mirror of https://gerrit.osmocom.org/gapk
92 lines
2.7 KiB
C
92 lines
2.7 KiB
C
/* EFR RTP Payload according to RFC3551. Only one codec frame per RTP */
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/* (C) 2017 by Harald Welte <laforge@gnumonks.org> */
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/*
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* This file is part of gapk (GSM Audio Pocket Knife).
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*
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* gapk is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* gapk is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with gapk. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdint.h>
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#include <assert.h>
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#include <osmocom/codec/codec.h>
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#include <osmocom/gapk/codecs.h>
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#include <osmocom/gapk/formats.h>
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#include <osmocom/gapk/utils.h>
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#define EFR_LEN 31
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#define EFR_MAGIC 0xc
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/* EFR encoding starts with 0xc, if all other bits are 0 the packet is probably damaged */
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static const uint8_t DAMAGED_PACKET[EFR_LEN] = {
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0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
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};
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/* EFR SID frame is according to TS 101 318 5.3.2 */
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static const uint8_t SILENCE[EFR_LEN] = {
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0xcf, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xe0, 0x00, 0x00,
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0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
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};
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/* conversion function: RTP payload -> canonical format */
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static int
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rtp_efr_from_canon(uint8_t *dst, const uint8_t *src, unsigned int src_len)
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{
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int i;
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/* according to RFC3551 4.5.9 */
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assert(src_len == EFR_CANON_LEN);
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dst[0] = (EFR_MAGIC << 4) | (src[0] >> 4);
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for (i=1; i<EFR_LEN; i++)
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dst[i] = (src[i-1] << 4) | (src[i] >> 4);
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return EFR_LEN;
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}
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/* conversion function: canonical format -> RTP payload */
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static int
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rtp_efr_to_canon(uint8_t *dst, const uint8_t *src, unsigned int src_len)
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{
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int i;
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/* broken RTP frames may be short; substitute empty frame */
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if (src_len != EFR_LEN) {
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memset(dst, 0, EFR_CANON_LEN);
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return EFR_CANON_LEN;
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}
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if (!memcmp(DAMAGED_PACKET, src, EFR_LEN))
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src = SILENCE;
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for (i=0; i<(EFR_LEN-1); i++)
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dst[i] = (src[i] << 4) | (src[i+1] >> 4);
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dst[EFR_LEN-1] = src[EFR_LEN-1] << 4;
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return EFR_CANON_LEN;
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}
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const struct osmo_gapk_format_desc fmt_rtp_efr = {
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.type = FMT_RTP_EFR,
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.codec_type = CODEC_EFR,
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.name = "rtp-efr",
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.description = "RTP payload for EFR according to RFC3551",
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.frame_len = EFR_LEN,
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.conv_from_canon = rtp_efr_from_canon,
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.conv_to_canon = rtp_efr_to_canon,
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};
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