Render w/ ffmpeg makes empty files

When i do > file render and use ffmpeg it seems to render (some time with 100 cpu load) then the video file made is 0 bytes

render to gif works ok
ffmpeg works ok outside synfig ( movies conversion etc )

synfig 0.62.00 arch linux

Can you paste the terminal output when you render using ffmpeg?
You can run synfigstudio from a terminal to see the output.

lots of this line for the entire time it is rendering

synfig(2263) [04:58:29 PM] warning: Broken Pipe...

Do you have ffmpeg installed?

Yep. and it works in all other applications

what looks weird to me - when synfig renders with ffmpeg it does take 100 cpu load for some time. doesnt it mean that ffmpeg actually is doing some work ? (and then discarding it)

We are about to release a new version. If you wait two weeks you can test if the problem persists using the universal package we provide for synfig and synfigstudio.
Also ffmpeg functionality has changed in the last release to pass the codec and bitrate to the renderer.