Green flashes ?????

[Andrea]

Is there anyone that have correct the bug of green flashes in TV output ?

[Rick6612]

Hi Andrea,

I have once or twice had a problem with green flashes during playback of video. The problem was caused by the video data rate going to high for the codec to handle.

In one case, it happened when I was shooting video in a darkened auditorium, and a lot of people started taking flash pictures. The rapid flashing in the video seems to drive the Matrox codec crazy.

The solution was to recapture that section of the video at a slightly lower compression quality setting, forcing the data rate a bit lower.

Rick

[fluggo99]

Do you happen to know what that data rate is? I'm having trouble after rendering a video project; I'm wondering if setting the data rate in the Ulead render options dialog will have any effect.

[Rick6612]

Hi Flugo99,

The maximum data rate the Matrox MJPEG codec can handle is around 3 MB/second. I don't know exactly what it is. As I understand it, it has something do with the hardware having a 128KB buffer which the compressed frame has to fit into. If any one frame exceeds 128KB, it will cause the green flashes... I'm not certain that what I just said is 100% accurate, but it is somewhat close to what I have read...

Anyway, there is supposedly a patch you can download from Ulead's web site for MSP 5.2 which is supposed to correct some problems with excessive data rates during rendering. You may want to check into this if you are having problems.

Rick

[DrMordrid]

The effect you're noting is a common one with MJPeg because it provides poor data rate control. Since the size of any frame is dependant on the content of that frame data rate overruns are common.

Because of this you might set up the 6.6:1 rate of 3.102 mb/sec but actually will see 3.3 or 3.4 mb/sec in the capture report.

One more reason MPEG-2 and DV are coming on strong: they both have strong data rate controls.

Dr. Mordrid

[Grigory]

In my tests, these flashes could occur on high contrast and high level of fine details scenes. To avoid them you can:
1. Reduce the contrast settings for dangerous parts of movie before starting capture. Reducing brightness may also help. Sometimes, you have to make the movie unacceptably dark to get correct playback.
2. Try to capture with datarate reduced by one step. You can also try to find some intermediate value of datarate, modifying the quality value in Registry.

In my case, I was looking at frame size in Premiere 5.1. It can show the size of individual frame. What was found:
a) the frame size below 128 kb is good.
b) the frame size of 129 K may be good, but may produce green flash
c) If the frame size tends to go over 132 kb, i.e the datarate curve looks increasing up to this value, the frames that could be >132 kb are dropped on capture stage. Several frames with sizes >128 K have green flashes.

To repair green flashes you can try to re-compress problematic frames with morgan codec and set the datarate below 128k per frame. Or, you can re-render with Matrox codec, which in this case will use software part (no green flashes in decompressed frames) for decompression, and, as some people here said, can produce good frames on the output.
For problematic transitions (like adding random noise particles), you can try to apply some smoothing filter like Gaussian blur.
You also can try to capture from composite input to reduce the probability of too high datarate frames.

Grigory

[CAVEY]

Hi All

This seems to work with hihg data rates.

I have been experiencing the green flash problem when editing videos since late 1999 when I changed my mother board and processor. The current mother board has a VIA PC133 chipset and PIII 500 processor, old mother board BX440 and overclocked PII 350.

I think I may have found a solution to the problem, I have only tested this for about an hour so far and have not experienced and green flashes, so it definitely helps.

I downloaded G200CLK from the MURC site just to see what it did and whilst playing I noticed one of the default settings seemed to be odd.

Using the /3 option the default setting for my system are 84.38, 112.50, 84.38 (equivalent to /3 2 1 2).

I am now using G200CLK /3 2 2 2 (84.38, 84.38, 84.38) in my startup and this has helped if not cured the problem. So I am using G200CLK to slow my system down slightly instead of speeding up as it was intended for.

Any feedback of your experiences trying this fix or further tweeks to improve on it would be much appreciated.

Matrox Tech, if this does work can we have in the drivers soon please?

colin.avey@themutual.net