Latest official FFmpeg release provided by automatic installation in AVD Preferences is not support Windows XP and some another 32-bit systems anymore.
You can use old version of FFmpeg attached to this article or download one of compatible to your system FFmpeg converters at official site here:
Yo need to save it to any folder (or to your Firefox browser profile folder) and select path with Browse button at the bottom of AVD Toolbar Preferences window.
In this case just select OK after you browse to FFmpeg, don't select Install.
More detailed information about converter you can find at our Help Center here: https://support.ant.com/hc/en-us/articles/115000135526-Why-do-I-need-to-install-video-converter