how do I config mediatomb to transcode mkv files in place?

[jenia]

Hello:

I want to transcode mkv files to mp4 files in place. I read and followed
the examples on mediatomb's website.

My config doesn't work properly though.
Here it is:

  ...
  <transcode mimetype="video/mkv" using="vlcmpeg"/>
  ...

  <profile name="vlcmpeg" enabled="yes" type="external">
    <mimetype>video/mp4</mimetype>
    <accept-url>yes</accept-url>
    <first-resource>yes</first-resource>
    <hide-original-resource>yes</hide-original-resource>
    <accept-ogg-theora>yes</accept-ogg-theora>
    <agent command="ffmpeg" arguments="-i %in -vcodec copy -acodec copy %out"/>
    <buffer size="14400000" chunk-size="512000" fill-size="120000"/>
  </profile>

At first it was transcoding to the /tmp dir, now it stopped transcoding
altogether for some reason.

Maybe someone can help? So again, I want to transcode mkv files to mp4
files in place.

Thanks.
jenia

P.S. By "in place", I mean for the original, unsupported, file to be hidden
and the transcoded file shown in it's place.