1/**********
2This library is free software; you can redistribute it and/or modify it under
3the terms of the GNU Lesser General Public License as published by the
4Free Software Foundation; either version 3 of the License, or (at your
5option) any later version. (See <http://www.gnu.org/copyleft/lesser.html>.)
6
7This library is distributed in the hope that it will be useful, but WITHOUT
8ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
9FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
10more details.
11
12You should have received a copy of the GNU Lesser General Public License
13along with this library; if not, write to the Free Software Foundation, Inc.,
1451 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
15**********/
16// "liveMedia"
17// Copyright (c) 1996-2020 Live Networks, Inc. All rights reserved.
18// RTP sink for AC3 audio
19// Implementation
20
21#include "AC3AudioRTPSink.hh"
22
23AC3AudioRTPSink::AC3AudioRTPSink(UsageEnvironment& env, Groupsock* RTPgs,
24 u_int8_t rtpPayloadFormat,
25 u_int32_t rtpTimestampFrequency)
26 : AudioRTPSink(env, RTPgs, rtpPayloadFormat,
27 rtpTimestampFrequency, "AC3"),
28 fTotNumFragmentsUsed(0) {
29}
30
31AC3AudioRTPSink::~AC3AudioRTPSink() {
32}
33
34AC3AudioRTPSink*
35AC3AudioRTPSink::createNew(UsageEnvironment& env, Groupsock* RTPgs,
36 u_int8_t rtpPayloadFormat,
37 u_int32_t rtpTimestampFrequency) {
38 return new AC3AudioRTPSink(env, RTPgs,
39 rtpPayloadFormat, rtpTimestampFrequency);
40}
41
42Boolean AC3AudioRTPSink
43::frameCanAppearAfterPacketStart(unsigned char const* /*frameStart*/,
44 unsigned /*numBytesInFrame*/) const {
45 // (For now) allow at most 1 frame in a single packet:
46 return False;
47}
48
49void AC3AudioRTPSink
50::doSpecialFrameHandling(unsigned fragmentationOffset,
51 unsigned char* frameStart,
52 unsigned numBytesInFrame,
53 struct timeval framePresentationTime,
54 unsigned numRemainingBytes) {
55 // Set the 2-byte "payload header", as defined in RFC 4184.
56 unsigned char headers[2];
57
58 Boolean isFragment = numRemainingBytes > 0 || fragmentationOffset > 0;
59 if (!isFragment) {
60 headers[0] = 0; // One or more complete frames
61 headers[1] = 1; // because we (for now) allow at most 1 frame per packet
62 } else {
63 if (fragmentationOffset > 0) {
64 headers[0] = 3; // Fragment of frame other than initial fragment
65 } else {
66 // An initial fragment of the frame
67 unsigned const totalFrameSize = fragmentationOffset + numBytesInFrame + numRemainingBytes;
68 unsigned const fiveEighthsPoint = totalFrameSize/2 + totalFrameSize/8;
69 headers[0] = numBytesInFrame >= fiveEighthsPoint ? 1 : 2;
70
71 // Because this outgoing packet will be full (because it's an initial fragment), we can compute how many total
72 // fragments (and thus packets) will make up the complete AC-3 frame:
73 fTotNumFragmentsUsed = (totalFrameSize + (numBytesInFrame-1))/numBytesInFrame;
74 }
75
76 headers[1] = fTotNumFragmentsUsed;
77 }
78
79 setSpecialHeaderBytes(headers, sizeof headers);
80
81 if (numRemainingBytes == 0) {
82 // This packet contains the last (or only) fragment of the frame.
83 // Set the RTP 'M' ('marker') bit:
84 setMarkerBit();
85 }
86
87 // Important: Also call our base class's doSpecialFrameHandling(),
88 // to set the packet's timestamp:
89 MultiFramedRTPSink::doSpecialFrameHandling(fragmentationOffset,
90 frameStart, numBytesInFrame,
91 framePresentationTime,
92 numRemainingBytes);
93}
94
95unsigned AC3AudioRTPSink::specialHeaderSize() const {
96 return 2;
97}
98