[FFmpeg-user] Aspect ratio preservation in WMV

[Paul-Antoine Arras]

Hello,

I'm trying to convert the sound of a video from WMA to MP3. To do so, I 
use the following command line:

    ffmpeg -i input.wmv -acodec libmp3lame -aq 4 -vcodec copy output.wmv

The sound is converted correctly but the aspect ratio (AR) becomes 4:3 
instead of 16:9. Then I've tried to force the AR with:

    -aspect 16:9

without success.

Why does ffmpeg modify the AR while all it has to do in this case is a 
simple copy of the video part? How to make it preserve the original AR 
(16:9)?

Thanks in advance for your help.

-- 
Paul-Antoine ARRAS