG,  it is a good idea to check  
your video inside QuickTime (Movie Properties) to make sure it is not  
using MUX.  MUX is an abbreviation for multiplexing and it involves  
some sort of interlacing of the video and audio that makes subsequent  
analytic processing difficult or impossible.

6.  Finally, let me pass on a comment regarding Carolyn Chaney's  
problems trying to get her techie undergrads to understand the  
usefulness of the playback functions in the old cassette recorders.   
I can only agree.  It was so nice to be able to push a button and  
rehear a sentence.  Of course, we have this type of function inside  
CLAN now in the SoundWalker mode, but all this requires you to be at  
your computer and it was so nice to have a little cassette player you  
could just put in your pocket and still be able to rewind.  Maybe  
some genius will be able to figure out a method for simulating this  
on an iPod some day.

Thanks for all your comments.  And happy recording, compressing, and  
archiving.

--Brian MacWhinney