Fritz!Box uses an exotic format for saving audio files internally (voicebox recordings and announcement files). Even VLC is not able to play it. We can, however, quickly convert it to standard wav files to be able to play the file and archive it.
For this, we use speexdec-fb which is a fork of speexdec with the necessary modifications for supporting audio files encoded by the Fritz!Box. The FritzBox Speex Codec does not use a header and is custom to the Fritz!Box. Thank you to “J.C.” of this Forum Thread (https://www.ip-phone-forum.de/threads/fritz-box-anrufbeantworter-encoder-decoder.156186/) for implementing and reversing the audio codec!
First, we clone the repository to our local system using git clone or download it as an zip from Github’s website:
git clone https://github.com/msilvoso/speexdec-fb
Inside the speexdec-fb folder, we can now compile the program using:
./configure && make
Afterwards, we find the binaries in the src folder.
To convert a recording we can use the speexdec binary:
./speexdec rec.0.111 outputfile.wav