Digitizing web videotapes for web distributions.
- Digitize your movie using mediarecorder, following
the instructions on the capture tutorial.
- Split longer videos into into several logical segments of
roughly 30 seconds or a minute. (If you just split them on the one
minute mark, then they'll break right in the middle of a sentence
which is disconcerting. So try to have the segments be aligned with
- Use the realtime SGI hardware-dependent compression at this
stage. The segment boundaries can be very rough, you'll deal with
frame-accurate trimming in the next stage.
- Import each clip in turn into Premiere, and use its trim
capabilities to set exact boundaries. See the Premiere tutorial for pointers.
Use QuickTime Composite output, not QuickTime Movie output.
- Recompress each video segment with device-independent
compression using the command-line dmconvert
interface. It's much faster to crunch it this way instead of
- The right place to put your resulting videos is
/n/graphics/web/content/docs/videos/. Make yourself a
directory to put all the pieces in, and make an index page so that
people can download the components separately. It's useful to list
both the time and size of each segment. Add pointers to your directory
from the main index page if you want the video
to be publicly accessible. If your video has an accompanying paper,
consider creating crosslinks between the paper page and the video
page. Consider also grabbing screenshots of the first frame of each
segment as a visual directory, as in this example.
(Note that there is a separate page
for creating a web version of a video directly from Premiere.)
Recommended first stage digitzing settings
Size: Use 320x240 (halfsize) frames. Fullsize 640x480 results in files too
big to download.
- Compression: use hardware JPEG.
Recommended second stage trimming settings
- Output video: Key difference from main Premiere tutorial
directions is that you want to create output that is QuickTime
Composite, *not* QuickTime Movie. That means the movie will be
created very quickly, with no additional compression. (This is bad
when you're making a video to dump to tape, but exactly what
you want in this case.)
Recommended third stage compression settings
- Behind the scenes, Premiere actually calling the SGI
dmconvert command-line program. You can do it yourself, which
I think is considerably faster for major crunching. The command-line
syntax has a somewhat high learning curve, but the man page is
complete. I (Tamara) spent some time trying to find the right tradeoff
between file size and image/sound quality. Here is the command-line
that settled on for one of my movies:
dmconvert -f qt -p audio,rate=44100 -p video,brate=100000,comp=qt_cvid,rate=10,squal=.5,tqual=.5 big.mov svelte.mov
That corresponds to the following settings:
- File format: QuickTime
- Audio rate: 44100 HZ
- Video bitrate: 1000 K/sec
- Video compression: QuickTime Compact Video == Cinepak
- Frames per second: 10
- Spatial Quality: .5
- Temporal Quality: .5
- I recommend transferring the raw files from moviola to radiance,
since dmconvert is all about CPU speed. The transfer time is
worth the resulting speedup. Note that Cinepak compression
times are still quite long: between 10 and 20 minutes to
compress a one-minute segment.
I have found that the file sizes for movies that are digitized from
tape are usually much larger than for movies that are created directly
from Premiere. For instance, the H3 video
clips of around one minute each range in size from 25MB to 47MB,
at quality level .5. In contrast, the direct-from-Premiere Constellation video one-minute clips range
from 4.4MB to 11.3MB, at quality level .99 I'm not really clear on why
this is so, I don't think it's operator error (although one never
The major tradeoff is legibility vs. download time. The biggest win
with file size is frame rate. 15 FPS results in files half the size of
30 FPS. I found 10 FPS to an acceptable setting. Temporal quality
controls jerkiness, spatial quality controls fuzziness. I found .5 a
reasonable setting for both, not much worse than .7. The movie looks
pretty scruffy around .2 or .3. To understand the file size tradeoffs,
the results from one of my tests was 25MB for spatial and temporal
quality of .75 vs. 9MB for quality of .2 spatial and .3 temporal.
(Both were 15FPS, and the segment was 47 seconds long.) My final
choice was 10FPS, .5 spatial and temporal quality, resulting in a 31MB
- You can use dminfo foo.mov to discover the settings used
to create most movie files.
The movie file should have the suffix .mov to be readable on
PCs. Don't bother gzipping the movie file, since it can cause problems
on PCs: the Cinepak format is highly compressed.
- Audio: don't bother tweaking the audio settings, since the amount
of space used is negligible compared to the video. (I also
could not find a way to tweak the audio bitrate without
completely messing up the speed of the audio track.)
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Last modified: Wed Jun 21 02:14:30 PDT 2000