Removing every other frame from an AVI...

[filmjax]

I apologize in advance if this is a ridiculously stupid question...

In the early 90s I had a video camera that had this wonderful feature. If you were filming and moved from the indoors to the outdoors, for the next four hours or so, anything the camera recorded was completely garbled.

Anyway, I have a lot of footage on tape from that camera, and I've noticed through my PC editing and capturing programs that its only every other frame of video that's garbled. The other alternate frames look perfectly fine.

I'm not expecting much if this can be done, but is there a way to eliminate every other frame in a file? I know quality will still be poor and the audio won't sound right, but I'd like some usuable images from what I though was once lost forever. Is this possible?

[Sartori]

In Virtual Dub , in the Video menu , go down 2 items to Frame Rate - this opens the Frame Rate Control window . This window is split into 3 sections , the middle one is Frame Rate Decimation - try the Decimate Every Other Frame (decimate by 2) option . It does say on the side that framerate decimation doesnt affect sync . If this works as it should , it`ll either leave you with all good or all bad frames , if bad then delete the first frame to sort that out .

I tried it out on a 4 second / 100 frame (25fps PAL) and this function reduced it to 4 second / 50 frames @ 12.5fps avi .

A couple of points though :
1.This is all theory , because I`d need your file to try it out but it should work.
2.If you drop one frame or more within the captured avi , the sequence will be reversed at that point , so you need to manually drop one more frame at those points to correct this . Vdub has a function to jump you to where a frame was dropped , er I think thats what it does anyway ( in the Edit menu )
3.if it does work and you want to convert the avi to an mpg - I just loaded the 12.5fps avi into tmpgenc and it coughed it out as a 25fps 4sec mpg . I`m assuming its either padding the datastream or its magic or something .
4.obviously you can also add filters etc etc and frameserve it



I hope this works for you .Please IM to tell me if it worked for you .


Rob

[mmasw]

I could be wrong, but I don't believe you can decimate within vdub without re-compressing the video....resulting in quality loss.

[puertorican138]

I could be wrong, but I don't believe you can decimate within vdub without re-compressing the video....resulting in quality loss.

You don't have to re-encode when you decimate the frames in VirtualDub. :P

[mmasw]

"You don't have to re-encode when you decimate the frames in VirtualDub"

true....but I've tried it a few times and the video is always royally screwed up afterwards.

But that was with compressed video like DivX or VP3

still, I'd be curious if decimation without recompression yields functional video

(I wonder if keyframe interval is a factor)

[Sartori]

"You don't have to re-encode when you decimate the frames in VirtualDub"

true....but I've tried it a few times and the video is always royally screwed up afterwards.

But that was with compressed video like DivX or VP3

still, I'd be curious if decimation without recompression yields functional video

(I wonder if keyframe interval is a factor)

When compressing with Divx and decimating it only went pear shaped on me when I changed the sound to anything other than 44100khz , then it went bonkers - hamster voices and 2x video speed etc .
I`ve made quite a few videos with the frame rate reduced to 20/21/22fps in order to allow the bitrate to produce better quality frames , BUT the Max Headroom clunkiness does creep in a bit at lower rates .

Some Real Media Videos I had were 15/20fps which after converting to avi , easily converted to mpeg1 and play fine in my dvd player .

I didn`t think avi had keyframe intervals as far as vdub was concerned because it shows all frames - even if it does ... all my videos are fine .

To make sure mine synced ok , I ripped the wav with vdub , then processed/decimated the avi , then used the decimated avi and the ripped wav as audio and video inputs in Tmpgenc .

The purpose of it ? To encode as much to a cd , so I could have as much on one disc as possible and take it into work , to watch Tv episodes in work and get paid for it

[dphirschler]

Use AVIsynth and the "selectevery" command. Very easy.


Darryl