Or
nFname="${base}.mp4"

Using brackets you can mix variables and text and create something like this:
newName="${oldname}-bkp-${filedate}.${extension}.old"

Mauro
http://mauro.limeiratem.com - registered Linux User: 294521
Scripture is both history, and a love letter from God.

2017-01-08 13:21 GMT-02:00 William Park via talk <talk@gtalug.org>:
On the topic of quotes, see my in-line comments...

On Sun, Jan 08, 2017 at 05:57:40AM -0500, Stephen via talk wrote:
> On 2017-01-07 07:25 PM, Stephen via talk wrote:
> > #!/bin/bash
> > # Usage: convert file to mp4
> > shopt -s nullglob
> > ext='.mp4'
> > for f in *.mkv
> > do
> >    base=$(basename $f .mkv)

Should be
    base=$(basename "$f" .mkv)

> >    nFname=$base".mp4"

    nFname="$base".mp4

> >    echo $nFname
> >    avconv "-i $f -c:v libx264 -c:a copy $nFname"

    avconv -i "$f" -c:v libx264 -c:a copy "$nFname"

> > done
>
>
> Thank you for the replies. Simply removing the quotes did the trick! :)