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doc/AMR-library-API: document AMR-EFR hybrid decoder
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 19 May 2024 22:22:40 +0000
parents 936a08cc73ce
children 332397bc80aa
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478:936a08cc73ce 479:616b7ba1135b
384 384
385 int amr_txtype_to_rxtype(enum TXFrameType tx_type, enum RXFrameType *rx_type); 385 int amr_txtype_to_rxtype(enum TXFrameType tx_type, enum RXFrameType *rx_type);
386 386
387 The return value is 0 if tx_type is valid and *rx_type has been filled 387 The return value is 0 if tx_type is valid and *rx_type has been filled
388 accordingly, or -1 if tx_type is invalid. 388 accordingly, or -1 if tx_type is invalid.
389
390 AMR-EFR hybrid decoder
391 ======================
392
393 To use libtwamr as an AMR-EFR hybrid decoder, follow these steps:
394
395 * Turn the input frame from EFR RTP format into array-of-parameters form with
396 libgsmefr function EFR_frame2params(), writing the output into the param[]
397 array in struct amr_param_frame.
398
399 * Set 'type' in the struct to RX_SPEECH_GOOD for good frames, RX_SPEECH_BAD for
400 BFI with payload bits present, or RX_NO_DATA for BFI without payload.
401
402 * Set 'mode' to 0x87 always, indicating a variation of MR122 with EFR DHF
403 instead of the different native MR122 DHF.
404
405 * Call amr_decode_frame() with this input.
406
407 Fundamental limitation: the AMR decoder in libtwamr, derived from 3GPP AMR
408 reference source and only minimally extended to support EFR DHF, does not
409 support EFR SID frames. Therefore, the option of AMR-EFR hybrid emulation via
410 libtwamr is limited to lab experiments where the input to the decoder can be
411 ensured to be SID-free, and is not suitable for production use. See
412 AMR-EFR-philosophy article for more information.