[Ffmpeg-devel] Error when reading asf file: "Error while opening file"

[development at imberg.de]

What I want to do:
Read an asf file which ist created by an php script which reads an asf
stream from an internet camera.

I tried to read the asf file and convert it to a single jpg picture by
entering this:
ffmpeg -i Test.asf -y -f mjpeg Test.jpg
Then this error occurs: "Test.asf: Error while opening file"

When I create the asf file with the software delivered with the WebCam
the call works fine and I get the Test.jpg picture.

When I play the php-script-created Test.asf file with e.g. the windows
media player or other player tools is also works fine.

So has anybody an idea what is wrong or different to this asf file or
why ffmpeg behaves like it does? ( Error while opening file)

Best regards
  Ralf