Correct timebase for DVCPro HD

Posted by nicknasty 
Correct timebase for DVCPro HD
February 12, 2008 03:05PM
I recently shot some footage with Panasonic P2 system to 720P 25 (for PAL distribution). As a first time user I was very pleased with the picture quality but the problems started when I burned the client a DVD (PAL) copy of the dailies.

There is a very distracting stutter effect going on aprx every 1 second or so. I can see from the TC burn that the DVD actually skips frames here and there along the way. (QT and FCP show no skipping) What?s going on?? The DVD was authored from self contained QT using VisualHub. It does get better in the end. No skipping anymore.

After review I noticed my sequence timebase is set to 50 fps (Blackmagic Intensity easy setup). It seems to work perfectly except for the DVD stutter. Re-rendering my sequence back to 25 base seems to take a whopping 8 hours so it is clearly not as efficient as the previous 50 base which too less than 4.


While waiting for the new render to finish, my questions are:

- What?s the difference between 25 and 50 fps in sequence editing timebase. They both seem to play 25 fps material in real-time (no over/undercranking)? Why is there such a big difference in rendering times?

- Is the stutter effect (on the DVD) caused by editing on a ?wrong? (50) timebase?

- If not, can anyone guess the mostly likely culprit? Mpeg keyframe interval, wrong codec etc?
Re: Correct timebase for DVCPro HD
February 13, 2008 08:54AM
Anyone????

After 8 hours I ended up with a bunch of s..t. Changing the sequence editing timebase to 25 did not help. In fact, FCP crashed immediately after I tried to play the rendered sequence. I am baffled... what is this 50 fps editing timebase stuff?
Re: Correct timebase for DVCPro HD
February 13, 2008 10:25AM
Sorry, but DVCPRO HD and PAL work in unique ways that I am not experienced with. Otherwise I would have commented.


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Re: Correct timebase for DVCPro HD
February 13, 2008 02:02PM
What's interesting about dvds, is that even if the fields are placed wrongly, they somehow can manage to read it right.

Hmm... I've only worked with Dvcpro HD 720p once, and on 6.0.1 before the 50fps timebase was a feature in final cut, and later upgraded to 6.0.2 and the project somehow continued again...

What's confusing about 720p, is that i was working with Dvcpro HD 720p50 but at 25 fps, progressive. I believe the "50" comes from the 50 megabit resolution (as the file size seems similar to dvcpro50). The timebase of 50fps, i believe, is to allow the same footage to be displayed both at 25 fps (progressive) as well as 50i (interlaced) without a loss in quality. Also it allows you to slow down clips (at 25fps) down to 50% without quality loss.

And yea, it is friggin confusing! On 6.0.2, by default, a 720p50 timeline switches automatically to 50fps, and i was wondering for a while why it didn't display at all in my broadcast mon.

Then again, I think you have to convert 50fps to 25fps for dvd encoding.

What is specified in your clip codec/framerate in the browser? Your sequence setting should follow that.
Re: Correct timebase for DVCPro HD
February 14, 2008 05:19PM
Thanks strypes, there is more to follow;

After multiple crashes, lost preferences and so forth (Almost like few years and several versions ago!) I finally realized what to ask: What is the preferred way to do down-conversion from DVCPro HD to DVD 16:9 PAL?

Different options:

1. Export self-contained QT, default settings (DVCPro HD 720p 50). Import directly to DVD studio and let it handle mpg conversion

2. Export self contained QT, PAL 16:9 settings. Import that to DVD Studio Pro

3. Export using compressor, DVD MPG2 settings

4. Something else


If you know how to do this, PLS let me know. I am loosing my faith?
Re: Correct timebase for DVCPro HD
February 15, 2008 01:42AM
What is the native timebase that your footage is shot in?

you can check it by hitting command 9 over a clip and checking the framerate. Also clips that are compatible with your sequence setting needs no rendering (grey/no render bar as opposed to a light green/red/orange render bar)
Re: Correct timebase for DVCPro HD
February 15, 2008 12:06PM
Clips need no rendering on their own and settings are OK. Footage displays nicely and everything is semi-ok. I was even able to create a decent DVD using Compressor.

That Blackmagic Intensity card sure crashes my system a lot. If my Mac goes to sleep, it's time to re-boot . Not too cool
Re: Correct timebase for DVCPro HD
February 15, 2008 01:51PM
Your mac is not supposed to go to sleep if you're working with media. Btw, are you running leopard? it happened a while ago. Turned the darn thing off (and i think i upgraded to 10.5.1) and didn't have a problem after that. And no man, i'm working on the dinosauric Blackmagic SP. (yes, i know, but it's not my mac, you see).

Good to hear that you're able to get your DVD done. If your clips need no rendering, you're all good to go for the edit.

So, what codec were you on specifically? Was it 720p50@25fps, 720p50 (at 50fps) or 720p25? If you were on 720p50, did you tweak any setting to have compressor convert it down to 25fps?
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