Dropped Frame Handling

mingshenguni · Post by **mingshenguni** » Sun Aug 20, 2006 9:59 am

When a frame is dropped during video capturing, would a good frame before the dropped frame be inserted into the avi file?

Also in the Video Capture of MediaStuidio Pro 7, there is an option: Exactly match the specified frame rate. If the option is checked, does it mean that if the video capture encountering too many dropped frame, the frame rate would be dynamically reduced? What if at the start of video capture, there is no dropped frame and then sometime during the video capture, another program starts which cause the cpu load to increase and dropped frame then happens. Would the video capture frame rate be automatically reduced at that time if the option is not checked?

I have also tried a non-Ulead video capture program. I captured video for 2 minutes on a pc with heavy cpu load. When I played back the video, it finished playing in 25 seconds with quick motion. If I captured the video using MediaStudio Video Capture at the same condition, the playback would finish in 2 minitues but video playback was very jerky. Does that mean MediaStudio Video Capture and the other program handle dropped frame differently?

heinz-oz · Post by **heinz-oz** » Thu Aug 24, 2006 7:00 am

The idea is to capture video without any dropped frames. If you are dropping frames, there is something wrong or your system cannot handle it. Since capture from digital camcorders to the PC via firewire in DV-AVI is a simple copy of the data on the tape, most half decent PC's these days can handle it with no problem.

Since we know nothing about your set up at all, no help will/can be forthcoming. You will have to provide more detail to get help. Reading this might help you to understand what is required http://phpbb.ulead.com.tw/EN/viewtopic.php?t=8961

mingshenguni · Post by **mingshenguni** » Thu Aug 24, 2006 7:08 am

> The idea is to capture video without any dropped frames.

I have deliberately increased the cpu load while doing video capture. The aims is to study how dropped frames are handled in different programs including Ulead Video Capture. Thanks.

Terry Stetler · Post by **Terry Stetler** » Thu Aug 24, 2006 7:27 am

You'll find that some programs (AVI_IO for analog) duplicate the last frame captured where the drop occurs. Other programs do not.

I prefer not to have this done because then I can feed the footage through DynaPel's MotionPerfect, which will synthesize a P frame from the frames on either side of a drop based on motion vectors. Most often this looks much smoother than a frame copy.

http://www.dynapel.com/index.shtml

Of course heinz-oz is correct: 'tis better to address drop-causing issues before setting about a routine of fixing them after the fact.

mingshenguni · Post by **mingshenguni** » Thu Aug 24, 2006 7:47 am

Many thanks.

If a dropped frame is replaced by the last good frame, is this substitue frame called a blank frame?

VirtualDub can detect dropped frame. Is the dropped frame in this case just a blank frame?

heinz-oz · Post by **heinz-oz** » Thu Aug 24, 2006 8:11 am

frankly, I don't care, sorry. Why would you want to investigate what really happens with dropped frames? It's so easy to avoid them in the first place.

mingshenguni · Post by **mingshenguni** » Thu Aug 24, 2006 8:46 am

Thank you for sharing your emotion. It would be much appreciated if you could share your idea or knowledge. I need to capture several video streams simultaneously and often encounter dropped frames. Cheers

Terry Stetler · Post by **Terry Stetler** » Thu Aug 24, 2006 5:02 pm

Therein lies your problem. While it's possible it's by no means advisable unless you're using multiple machines (duh) or one extremely fast one with a fast RAID array & fat system bus. Since you've not seen fit to enlighten us by filling out your profiles system specs.....

mingshenguni · Post by **mingshenguni** » Thu Aug 24, 2006 11:11 pm

Hi, sorry, I haven't spelled it out clearly. I was not particularly in this instance interested in asking for help on how to reduce dropped frames for my application. I was merely interested in the internals of dropped frames such as the questions I have asked earlier so that I can come up with some solutions myself.

My original question was: If a dropped frame is replaced by the last good frame, is this substitute frame called a blank frame? VirtualDub can detect dropped frame. Is the dropped frame in this case just a blank frame?

Thanks.

Terry Stetler · Post by **Terry Stetler** » Fri Aug 25, 2006 5:41 am

No, it's not a blank frame because it isn't blank. It contains the image in the previous frame when capable software detects a drop and does the substitution. Problem is that in video with any degree of motion this shows as a jitter almost as bad as the one from a total frame drop.

This is why I prefer to keep the drop and have Motion Perfect do a better substitution; a P frame calculated from motion vectors.

Hoe to detect a frame drop? In video with timecode there may be an interruption. Sometimes this will also trip up scene detection, causing scene breaks where one shouldn't be. Another way is to look for a missing field and not a missing whole frame.