From: Milton Aupperle <milton@outcastsoft.com>

Date: February 10, 2010 2:03:54 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] AstroIIDC & time stamping

Hi Ralph;

On 10-Feb-10, at 11:36 AM, rmegna54 wrote:

Milton,

I am working on an occultation project and thought that AstroIIDC and a Firewire camera would make a good solution given that your software can time code the frames. However, I wanted to get your view on two things:

1) Do you have any idea how accurate the clock is on your average Mac?

Nope. It varies a lot. Most of my Macs seem to loose about 1 to 2 seconds per day though.

Asked another way, if I have sync'd my Mac to a Internet time server, what is its fidelity to "true" time?

Astro IIDC will use the current Mac Clock Time when you begin recording as the initial "Hack" time. After that it uses the FireWire Cycle time which is accurate to +/- 0.125 milliseconds to determine frame arrival time. So the only really variable thing is the start time and if you have it check the date right before you begin recording, it should be reasonably accurate.

With OSX 10.4.x, Apple used to print off the time offset change in the console log when you turned off and then back on the "Set date & time automatically" check box in the "Date & Time" panel, so that you could gauge how off your Mac might be over a given time period. They have removed that in 10.5.x and higher of course and impaired the latency of the console app in the process.

I wrote out some work around methodology for this using the terminal.app to change the frequency of the not clock server, but not surprisingly I can't find it in the Yahoo's useless crippled "search engine" for Astro IIDC Groups anymore. It involved using the terminal.app, and the ntpdate command with a time server like "time.apple.com".

2) AstroIIDC appears to display time codes in standard pro video format - HH:MM:SS:Frame.

Actually we don't display anything. That's the Apple Time Code Track displayed in the movie.

While it is simple math to convert this "time" I was wondering if it were possible to have an option to display milliseconds (MS) rather than frame number.

No it's not possible. Apple controls the display of the time code data in the movie, not us.

HTH..

Milton aupperle