I'm new to animation and I'm having rendering issues

I just downloaded Synfig the other day, and I finished my first project.
I’m trying to render to a mp4 using ffmpeg, but when I try to start the render, the command prompt fills with warnings and the render doesn’t happen.
I attached a screen shot of the warnings. What’s going on? More importantly, how do I fix it?

Pay no attention to the warnings, those are always generated (ie. they need to be cleaned at some point).

The important bit is this line:

frame=  323 fps=0.7 q=31 size=     918kB time=00:00:10.76 bitrate= 698.4kbits/

That is the output from the ffmpeg encoder.

It will probably take a LONG time to finish encoding your animation, since it is working at 0.7 frames per second (slower than real time!!!). You can allow the encoder to continue running until it finishes.

Or maybe try adjusting the parameter for ffmpeg (try different codec or bitrate) or rendering with smaller resolution to speed up the encoding a bit.