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Scott Tashman, Ph.d.
11-12-2003, 06:33 AM
Quick comment:

Be careful with terminology with respect to video formats. AVI and
Quicktime are "containers" for video - they are not specifically linked to
any compression format. AVI and MOV files can be uncompressed, or
compressed with a variety of methods (mpeg-2, mpeg-4, cinepak, DV, Windows
video, etc.).

Most compressed formats can be imported into professional-grade video
editing programs (Adobe Premiere, Avid Xpress, Apple Final Cut Pro, etc.)
and edited, and there is nothing inherently bad about mpeg compression.
But, different compression algorithms (and degrees of compression within an
algorithm) will introduce different kinds of errors for quantitative
analysis. Also, uncompressing, editing and then recompressing files creates
additional artifacts.

I disagree with the negative comments about firewire acquisition. The
compression used for DV-format video files is mild, and probably well-suited
for quantitative analysis. DV-format files can be retrieved from any
mini-DV camcorder with a firewire output, and you get the same quality video
whether you do a live firewire import from the video camera, or play back
the tape via firewire after recording is done. Also, inexpensive versions
of the professional editing programs are available for dealing with
DV-format video (e.g. Final Cut Express, Avid Xpress DV). Camcorders with a
progressive-scan mode are preferable, to eliminate interlace issues. DV
imports create large video files, but recordable CDs and DVDs are cheap
these days. I would be wary of using any additional compression for
quantitative applications unless I had performed an analysis of the effects
of the compression on measurement accuracy.

Scott

_______________________________
Scott Tashman, Ph.D.

Head, Motion Analysis Section
Bone and Joint Center
Henry Ford Hospital
2799 W. Grand Blvd, ER2015
Detroit, MI 48202

Voice: (313) 916-8680
FAX: (313) 916-8812
E-Mail: tashman@bjc.hfh.edu

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