Quantcast VirtualDub - constant frame rate vs. variable FPS? - digitalFAQ Forum
Go Back    Forum > Digital Video > Video Project Help > Capture, Record, Transfer

Reply
 
LinkBack Thread Tools
  #1  
01-10-2014, 02:43 AM
Zerowalker Zerowalker is offline
Free Member
 
Join Date: Dec 2011
Posts: 119
Thanked 5 Times in 4 Posts
I know that when you capture, you are pretty much never going to get a constant FPS, the clock sync between devices are never precise and you will never get that 30fps you are supposed to.

However, i am wondering, is it possible to capture Variable FPS with Virtualdub?

I know it should be possible to capture, i can do it in Graphstudio, but in Virtualdub it wantīs to always set a FPS and then play it to that later.
Reply With Quote
Someday, 12:01 PM
admin's Avatar
Ads / Sponsors
 
Join Date: ∞
Posts: 42
Thanks: ∞
Thanked 42 Times in 42 Posts
  #2  
01-10-2014, 03:53 AM
lordsmurf's Avatar
lordsmurf lordsmurf is offline
Site Staff | Video
 
Join Date: Dec 2002
Posts: 11,685
Thanked 2,138 Times in 1,839 Posts
I'm not aware of any such error -- and I do mean "error", not "feature". Because that's what it would be. No TV (or even a streaming player) could ever play back such a problematic video. It expects (and therefore requires) consistency in the video stream. The signal locks to this, and is how the stream self-audits itself. For example, the ability to drop frames, or the ability to sync audio.

True, no capture is ever 100% perfect to the framerate, but that's because of the chaotic nature of analog video. However, it is close. For example, a brief few frames may be 29.971 or 29.969 in stead of 29.970.

Once digitized, it is a perfect 29.97001 frame rate (or whatever it is).

Like pi (3.14159...), I think the actual math for NTSC video is imperfect with an enormous decimal place.

- Did my advice help you? Then become a Premium Member and support this site.
- For sale in the marketplace: TBCs, workflows, capture cards, VCRs
Reply With Quote
  #3  
01-10-2014, 05:08 AM
Zerowalker Zerowalker is offline
Free Member
 
Join Date: Dec 2011
Posts: 119
Thanked 5 Times in 4 Posts
True, but mine isnīt so close that it isnīt noticeable.
To get it as good as possible, i have to save it at any framerate, disable all resync, drop frames etc.

Then use the Time Log that Virtualdub can give you at the end, and sync manually.
That way i will get the best result with no dropped/inserted frames or desync.

But for my problem, it isnīt actually in Analogue i am having trouble, but itīs my Webcam.

If i choose 30fps, it will be at an average rate of 29.874, which is very far away, so the only way i can get the correct speed is to tell it afterwards and change it, or save it in a Variable Framerate, meaning it will save in the framerate that it has in the end, to have the correct speed throughout the video.
Reply With Quote
  #4  
01-10-2014, 05:23 AM
kpmedia's Avatar
kpmedia kpmedia is offline
Site Staff | Web Hosting, Photo
 
Join Date: Feb 2004
Posts: 4,314
Thanked 370 Times in 339 Posts
If it were me, I'd just get a different webcam.

- Did my advice help you? Then become a Premium Member and support this site.
- Please Like Us on Facebook | Follow Us on Twitter

- Need a good web host? Ask me for help! Get the shared, VPS, semi-dedicated, cloud, or reseller you need.
Reply With Quote
  #5  
01-10-2014, 05:27 AM
Zerowalker Zerowalker is offline
Free Member
 
Join Date: Dec 2011
Posts: 119
Thanked 5 Times in 4 Posts
The problem is, how do i know that others arenīt the same.
Also, 25fps seems to be at about 25fps, so itīs 30fps that "fails".
Reply With Quote
  #6  
01-10-2014, 11:38 AM
NJRoadfan NJRoadfan is offline
Premium Member
 
Join Date: Sep 2010
Posts: 1,134
Thanked 350 Times in 287 Posts
Quote:
Originally Posted by lordsmurf View Post
Once digitized, it is a perfect 29.97001 frame rate (or whatever it is).

Like pi (3.14159...), I think the actual math for NTSC video is imperfect with an enormous decimal place.
Its technically 30/1.001.

As for the webcam, buggy drivers can drop frames silently without VirtualDub even knowing about it.
Reply With Quote
  #7  
01-10-2014, 04:02 PM
Zerowalker Zerowalker is offline
Free Member
 
Join Date: Dec 2011
Posts: 119
Thanked 5 Times in 4 Posts
Well buggy drivers is itīs own story, didnīt know it could drop frames without VirtualDub knowing though.
I think however, mine doesnīt, as i got a TimeStamp running on it as a PostProcess, and itīs correct, which it probably wouldnīt be if it dropped frames (if i drop/insert with VirtualDub it is out of sync).

Guess i will have to ask someone with a Webcam to do a VD test for me or something.
Reply With Quote
Reply




Similar Threads
Thread Thread Starter Forum Replies Last Post
Changed frame rate, now have audio sync problems? rand107 Encode, Convert for streaming 1 07-29-2014 08:08 AM
Interlaced video to progressive (double frame rate) metaleonid Edit Video, Audio 23 09-29-2013 09:51 PM
VirtualDub timing options? Frame drops with ATI 600 PCI card? frank_aspen Capture, Record, Transfer 18 01-14-2013 09:19 PM
Editing in VirtualDub is frame-accurate? naripeddi Edit Video, Audio 8 08-16-2012 03:14 AM
Frame rate trouble in DVD Architect Reading Bug Encode, Convert for discs 15 12-31-2009 01:39 PM

Thread Tools



 
All times are GMT -5. The time now is 11:39 AM