MPEG-2 Encoding with the Marvel

[Trinity]

If the ATI AIW card only uses software for
MPEG-2 compression, is it possible to have
the Marvel do the same with software?

In other words, with the Marvel, is it feasible that I could have the same MPEG-2 video capture capabilities as the ATI with the additional option of using MJPEG if I so desire? If so, from the standpoint of video
capture, why would anyone choose the ATI over
the Marvel (ignoring price and the fact that the ATI has better DVD playback quality)?

[CMB]

Id just like to rebuff your testimony about the DVD playback, ive seen the ATI's on a friends 21 inch monitor and allthough its good The marvels is equally as good, and the tv output it if anythying better. My referance of quality is the DX3 card from creative labs...
just thought id chip in :O)

[DrMordrid]

You would use the Ligos MPEG encoder that is bundled with the Marvel to transform MJPeg to MPEG-2.

Actually MPEG-2 IS NOT a very good editing format unless your card has the C-Cube codec chip on board. The AIW-128 Pro does not.

The AIW relies on the Ligos GoMotion codec which works, but is slower and less effective because is is a software solution.

Like any software only solution it places heavy burdens on the system to do it's compression and playback. As such it requires a PIII-500 minimum to do full rez work. The Marvel, DC10 and others that use hardware compression can do this with just a Celeron 300.

Dr. Mordrid

[Phire]

First of all, the ATI AIW does Software MPEG-2 Encoding, and i've heard its not even really that good - As you can see in the comparison chart that Matrox has what the differences are between Software and Hardware Encoding, visual quality is major.

Secondly, MPEG-2 has a even larger filesize than MJPEG.

Third, MPEG-2 is used for really high quality video, it'd be pointless to use it for something for capturing off TV or anything of the sort. It can be however used for Digital Video Cams and/or actually using Film and doing straight to MPEG-2.

[Trinity]

My comments on the DVD playback quality
between ATI and Marvel were only based on
reviews which cited hardware support on the ATI for DVD playback which the Marvel does
not have. But I agree...after playing a few
DVD's on my Marvel G400, I can't see why
anyone needs to add DVD hardware unless you
have a slow CPU.

As for MPEG-2, I really meant, "Is there a
way to achieve real-time MPEG-2 capture with
the Marvel?" Doesn't the ATI do this in real-time? I don't intend to use MPEG-2 for editing but rather to save disk space when capturing TV programs that are meant to be watch and erased (where quality isn't important). This would save an additional MJPEG -> MPEG-2 encoding step. I have a PIII-450 running at 600 so CPU speed should not be a problem.

PS. I encountered an error while encoding
Matrox MJPEG to MPEG-1 using the Ligos encoder. A message "DC value out of range"
popped up when it was only 60% done. Altering various encoding settings didn't help. An error also occured with the Xing Encoder. I'm not sure how I would deal with this if it happened on stuff I cared about instead of test material.

[DrMordrid]

To do realtime MPEG-2 capture you should have a capture board with the C-Cube chipset on it. Software doesn't cut it.

Right now they are rather expensive since the only ones are the RT-2000 (not out yet), DC-1000 (crappola) and the FAST 601 (OK so far). The cheaper versions are still in development from all makers.

As for the problems with encoders: this sounds like a setup problem on your machine. I use Ligos and Xing! and have not had problems with either under Win98 or Win98SE.

Have you tried moving your TMP and TEMP assignments to a directory on your capture drive? The temp files may be getting large enough to cause your boot drive to fill up. This can cause problems with MSPro and Premiere so....

Dr. Mordrid

[Grigory]

For better understanding, read mpeg2 FAQ at http://www.mpeg.org

I am surprised to see a lot of incorrect or not precise statements about mpeg here on the forum.

1. ATI uses I frame mpeg that is equivalent to MJPEG, except the headers. The quality should be about the same at the same data rate. Editing is not possible at the current state of editors. I don't think this is due to mpeg format, but because the manufacturers have not enough will to include I frame mpeg editing support into editors. So, ATI solution is not for video editing.
2. Higher (or same) quality at lower datarates is possible only for IPB mpeg. What is it? Shortly, its is motion-predicted MJPEG. For P and B frames, the encoder tries to predict the changes, and then compresses into DCT frame only remaining difference. Where is quality gain?

I used DV footage, LSX encoder at simple vbr mode and 5500 kbps. and then used bbmpeg to get frame sizes. The result was:
I frame average size - 34532
P frame average size - 31454
B frame average size - 23795

in bytes

The image quality cannot be better than the I frame quality - 35kb per frame, which is 875 kB/sec.
If you make I frame mpeg at the same average datarate of 5500 kbps, the frame size is 29 Kb, so the datarate is exactly 725 kB/sec, in MJEG-equivalent format. This is 1/4 of what RR_G can produce.
So, in my tests, using DVD-style mpeg2, you can reduce datarate by ~18% at the same image quality level.
Using CBR mode, you can get the following values:
I frame size - 38578
P frame size - 35927
B frame size - 19947

with visually lower quality.

I have to say that the video quality was much better than MJPEG at the same data rate. The possible explanations are:
a) better quantization matrices used for mpeg DCT compression.
b) adaptive quantization used in mpeg compression.

Mpeg description does not have any other hidden reason why mpeg is better than mjpeg.

I tried also Pixeltools encoder and bbmeg itself - the digits look very similar.

Playing with quantization matrices you can change the quality at a given data rate, and find optimal matrices for specific movie.


Conclusion:

Due to better I frame compression, the quality of I frame mpeg2 approaches the quality of RR_G mjpeg at ~50% of mjpeg datarate. Temporal compression can reduce the datarate at given visual quality by ~20 more. Finally, you can expect equal image quality at 40% of mjpeg datarate: 8 mbps (1 MB/sec) IPB variable bitrate mpeg2 is approximately equal to 2.5 MB/sec mjpeg from RR_G.

Last note - I was comparing quality, starting from interlaced full size DV footage: in the case of DVD titles with typically film frames inside, the quality of mpeg2 may be significantly better.

Grigory

[geralda590a]

I have a g400 and a g200. MGI VideowaveIII has settings for automatically capturing direct to mpeg 1 from the g400 after it is installed. and can be custom setup to capture to mpeg II. When installed with a g200 it only has avi mjpeg options. it uses a codec supply by LSI---same codec but with more options than the one included with g400---and it does realtime captures and not just conversions.