Input:

D:\Users\Shimmy\Music\ConversionTests>ffmpeg -i sample.wmv -vcodec amv -acodec adpcm_ima_amv -r 16 -target sample.a
mv

Output:
......blah blah...........

Could not determine norm (PAL/NTSC/NTSC-Film) for target.
Please prefix target with "pal-", "ntsc-" or "film-",
or set a framerate with "-r xxx".

D:\Users....\>