Capture quality and mpeg2-conversion.

[OleJuul]

Hi there. I consider buying a marvel400, but I have some questions about video capture...

I'v heard that maximum bitrate is 3 mb/sec. But what is the lowest bitrate (highest compression) in full screen capture? And what is the quality of low-quality like compared to the high-quality?

Second, how much is the filesize reduced when converting mjpeg to mpeg2? Will a full-screen clip captured with high mjpeg-compression and converted to mpeg2 take less space than a the same clip captured with low-compression and converted to mpeg2?

Third, is the mpeg2 output of the converter IBP-frames? How long time does the conversion take?

Fourth, is there any way to reduce filesize further, im thinking of an other format (like asf?) or an other converter program?

Finally, there must be some softeware which can capture mpeg2 realtime, thereby skipping the conversion. Does anybody have experience with such programs? How much cpu-power is required for direct fullscreen mpeg2-capture?

Hope you can answer some of my questions. Thanks in advance.

[Luigi Brambilla]

First of all, you have to decide what will be the final destination of your clip. This is a basic start, which involve different products.
Basically, you will use the G400 card to capture video in its first digital form, then ... it's up to you.

For an overview of sw products, this site can be a good start.
http://www.bernclare.com/mpegprod.htm

Follow the tips on this forum regularly, or scroll through the old ones. They helped me a lot to understand this 'vaste' argument.

Have fun!

Luigi

[DrMordrid]

1. The lowest Marvel/RR-G/RRS data rate for 704x480 captures is 1.344 mB/s at 16.5:1 compression. The perception of the quality will depend heavily on the quality of the source. I would not recommend the lowest quality setting if you plan on adding titles or graphics however. Use the highest setting for that.

2. MPEG-2 encoding with the bundled Ligos LSX-ME encoder uses a 4096 kb/s (video) bitrate. To a big degree the compression ratio depends on the content of the source file. Generally it runs 40:1 to 70:1, averaging about 50-60:1 when using 3.102 mB/s MJPeg sources.

3. I'm not for sure of the GOP sequence used in the Ligos LSX ME version but the sequence shown in the help file is I BB P BB P BB P BB P BB.

If you upgrade to the full version of Ligos (you get a break if you're a Marvel G400 purchaser) you can set whatever GOP sequence you want.

The conversion time again varies with the content. It can run from 3:1 up to 20:1 (or more) with the average being about 12:1. Remember, this is high quality software rendering and that takes time.

4. ASF is a streaming format and not really intended for use as a storage format. Use it for web video publishing and leave the archival storage to formats made for that purpose.

5. If your video card can capture using RGB or YUV you can use Uleads Video Studio 4.0 to capture MPEG-2 files.

I've never tried this with the Marvel G400 but it can capture RGB natively and YUY2, a "dialect" of YUV, with a registry hack.

The rub is you need at least a 500 mhz PIII or Athlon level processor to do this. PII's, Celerons or K6-2/3's can't cut it.

Dr. Mordrid


[This message has been edited by DrMordrid (edited 17 January 2000).]

[OleJuul]

Thanks a lot for your replies.

So the Ligos encoder will only make full screen mpeg2's at 4 mb/sec?

The AIT-'all in wonder' capture 640x480 at less than 0.5 mb/sec...
(http://www.ati.com/na/pages/faq/aiwfaq.html)
The picture quality might be a little better on marvel, but 8 times more diskspace?

The ATI-card can capture on the fly, using a PIII, the marvel conversion time takes more than 3 times the playtime?

Why should I go for the marvel over ATI for video capture?

[ccc]

The ATI uses software MPEG2 compression, so u need a fast processor to encode at 640*480.
The quality of the MPEG2 it produces is less than that of the Marvel with MJPEG.

Because you can capture RGB like DR .Mordrid said, It lets you do +- the same as the ATI with the MArvel: RGB capture then Software MPEG2 compression, if you have a fast CPU...

Never tested though ...
Anyone ?