[FFmpeg-user] Converting mkv to mp3 failures

[JD]

I just wanted to point out that 99% of files I download
as mkv, and then try to convert them to mp3 with the command:

ffmpeg -i somefile.mkv -vn -c:a libmp3lame -ab 320k -ac 2 -y somefile.mp3

fail to convert, with huge amount of error messages output.

PS: Using ffmpeg version 3.0.2-static

The conversion to mkv is done by youtube-dl automatically.

So, is youtube-dl the culprit by creating bad mkv output?

Would love to hear how I can make this work.