If you ever downloaded a backup of your Fritz!Box’ “telephony files” (Telefonie-Daten), you may wondered about those .rec files of your voicebox and how to convert them into something more usable. Here is how you can do it:
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/) and other members (https://www.ip-phone-forum.de/threads/laborfirmware-ab-dateien-rec-0-xxx-auf-pc-abspielen.131970/post-858409) for implementing and reversing the audio codec! In detail, the codec uses speex (like the .ogg container format), but without any header. Anything after 0x26 should be ignored to form proper speex encoded audio.
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