Is MJPEG lossy or lossless?

[Eddie]

As the subject - and mostly in this situation:

I recorded something using PC-VCR, from cable - set to MJPEG compression.

Great. I recorded two clips, now I basically want to put em together (little
fade in between both).

Ulead Mediastudio Pro 5 VE : put em there, make a little transition. Oh,
project properties: set to same resolution (352*240) - and the FPS.. well, I
look at the file properties of the originals, and see 29.996 (whatever that
decimal number is) so when I go to CREATE VIDEO I also put the 29.9.. not
30fp/s. I look at the compression tab - it's on MJPEG, where the sliders are
both to the right.

Now the saving of the file was quick (which to me looks a lot like the fact
that it must've just used the untouched parts from the original file...) -
HOWEVER I'm not 100% sure..

Is my video editing causing loss of quality, a la JPEG? Or is MJPEG, with
a G200 lossless while I edit with MJPEG? I mean there is a 'quality' setting -
how do I make it so once compressed from the source - all editing (unless I
specifically want to) is done in a NO-LOSS fashion? In general I'm happy with
how compressed the files are by mjpeg in the first place - and whenever I'll
be done with video editing, I'll want to compress using other codecs anyway...

Thanks if you can help with your comments,

Eddie

[Jeff Lindstrom]

In article <7j4usk$833$1...@new-news.cc.brandeis.edu>, REMOVEe...@brandeis.edu (Eddie) wrote:

> I recorded something using PC-VCR, from cable - set to MJPEG compression.

> Is my video editing causing loss of quality, a la JPEG? Or is MJPEG, with

> a G200 lossless while I edit with MJPEG? I mean there is a 'quality' setting -

JPEG is a lossy medium. Basically, it works by taking an 8x8 pixel
square and determining the average. Then it takes the averages of four 4x4
pixel squares and compares those averages against the 8x8 average. This
process can continue down the line to 1x1 pixel squares.

You can set the compression (i.e. how far into the matrix everything is
averaged and compared) to control image quality. The actual amount of
compression you set will determine final quality (more compression means
less quality on complex images).

Standard television images move up to 1 megabyte per frame or 30
megabytes per second.

The Marvel's compression range is 4.3:1 on up to 10:1, so even
maximum-quality images will have some loss.

However, composite video I have captured at maximum quality looks much
better than video tape (and I have a 4-head ProScan unit) and is quite
sharp. I have read that S-Video edited on the Marvel and re-recorded to
S-VHS was almost indistinguishable from the original.

> how do I make it so once compressed from the source - all editing (unless I
> specifically want to) is done in a NO-LOSS fashion?

There is no additional compression during the editing process. You can
set various compressions by selecting codecs in the resulting AVI files, if
that is your final destination. If you record to tape, you only have to be
concerned with the limitations of Composite compared to S-Video.

Jeff

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