ffmpeg help... convert mp4 to jpeg array, and back to mp4 - problem!

[SaskVideoMaker]

I am new to ffmpeg, although it is working for the most part.

I have a video, I output it to a jpeg picture array using the following command:

ffmpeg -i M4H08111.MP4 -b 2000 -qscale 1 -qcomp 0 -qblur 0 foo-%03d.jpeg

this seems to provide equal quality to the original video.

then when I recompile the jpegs back into video no matter what I set the frame rate at, the video length is 4 minutes instead of 2 minutes and 30 seconds like the original. I use the following command:

ffmpeg -i foo-%03d.jpeg -r 29.97 -b 8973kb -minrate 8973kb -maxrate 8973kb -bufsize 10000kb foo2.mp4

Does it create additional frames from the source frames to accommodate the fps? Is there a way I can specify how long the video should be? Also I should note that when I play the compiled video in MPlayer it always shows the fps as the value I set in the command line parameter, however the video length is always the same value.

help!

thanks...

[SaskVideoMaker]

looks like I solved my own problem... I used the following command:

ffmpeg -r 30 -i foo-%03d.jpeg -r 30 -b 8973kb -minrate 8973kb -maxrate 8973kb -bufsize 10000kb foo2.mp4

I tried one similar to this using a -r value of 29.97... but it turned out having a video length of almost 2 hours. I don't think that it divides single images properly... so I thought I would just bump it to 30 fps and see what happens... and it worked.

[Gavino]

There's no reason your command shouldn't also work with -r 29.97.

In fact, the second -r is unnecessary - the important thing is to set the input frame rate (otherwise it defaults to 25), which will also become (by default) the output rate. So this should work:
ffmpeg -r 29.97 -i foo-%03d.jpeg -b 8973kb -minrate 8973kb -maxrate 8973kb -bufsize 10000kb foo2.mp4