Combining videos with different fps

[michn]

Hi,

I'm making an application that records two video pieces from a webcam and then automatically concatenates these videos with a number of predefined videos. Since i use recordings from a webcam I can't guarentee that it has a certain fps and I therefore have a situation where the videos i need to combine have different fps.
I had this working very well using mpeg (simply copying the bytes of the files together into 1 file) but from what i've been able to find out mpeg doesn't support fps below 20 (at least not using ffmpeg encoder). I have therefore tried with mp4 which supports variable frame rate and therefore should support combining videos with different fps. But when i try to combine the videos I've recorded with my web cam with the predefined video pieces using mp4box it doesn't work. I get a file where it combines the videos recorded by the webcam in one video track and the predefined videos in another track.

I use the following command:

mp4box -cat video1.mp4 -cat webcam1.mp4 -cat video2.mp4 -cat webcam2.mp4 -cat video3.mp4 output.mp4

It gives me the following output:

Appending file video1.mp4
No suitable destination track found - creating new one (type vide)
Appending file webcam1.mp4
No suitable destination track found - creating new one (type vide)
Appending file video2.mp4
Appending file webcam2.mp4
Appending file video3.mp4
Saving to output.mp4: 0.500 secs Interleaving

Does anyone have any idea how I can combine these videos into 1 video? It doesn't have to be using mp4box, the only requirement is that it can be used from a commandline (or alternatively has .NET API). I'm open to using other video formats as well as long as I can use varying frame rates.

[oronroi]

Hi,

I face this issue as well.
Any help would be appreciated.

Thanks!

[michn]

I ended up solving my issue in the following way:

My video was already being captured in some Silverlight code by capturing 1 image at a time and then combine it all to one video in the end using ffmpeg. I solved the issue by removing or dublicating some of the frames evenly distributed through the movie so that the final result would have 20 frames per second. Then i combined all these images to 1 video file using ffmpeg. This way i could guarentee that all my video clips had 20 fps and it was no problem combining them. I used mpg format for this btw but im pretty sure it would work with mp4 as well as the fps is the same.

Dunno if this helps you

[oronroi]

Thanks!

[jagabo]

I solved the issue by removing or dublicating some of the frames evenly distributed through the movie so that the final result would have 20 frames per second.

In AviSynth that's a simple "ChangeFPS(20)". VirtualDub does frame rate conversion that way too. If you're making a DVD you can encode as progressive at the native frame rate and apply pulldown flags to any video from 19.98 fps to 29.97 fps.