Technical digital camera question...

Off-topic
1

My camera takes videos at 25 frames per second but it takes them in groups of three identical frames. So it seems to me that 2/3 of the frames that the camera takes are useless and the frame rate is really about 9 frames per second. Why does it do this?

I wish I had a camera like the one Ryan’s been using that actually does take 25 frames per second. The videos look so much smoother.

Thanks,
Andrew

2

That is weird. Maybe they are doing that for some technical or compatibility reason for doing it. MPEG can encode at less than 25 or 30 fps. It makes the MPEG file less standard, but it can be done and MPEG supports it.

My camera (Casio QV-4000) will record video at 15 fps (real 15 fps, no duplicated frames) in AVI format, but does not record audio. It does OK for a still camera.

You can use VirtualDub to get rid of the duplicated frames if you convert the video to AVI format. Go to Video >> Frame Rate… and tell it to process every third frame.

3

Thanks John, I knew you’d have an answer for this one :). Wouldn’t processing every third frame change the speed that the video plays at? If you keep the original frame rate that it plays the video with? Would I just have to halve it?

Thanks,
Andrew

4

When VirtualDub processes every other or every third frame it keeps the audio and video in sync. The video will not run faster or slower. In your case the fps will change from 25 to 8.333 so that if the original video was 5 seconds the one with every third frame processed will also be 5 seconds long.

If you’re going to edit and convert one of the MPEG videos with duplicated frames into an AVI, you should process only every third frame so that the AVI will be smaller (fewer frames to encode). I think some codecs might be smart enough to compress the duplicated frames efficiently, but I think it would still add to the overall file size with no visible benefit and cause extra work for the encoder/decoder.

5

Using repeated frames could be just a way so they can write “25 Frames Per Second!” on the box. When I got my webcam it said “640x480 resolution; 25fps”… it missed out the vital “but not at the same time” part…

Phil

6

I suppose you should first find out if your camera is working properly. There should be some sort of technical info page on the Web (not that this means there necessarily isone). Otherwise, try Steve’s Digicams Web site or others for discussions on the video from your camera. You may find that your camera has something wrong with it.