1 /*
2  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
3  *
4  *  Use of this source code is governed by a BSD-style license
5  *  that can be found in the LICENSE file in the root of the source
6  *  tree. An additional intellectual property rights grant can be found
7  *  in the file PATENTS.  All contributing project authors may
8  *  be found in the AUTHORS file in the root of the source tree.
9  */
10 
11 #include "modules/audio_coding/neteq/timestamp_scaler.h"
12 
13 #include "api/audio_codecs/audio_format.h"
14 #include "modules/audio_coding/neteq/decoder_database.h"
15 #include "rtc_base/checks.h"
16 
17 namespace webrtc {
18 
Reset()19 void TimestampScaler::Reset() {
20   first_packet_received_ = false;
21 }
22 
ToInternal(Packet * packet)23 void TimestampScaler::ToInternal(Packet* packet) {
24   if (!packet) {
25     return;
26   }
27   packet->timestamp = ToInternal(packet->timestamp, packet->payload_type);
28 }
29 
ToInternal(PacketList * packet_list)30 void TimestampScaler::ToInternal(PacketList* packet_list) {
31   PacketList::iterator it;
32   for (it = packet_list->begin(); it != packet_list->end(); ++it) {
33     ToInternal(&(*it));
34   }
35 }
36 
ToInternal(uint32_t external_timestamp,uint8_t rtp_payload_type)37 uint32_t TimestampScaler::ToInternal(uint32_t external_timestamp,
38                                      uint8_t rtp_payload_type) {
39   const DecoderDatabase::DecoderInfo* info =
40       decoder_database_.GetDecoderInfo(rtp_payload_type);
41   if (!info) {
42     // Payload type is unknown. Do not scale.
43     return external_timestamp;
44   }
45   if (!(info->IsComfortNoise() || info->IsDtmf())) {
46     // Do not change the timestamp scaling settings for DTMF or CNG.
47     numerator_ = info->SampleRateHz();
48     if (info->GetFormat().clockrate_hz == 0) {
49       // If the clockrate is invalid (i.e. with an old-style external codec)
50       // we cannot do any timestamp scaling.
51       denominator_ = numerator_;
52     } else {
53       denominator_ = info->GetFormat().clockrate_hz;
54     }
55   }
56   if (numerator_ != denominator_) {
57     // We have a scale factor != 1.
58     if (!first_packet_received_) {
59       external_ref_ = external_timestamp;
60       internal_ref_ = external_timestamp;
61       first_packet_received_ = true;
62     }
63     const int64_t external_diff = int64_t{external_timestamp} - external_ref_;
64     RTC_DCHECK_GT(denominator_, 0);
65     external_ref_ = external_timestamp;
66     internal_ref_ += (external_diff * numerator_) / denominator_;
67     return internal_ref_;
68   } else {
69     // No scaling.
70     return external_timestamp;
71   }
72 }
73 
ToExternal(uint32_t internal_timestamp) const74 uint32_t TimestampScaler::ToExternal(uint32_t internal_timestamp) const {
75   if (!first_packet_received_ || (numerator_ == denominator_)) {
76     // Not initialized, or scale factor is 1.
77     return internal_timestamp;
78   } else {
79     const int64_t internal_diff = int64_t{internal_timestamp} - internal_ref_;
80     RTC_DCHECK_GT(numerator_, 0);
81     // Do not update references in this method.
82     // Switch |denominator_| and |numerator_| to convert the other way.
83     return external_ref_ + (internal_diff * denominator_) / numerator_;
84   }
85 }
86 
87 }  // namespace webrtc
88