how to slow down video framerate ?

[lordsmurf]

I've got two files here.
One is the full 25-minute audio track. It is fine.
The other is the 25 minute video track. It is NOT fine.

The video is too fast,
At about the 15 minute mark, it turns to black screen.
The entire 25 minutes of video was somehow crammed into that 15 minute timeframe, but at a speed faster than 29.97fps.
Now then, the MPEG source file is 29.97.

I obviously need to crop off the black. That will give me the full proper length video. But it will be 25 minutes occupying a 15-minute space.

I'm sure I could figure this out on my own, but I'm willing to hear any ideas, especially if somebody has experience fixing a mess like this.

The sticky part is figuring out how to re-expand the video to fill up the 25-minute timespan. I'm sure frames will be repeated, that's fine. I'm not worried as much about that as I am in getting audio and video back in sync.

[gastorgrab]

I'm not sure i can help but i would like to follow along.

To clarify, is this the state of the file in a multiplexed form, or have the streams been split?

An observation; AviSynth sometimes "runs the video too fast" when you load RealMedia, and then fills the rest of the timeline with black frames. Your solution might be my solution also!

[lordsmurf]

Well, what I'm doing right now is waiting 27 minutes.

The audio and video started out muxed. It was MPEG-1 source. I demuxed it. That left me with these two files. I took Womble and cut off the black end. I opened the video clip in Premiere (must be named .MPG, won't see .M1V) and then told it to expand the clip out to the same time as the WAV audio file (I opened the audio file in SOUNDFORGE and viewed the length in SMPTE). It was converted from MP2 to WAV using Besweet.

The Premiere preview looked fine. In a half hour, I'll see how well it worked out. I'm sure it'll be slightly choppy from expanding the frame rate and making new image data, but that's better than the alternative.

[gastorgrab]

thought #1
I seem to remember something a while back (i think it was on a MAC site), about using a hex editor to alter the header of mpeg files.

thought #2
Possible, you used Womble to demux the file that was already damaged but it was too intelligent. Maybe you need a dumber demuxer.

-------edit------

where exactly is the framrate value stored in a mpeg? i would expect it to be in the header, but it should also be in the video stream alone, and not at all in the audio stream.

[lordsmurf]

I used TMPGENC to demux the file. It was simply a damaged file. Something happened to it before I got it.

RESTREAM can alter MPEG headers.

[gastorgrab]

Here's what i was thinking of;
http://homepage.mac.com/rnc/EditMpegHeaderIFO.html

Does ReStream rely on an existing correct framerate? Is the destination framerate calculated from the starting framerate? What happens when the existing value is garbage?

-----edit--------

i just tried the above method on elem video stream and it seems to work without a hitch, and no re-encoding.

I guess it depends on how much your file is damaged.

[johns0]

Not sure how this will work but load the video into virtualdubmod and change the framerate to 20 fps and frame serve to tmpgenc and encode as 29.97 fps.Might need to adjust the fps in virtualdub.

[adam]

If the video was simply sped up, then you simply need to slow it down. There's no reason to change the number of frames, just return it to its original framerate.

You could do this with avisynth using the assumefps(29.97) command. You could also use VirtualDub. Just set it to full processing mode for video and use the framerate option to set it to 29.97fps. The default settings change framerate via actual speed changes, not via frame duplication/decimation.

If you are going to re-encode this video anyway, then most encoders will let you do such a framerate change. In TMPGenc just set output to 29.97fps and enable the do not framerate conversion filter, for example.

[gastorgrab]

Is he reencoding the file or just trying to restore it?

I guess to ensure the integrity of the final product, he should really reencode.

-------edit----------

From http://www.pcphotovideo.com/favorite.htm

timefix.zip (Download) Here's a little utility to run in a DOS window. Some of us using ReplayTV extracted mpegs found that some of the mpegs have a problem with some headers that cause an mpeg to be say 1 hour long, but when editing it, find it's only 10 minutes or so. We had all kinds of problems with certain programs not reporting the correct length of play time. This created more problems when we attempted to edit those mpegs. This little utility will not alter the actual mpeg but it will "fix" (or attempt to) the incorrect headers. The result is the full mpeg is cut into 2 or more parts. But both parts are now fixed. There NO attempt to make any cuts with regard to GOP structure etc. But I've been using Womble to re-join the fixed mpegs with no problem. I've only had this problem in maybe 1 out of 20 ReplayTV mpegs. I had one that just would NOT be fixed. TMPGenc, Womble and everything else choked on it. I used this little utility and it saved me from throwing out a "one time" record. I'm thinking that you guys with this "post edit audio sync" problem might want to give this a try. Parse your Mpeg with this before you do any editing. Please let me know how it works.

[lordsmurf]

The original framerate is gone. Must re-encode.
The PREMIERE trick worked perfectly.