Render to avi format using ffmpeg as target and a video bit rate higher than 2000 and Xvid as video codec. If no ffmpeg available as valid target, use png sequence and then import the image sequence to Avidemux(Avidemux has 25 fps by default for image sequence) or Virtualdub.
Any other video editor would be valid if it suits your needs.
Have you defined the path for the saved rendered file? or did you accepted the default one? Some times user doesn’t look where file is.
Does it happen for any kind of target type (png, ffmpeg, gif) or just for one of them?
No, no, not the file extension. I mean the target renderer (ffmpeg, png, yuv420p, gif, jpeg) from the drop down menu.
You can choose some different file extensions for the same target. For example you can render to avi or to mp4 using ffmpeg target. Also there is a Automatic target selector based on file extension but maybe some extensions doesn’t work well.
They are bundled with the Windows binary. It’s an option to install ffmpeg, but the option is to do so by default.
For Windows Vista and Win7, you might want to check where you think you’re saving your file to. Some locations are guarded by Windows (e.g. c:\Program Files (x86)\Synfig\bin or c:) Windows will lie and say it has saved a file there (and through the Synfig file dialog it may even pretend to show it where you think it ought to be), but in fact will save it to a ‘safe’ place - you’ll have to use search to find it through the file manager. Saving to your documents dir or desktop is usually safe.
The other thing to watch out for may be using special characters in the filename.