Increasing latency
 

I am using v1.2.1490.0.

I have always been aware of the slight latency between what the camera is recording and what I see on the laptop. I'm quite comfortable with why it happens and it doesn't cause me any concern.

However, I noticed on my last two shoots that the latency INCREASES during long recordings (15 mins +) to the point where it's up to 20, 30, 40 or more seconds! I've never noticed it before because I haven't ever recorded clips longer than a few minutes. These were interviews, hence the longer shot length.

In another thread someone mentions the "over 1Gb RAM" problem but I can't find any explanation of what this actually is (here on at Serious Magic's forum). I have 2Gb. Is this a possible cause?

Other tech details: 3.4GHz P4, 2Gb RAM, recording to internal 7200rpm drive, no other devices using the f/w bus. XP Pro SP2. A/V running in the background, no other major tasks. Nothing has changed to the above since I installed the 1.2.1490.0 update a few months ago other than new programme installs (namely Vegas 7).

Any and all suggestions positively welcomed!

Ian . . .

Bump.

Hate doing that, but I'm keen to know if anyone else has had this problem and if so, is there a way to resolve it?

Cheers!

Yep have it too on 1.2 and 2.0
Laptop 1GB RAM, P4 hypertreading, 128Mb ATI

Hi Marc,

Does your latency get REALLY bad as time goes on - like up to ten, twenty, thirty seconds?

Yes Ian, when I stop the tape it keeps on going

Er, another bump. Anyone from Serious Magic here?

Are you seeing a lot of alert flags in your recordings? Alert flags are the red and yellow indicators in the audio waveform showing potential audio or brightness problems. They are controlled by the DV-QM module.

Usually, in normal use, you shouldn't see many of these alerts, but if you have the sensitivity set too high, you can accumulate a large amount of alerts in a single clip. These alerts use system RAM, so if you are doing long recordings, this could cause the system to become sluggish, and increase latency.

To correct this, turn off the alerts in the DV-QM, or set the sensitivity so that you aren't getting tons of alerts in a few minutes.

If you are recording HDV, then this increasing latency is a result of CPU overload. The remedy is to throttle back DV Rack's MPEG decompression through one or more of the following settings in the Field Monitor Menu:
* Visible Frames
* MPEG Resolution
* MPEG Frames

Karl, Mark, thanks for the replies.

I'm recording SD, not HD. I'll check the point you raised, Karl. That sounds like a likely candidate! Thanks for that.

So, this is nothing to do with the "over 1Gb" thing then? Can you please describe exactly what that is and how it manifests itself? I can't find any details anywhere and as the issue is only fixed in v2 and not v1 (and I don't have the means to upgrade at this time) I'm keen to know if/how it is affecting me.

Many thanks,

Ian . . .

The 1 GB RAM bug involved the Field Monitor and other analytical tools freezing after a certain period of time. With DVCPro footage on a dual core processor, the period was typically about 30 seconds. This bug was theoretically possible with SD and HDV video and on single processor systems, but it was apparently a certainty with DVCPro on a dual core system that had more than 1 GB.

To repeat Karl's notice, the update that we released today resolved this problem.

Thanks Mark, I'm happy to see that it is unlikely to affect me.

Which is fine for those who are upgrading to v2 but not so good for those who aren't/can't, like me!

Thanks again for the detailed answer.

Ian . . .

Sorry to be a pain but I'm not quite sure I understand the levels in the DV-QM module.

Mine show (video) Level 97%, Area 5%, Duration 1; (audio) 12. I guess these are the default values as I haven't knowingly changed them since installing.

Are these optimum values?

I will experiment with turning the meters off but it would be a shame to lose functionality.

The values vary depending on what you are trying to monitor. What type of alerts are you getting in your clips? Yellow alerts indicate a brightness condition, dark red alerts indicate an audio level jump (like a "pop",) and bright red alerts indicate audio is so loud that it's overmodulating, or distorting.

The current Video settings will give you a yellow indicator if 5% of the screen gets above 97% brightness for even a single frame. If you are getting a solid yellow bar in your clips currently, either iris down, or adjust lighting. You may also want to increase the area to more like 15% or 20% so small areas of over-brightness won't set off the alert.

The Audio indicator means that if your audio jumps up by 12dB, it will flag that frame of the clip. I would probably increase this to 20dB or 25dB to make it less sensitive. Or, if your audio is uncontrolled, I would just turn it off. This indicator is mostly used for controlled environments, like interviews with lavalier mics. If you are using the camera mic, then you're probably getting a lot of meaningless dark red flags in your clips. Just turn it off in that case.

Thanks Carl and Mark for the info.
Yes it happened by capturing HDV footage.
I will install the update, thanks for solving it.