How to do I convert an animated gif to an mp4 or mv4 on the command line

You can use ffmpeg to do this. There are several examples over on the ffmpeg website.

Here are a few of them:

1. This will create one thumbnail image every minute, named img001.jpg, img002.jpg, img003.jpg, ... (%03d means that ordinal number of each thumbnail image should be formatted using 3 digits)

   $ ffmpeg -i myvideo.avi -f image2 -vf fps=fps=1/60 img%03d.jpg
   

2. This will create one thumbnail image every 10 minutes, named thumb0001.bmp, thumb0002.bmp, thumb0003.bmp, ...

   $ ffmpeg -i test.flv -f image2 -vf fps=fps=1/600 thumb%04d.bmp
   

If you want to make them into a short video you can again enlist the help of ffmpeg. It's discussed on this page of their website.

Here are a few more examples:

1. Here, each image will have a duration of 5 seconds (the inverse of 1/5 frames per second). By telling FFmpeg to set the input file's FPS option (frames per second) to some very low value, we made FFmpeg duplicate frames at the output and thus we achieved to display each image for some time on screen:

   $ ffmpeg -f image2 -r 1/5 -i img%03d.png -c:v libx264 -r 30 out.mp4
   

2. If you don't have images numbered and ordered in series (img001.jpg, img002.jpg, img003.jpg) but rather random bunch of images, ffmpeg also supports bash-style globbing (* represents any number of any characters):

   $ ffmpeg -f image2 -r 1 -pattern_type glob -i '*.jpg' -c:v libx264 out.mp4
   

or for png images:

    $ ffmpeg -f image2 -r 1 -pattern_type glob -i '*.png' -c:v libx264 out.mp4

To make the resulting video into an animated gif you could use the steps outlined int his SO Q&A titled: How to generate gif from avi using ffmpeg?:

$ ffmpeg -i video.avi -t 10 out%02d.gif

then:

$ gifsicle --delay=10 --loop *.gif > anim.gif

Here's the link to the tool gifsicle.

You don't mention in your post if you've tried the most basic command that should accomplish this:

ffmpeg -i input.swf output.gif

Assuming that works there are going to be quality problems with it, because GIF is a 256-color format. (Imgur recently extended the file format for GIFV which uses WebM video, but that's a separate topic)

If that didn't work, it's because you don't have a SWF decoder or a GIF encoder. You can run this command to see what codecs/formats are supported by your version of FFMpeg:

ffmpeg -formats

The output of that is pretty verbose (it will list everything) and you can use grep to cut it down for you:

ffmpeg -formats | grep -i GIF
ffmpeg -formats | grep -i SWF

For me I get this:

 DE gif             GIF Animation
  E avm2            SWF (ShockWave Flash) (AVM2)
 DE swf             SWF (ShockWave Flash)

This shows that my version of FFMpeg supports decoding and encoding GIF and SWF.

You may also want to test converting it to an AVI before converting it to GIF, to see the quality before any GIF problems:

ffmpeg -i input.swf -sameq output.avi

It may get mad about trying to use the -sameq flag because SWF doesn't have a "quality". You could also try -b:v 900k to set the video bitrate to pretty high.

Update

The source you linked to can easily be compiled on any Linux system that has GCC and the "zlib" library (almost everything has that) Here is how I compiled it:

sudo apt-get install build-essential zlib-dev
wget -o main.c "http://svn.perian.org/ffmpeg/tools/cws2fws.c"
gcc main.c -lz

You can now run the tool to convert like this:

./a.out input.swf decompressed.swf

Cheers