Hi all,

I'm using IRIX SGIs to capture camcorder and VHS material to MJPEG
files and them convert them to other formats on a PC. So far, I have
found that if I capture as default SGI MJPEG, codecs such as the PIC
codec seem to treat the fields as frames, so one sees a half-height
squashed image. But if I capture as MJPEG-A (using an O2 in this case),
the PIC codec can handle it just fine using the QuickTime player. One
can then use RAD Video Tools to convert away from .qt format, and
so on.

However, one of the SGIs I use (R10K Indigo2 with IMPACT Compression)
cannot capture as MJPEG-A, so I was wondering:

- what is the difference between an MJPEG and an MJPEG-A video
stream? Does the addition of the Alpha channel (I assume that's what
the A means) actually alter the JPEG values for the encoded pixels?

- is there an easy way of converting MJPEG to MJPEG-A? If so then
I would then have my ideal video system: ultra-reliable capture
using an Indy, Indigo2 or Octane, then convert to MJPEG-A and
lastly convert to MPEG2 or whatever on a PC.

On the same subject, does anyone know why the PIC codec mistakes
fields for frames in an MJPEG stream? I haven't tried the Morgan
codec yet; does anyone know if Morgan behaves the same way?

For those familiar with IRIX video capture, I'm using dmrecord
with 25Mbit/sec bitrate, uncompressed stereo 16bit audio, 2-field,
JPEG, device=impact, engine=impact (this also would apply to an
Octane with Octane Compression, or an older Indigo2 or Indy with
CosmoCompress). IMPCOM can capture as good as 2:1 at 4:4:4:4,
so it would be great to work out a way of converting such captures
using a PC with a suitable codec/tool combination. Plus, if the MJPEG->
MJPEG-A conversion process is fairly trivial (ie. doesn't involve
re-calculating the JPEG values) then one could use O2 ICE to do
it in hardware, ie. fast.

Any info would be most appreciated!

Cheers!

Ian.