Marvel G400 and MJPEG data rates

[conanian]

My box:
Athlon XP 1900+
384MB PC 133 SDRAM
Epox 8KTA3+ pro

HDDs:
Seagate U8 series 4.3GB (for Windows)
Seagate Barracuda 4 60GB
WD 600BB (Capture Drive)
(All linked thru a Promise Ultra 100 TX2)

Capturing program of choice: Virtualdub
VT version: 1.55
OS: Win ME

The problem:

I always set the quality of the MJPEG as "High." The settings window said the "High" setting would have a compression ratio of 6.6:1, and the data rate being 2.930MB/sec.

However, in actual capture, the "data" shown on VD was fall lower than that... often it started off at about 1530 kbps and would have the maximum of 1930 kbps... Why is the actual rate much lower than expected?

[Dr Mordrid]

Does the clip look good? IF so then it's likely the content wasn't that hard to compress.

Dr. Mordrid

[conanian]

Originally posted by Dr Mordrid
Does the clip look good? IF so then it's likely the content wasn't that hard to compress.

Dr. Mordrid

The quality was okey, given my source is PAL TV. However, Zoran tends to make the compression VBR?... Isn't the bitrate fixed?

[Dr Mordrid]

MJPeg isn't VBR in the sense that MPEG is (MPEG is much smarter) but its data rate can float according to the complexity of each frame and the efficiency of the individual codec when compressing it.

Remember that an MJPeg video is, at its essence, a stream of JPEG images; hence it's full name of MotionJPEG

An example of this size disparity according to image content can be seen if you create three 720x480 JPEG's with 50% quality: one black, one white and one an actual photograph.

In one series like this that I produced the white and black images were only about 12k while the actual photograph was over 60k.

Now...most videos won't have such stark differences from frame to frame or even scene to scene, but imagine even a small size disparity according to frame content propogating through a stream consisting of about 100,000 images.

Dr. Mordrid

[davpen]

You might also want to check that the lower data rate isn't due to dropped frames. Your motherboard looks like it is using a VIA chipset and and the PCI bandwidth problems of VIA are well documented on this forum. I know that I could never get full res capture to work with a VIA based motherboard and a Rainbow Runner G series.


Cheers,

David.

[Dr Mordrid]

Yes, this is true too. A large number of drops would artificially lower the bitrate. The VIA issue is also very valid and a royal pain in the rear.

Dr. Mordrid

[conanian]

Originally posted by Dr Mordrid
Yes, this is true too. A large number of drops would artificially lower the bitrate. The VIA issue is also very valid and a royal pain in the rear.

Dr. Mordrid

The drop rate is actually very low, close to 10000 frames per drop.

However sometimes very serious full screen artifacts would occur, and I don't know if it's related to the VIA...

A screenshot of the artifact should be sent later.

[conanian]

First of the 3 kinds of artifacts...

[conanian]

The second...

Note: The source is from TV. However, the repview was OK-- actually the TV reception was at a very high standard.

[conanian]

The last of the 3...

[daniele greco]

I found out this "old" thread", I apologize for this "pace back to the past", but, sI use 1.55 VT and 6.28 DD, and I am having the same problem with the artifacts in the frames exactly as the kind of those showed by conanian in the post, and I could not find any other post with some suggestion for a solution or idea
I don't know what is the cause: I re-installed the VT1.52, but with that version I had other worse artifacts from time to time, so I prefer to use 1.55 VT.
What I noticed is that the artifacts occur excatly at scene changes, even if not 100% of them.

What is possible to do?
Thanks to everyone will answer.