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Chapter 4: Digital Video on the Osprey-300
The dvsd format comes in two flavors - video-
only, and audio + video interleaved. The audio
+ video data rate is slightly higher than the
120,000 or 144,000 bytes per frame quoted
above - for NTSC it is about 129,000 bytes per
frame, or about 3,866,130 bytes per second.
The dvsd format can be captured directly to
AVI files. There are two subformats - Type 1
and Type 2. The Type 1 format stores the audio
+ video data as a single stream. The Type 2
format stores the audio and video data as two
separate streams. The Type 1 format is more
compact and efficient but is not backward-
compatible with Video for Windows. Osprey’s
SwiftCap application, as described below,
currently supports only the Type 1 format. With
other suitable applications the Osprey-300 DV
connector can capture in either format.
Several additional DirectShow filters support the
DV capture module.
The most important is the DV Video Decoder.
This filter accepts dvsd video-only streams as
input. As output it delivers an uncompressed
YUY2 stream at full, half, 1/4, or 1/8 size. This
filter is always used when rendering video.
When capturing video without compression, it
is normally not used, but could be useful for
capturing quarter-sized or 1/8-sized video, at
some savings in data rate. (Note that the full-
and half-size options would increase the data
rate to no purpose.) When video is captured
with compression, a DV Video Decoder will be
placed in front of the compressor, to deliver the
YUY2 input that the compressor uses.
The other specialized DV filter commonly used
in capture is the DV splitter, which accepts a
dvsd audio + video interleaved stream as input,
and outputs dvsd video-only on one pin, and
standard uncompressed audio on the other.
Following the how-to description of SwiftCap,
there are some sample DirectShow graphs that
show some of the ways these components can be
connected together.
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