GAPK Integration¶

GAPK (GSM Audio Pocket Knife) is a FFmpeg like project focused on GSM related codecs (HR/FR/EFR/AMR) and formats. Since the libosmogapk was introduced, it becomes possible to link OsmocomBB against it and use its API for audio processing, i.e. for both voice capture and playback.

Some initial work around this was already done, and has been published in a separate branch (fixeria/audio).

PHY support¶

Both trxcon and VIRT-PHY do forward TCH frames to the higher layers (e.g. mobile) by default, while Calypso-based phones can handle them either within DSP (both regular phone's mic and speaker are involved), or also forward them via L1CTL. The forwarding behaviour can be enabled using L1CTL_TCH_MODE_REQ message and its AUDIO_TX_TRAFFIC_REQ | AUDIO_RX_TRAFFIC_IND flags.