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If i understood it correctly, the received stream gets decoded and reencoded before saving it.
Wouldn't it be better to save stream as it is (i.e. without any reencoding, but as it comes from DAB device)? in that case it saves CPU from additional processing (decoding/encoding), that can be important especially for older devices (with weak CPUs). E.g. in car headunits there are several apps running simultaneously with DAB receiver app in background, and so DAB receiver app won't get full CPU for decoding/encoding/decoding process.

Audio from AAC services with a single audio channel (mono) is scrambled and "micky-moused", which is testable in Germany with "hr-info".

The problem is in TimeshiftPlayerAacAu and its derived classes. They are using android.media.AudioFormat constants assigned to mAudioTrackChannelConfig.

However, this variable is then used with pcmAudioData in the respective AudioTrackSink class which expects the plain number of channels. Since the AudioFormat constants are flags with values unrelated to the number of channels, mono streams get 4 channels and stereo streams get 12. The latter seems to be working by chance, but the former does not.

Using instead a variable like mAudioTrackNumChannels with the plain number of channels (1 = mono, 2 = stereo) solves the problem. AudioFormat is not required anywhere.