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 MPEG video (RFC 2250)
19// Implementation
20
21#include "MPEG1or2VideoRTPSink.hh"
22#include "MPEG1or2VideoStreamFramer.hh"
23
24MPEG1or2VideoRTPSink::MPEG1or2VideoRTPSink(UsageEnvironment& env, Groupsock* RTPgs)
25 : VideoRTPSink(env, RTPgs, 32, 90000, "MPV") {
26 fPictureState.temporal_reference = 0;
27 fPictureState.picture_coding_type = fPictureState.vector_code_bits = 0;
28}
29
30MPEG1or2VideoRTPSink::~MPEG1or2VideoRTPSink() {
31}
32
33MPEG1or2VideoRTPSink*
34MPEG1or2VideoRTPSink::createNew(UsageEnvironment& env, Groupsock* RTPgs) {
35 return new MPEG1or2VideoRTPSink(env, RTPgs);
36}
37
38Boolean MPEG1or2VideoRTPSink::sourceIsCompatibleWithUs(MediaSource& source) {
39 // Our source must be an appropriate framer:
40 return source.isMPEG1or2VideoStreamFramer();
41}
42
43Boolean MPEG1or2VideoRTPSink::allowFragmentationAfterStart() const {
44 return True;
45}
46
47Boolean MPEG1or2VideoRTPSink
48::frameCanAppearAfterPacketStart(unsigned char const* frameStart,
49 unsigned numBytesInFrame) const {
50 // A 'frame' (which in this context can mean a header or a slice as well as a
51 // complete picture) can appear at other than the first position in a packet
52 // in all situations, EXCEPT when it follows the end of (i.e., the last slice
53 // of) a picture. I.e., the headers at the beginning of a picture must
54 // appear at the start of a RTP packet.
55 if (!fPreviousFrameWasSlice) return True;
56
57 // A slice is already packed into this packet. We allow this new 'frame'
58 // to be packed after it, provided that it is also a slice:
59 return numBytesInFrame >= 4
60 && frameStart[0] == 0 && frameStart[1] == 0 && frameStart[2] == 1
61 && frameStart[3] >= 1 && frameStart[3] <= 0xAF;
62}
63
64#define VIDEO_SEQUENCE_HEADER_START_CODE 0x000001B3
65#define PICTURE_START_CODE 0x00000100
66
67void MPEG1or2VideoRTPSink
68::doSpecialFrameHandling(unsigned fragmentationOffset,
69 unsigned char* frameStart,
70 unsigned numBytesInFrame,
71 struct timeval framePresentationTime,
72 unsigned numRemainingBytes) {
73 Boolean thisFrameIsASlice = False; // until we learn otherwise
74 if (isFirstFrameInPacket()) {
75 fSequenceHeaderPresent = fPacketBeginsSlice = fPacketEndsSlice = False;
76 }
77
78 if (fragmentationOffset == 0) {
79 // Begin by inspecting the 4-byte code at the start of the frame:
80 if (numBytesInFrame < 4) return; // shouldn't happen
81 unsigned startCode = (frameStart[0]<<24) | (frameStart[1]<<16)
82 | (frameStart[2]<<8) | frameStart[3];
83
84 if (startCode == VIDEO_SEQUENCE_HEADER_START_CODE) {
85 // This is a video sequence header
86 fSequenceHeaderPresent = True;
87 } else if (startCode == PICTURE_START_CODE) {
88 // This is a picture header
89
90 // Record the parameters of this picture:
91 if (numBytesInFrame < 8) return; // shouldn't happen
92 unsigned next4Bytes = (frameStart[4]<<24) | (frameStart[5]<<16)
93 | (frameStart[6]<<8) | frameStart[7];
94 unsigned char byte8 = numBytesInFrame == 8 ? 0 : frameStart[8];
95
96 fPictureState.temporal_reference = (next4Bytes&0xFFC00000)>>(32-10);
97 fPictureState.picture_coding_type = (next4Bytes&0x00380000)>>(32-(10+3));
98
99 unsigned char FBV, BFC, FFV, FFC;
100 FBV = BFC = FFV = FFC = 0;
101 switch (fPictureState.picture_coding_type) {
102 case 3:
103 FBV = (byte8&0x40)>>6;
104 BFC = (byte8&0x38)>>3;
105 // fall through to:
106 case 2:
107 FFV = (next4Bytes&0x00000004)>>2;
108 FFC = ((next4Bytes&0x00000003)<<1) | ((byte8&0x80)>>7);
109 }
110
111 fPictureState.vector_code_bits = (FBV<<7) | (BFC<<4) | (FFV<<3) | FFC;
112 } else if ((startCode&0xFFFFFF00) == 0x00000100) {
113 unsigned char lastCodeByte = startCode&0xFF;
114
115 if (lastCodeByte <= 0xAF) {
116 // This is (the start of) a slice
117 thisFrameIsASlice = True;
118 } else {
119 // This is probably a GOP header; we don't do anything with this
120 }
121 } else {
122 // The first 4 bytes aren't a code that we recognize.
123 envir() << "Warning: MPEG1or2VideoRTPSink::doSpecialFrameHandling saw strange first 4 bytes "
124 << (void*)startCode << ", but we're not a fragment\n";
125 }
126 } else {
127 // We're a fragment (other than the first) of a slice.
128 thisFrameIsASlice = True;
129 }
130
131 if (thisFrameIsASlice) {
132 // This packet begins a slice iff there's no fragmentation offset:
133 fPacketBeginsSlice = (fragmentationOffset == 0);
134
135 // This packet also ends a slice iff there are no fragments remaining:
136 fPacketEndsSlice = (numRemainingBytes == 0);
137 }
138
139 // Set the video-specific header based on the parameters that we've seen.
140 // Note that this may get done more than once, if several frames appear
141 // in the packet. That's OK, because this situation happens infrequently,
142 // and we want the video-specific header to reflect the most up-to-date
143 // information (in particular, from a Picture Header) anyway.
144 unsigned videoSpecificHeader =
145 // T == 0
146 (fPictureState.temporal_reference<<16) |
147 // AN == N == 0
148 (fSequenceHeaderPresent<<13) |
149 (fPacketBeginsSlice<<12) |
150 (fPacketEndsSlice<<11) |
151 (fPictureState.picture_coding_type<<8) |
152 fPictureState.vector_code_bits;
153 setSpecialHeaderWord(videoSpecificHeader);
154
155 // Also set the RTP timestamp. (As above, we do this for each frame
156 // in the packet.)
157 setTimestamp(framePresentationTime);
158
159 // Set the RTP 'M' (marker) bit iff this frame ends (i.e., is the last
160 // slice of) a picture (and there are no fragments remaining).
161 // This relies on the source being a "MPEG1or2VideoStreamFramer".
162 MPEG1or2VideoStreamFramer* framerSource = (MPEG1or2VideoStreamFramer*)fSource;
163 if (framerSource != NULL && framerSource->pictureEndMarker()
164 && numRemainingBytes == 0) {
165 setMarkerBit();
166 framerSource->pictureEndMarker() = False;
167 }
168
169 fPreviousFrameWasSlice = thisFrameIsASlice;
170}
171
172unsigned MPEG1or2VideoRTPSink::specialHeaderSize() const {
173 // There's a 4 byte special video header:
174 return 4;
175}
176