libtwamr encoder: always emit frame->mode = mode; In the original implementation of amr_encode_frame(), the 'mode' member of the output struct was set to 0xFF if the output frame type is TX_NO_DATA. This design was made to mimic the mode field (16-bit word) being set to 0xFFFF (or -1) in 3GPP test sequence format - but nothing actually depends on this struct member being set in any way, and amr_frame_to_tseq() generates the needed 0xFFFF on its own, based on frame->type being equal to TX_NO_DATA. It is simpler and more efficient to always set frame->mode to the actual encoding mode in amr_encode_frame(), and this new behavior has already been documented in doc/AMR-library-API description in anticipation of the present change.

/*
 * The function implemented in this module groks the first octet of
 * an RFC 4867 payload and tells the calling application how many more
 * bytes need to be read, or if the frame type is invalid.
 */

#include <stdint.h>
#include "tw_amr.h"

static const uint8_t extra_bytes_per_ft[9] =
		{12, 13, 15, 17, 19, 20, 26, 31, 5};

int amr_ietf_grok_first_octet(uint8_t fo)
{
	uint8_t ft;

	ft = (fo & 0x78) >> 3;
	if (ft == AMR_FT_NODATA)
		return 0;
	if (ft > MRDTX)
		return -1;
	return extra_bytes_per_ft[ft];
}