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[mod_opus] Fix to allow transcoding between different rates #2832

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[mod_opus] Fix to allow transcoding between different rates #2832

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c7455f5
[core/media] allow transcoding between different rates in Opus
shaunjstokes Oct 14, 2024
ac8b8af
[mod_opus] set RTP interval for RFC 7587 compliance
ticpu Aug 1, 2025
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23 changes: 23 additions & 0 deletions src/mod/codecs/mod_opus/mod_opus.c
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Original file line number Diff line number Diff line change
Expand Up @@ -144,6 +144,7 @@ struct opus_context {
enc_stats_t encoder_stats;
codec_control_state_t control_state;
switch_bool_t recreate_decoder;
uint32_t encoder_samplerate;
};

struct {
Expand Down Expand Up @@ -177,6 +178,11 @@ static switch_bool_t switch_opus_acceptable_rate(int rate)
return SWITCH_TRUE;
}

static inline uint32_t opus_ts_step(uint32_t ptime_ms, uint32_t enc_rate)
{
return (ptime_ms * 48); /* 48 kHz RTP clock rate */
}

static uint32_t switch_opus_encoder_set_audio_bandwidth(OpusEncoder *encoder_object,int enc_samplerate)
{
if (enc_samplerate == 8000) { /* Audio Bandwidth: 0-4000Hz Sampling Rate: 8000Hz */
Expand Down Expand Up @@ -618,6 +624,9 @@ static switch_status_t switch_opus_init(switch_codec_t *codec, switch_codec_flag
return SWITCH_STATUS_GENERR;
}

/* Store encoder sample rate for RTP timestamp scaling */
context->encoder_samplerate = enc_samplerate;

/* https://tools.ietf.org/html/rfc7587 */
if (opus_codec_settings.maxaveragebitrate) {
opus_encoder_ctl(context->encoder_object, OPUS_SET_BITRATE(opus_codec_settings.maxaveragebitrate));
Expand Down Expand Up @@ -680,6 +689,7 @@ static switch_status_t switch_opus_init(switch_codec_t *codec, switch_codec_flag
if (opus_prefs.adjust_bitrate) {
switch_set_flag(codec, SWITCH_CODEC_FLAG_HAS_ADJ_BITRATE);
}

}

if (decoding) {
Expand Down Expand Up @@ -718,6 +728,19 @@ static switch_status_t switch_opus_init(switch_codec_t *codec, switch_codec_flag
}
}

/* Set RTP interval for RFC 7587 compliance */
if (codec->session) {
switch_rtp_t *rtp = switch_core_media_get_rtp_session(codec->session, SWITCH_MEDIA_TYPE_AUDIO);
if (rtp) {
uint32_t ptime_ms = codec->implementation->microseconds_per_packet / 1000;
uint32_t step = opus_ts_step(ptime_ms, codec->implementation->actual_samples_per_second);
switch_rtp_set_interval(rtp, ptime_ms, step);
}
} else {
switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_WARNING,
"Opus codec initialized without session - RTP interval not configured\n");
}

context->codec_settings = opus_codec_settings;
codec->private_info = context;

Expand Down
4 changes: 4 additions & 0 deletions src/switch_core_media.c
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Expand Up @@ -5517,6 +5517,10 @@ SWITCH_DECLARE(uint8_t) switch_core_media_negotiate_sdp(switch_core_session_t *s
uint32_t bit_rate = imp->bits_per_second;
uint32_t codec_rate = imp->samples_per_second;

if (!strcasecmp(map->rm_encoding, "opus")) {
codec_rate = imp->actual_samples_per_second;
}

if (imp->codec_type != SWITCH_CODEC_TYPE_AUDIO) {
continue;
}
Expand Down