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2ba45a60 DM |
1 | /* |
2 | * RTP parser for H.261 payload format (RFC 4587) | |
3 | * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com> | |
4 | * | |
5 | * This file is part of FFmpeg. | |
6 | * | |
7 | * FFmpeg is free software; you can redistribute it and/or | |
8 | * modify it under the terms of the GNU Lesser General Public | |
9 | * License as published by the Free Software Foundation; either | |
10 | * version 2.1 of the License, or (at your option) any later version. | |
11 | * | |
12 | * FFmpeg is distributed in the hope that it will be useful, | |
13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | * Lesser General Public License for more details. | |
16 | * | |
17 | * You should have received a copy of the GNU Lesser General Public | |
18 | * License along with FFmpeg; if not, write to the Free Software | |
19 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
20 | */ | |
21 | ||
22 | #include "avformat.h" | |
23 | #include "rtpdec_formats.h" | |
24 | #include "libavcodec/get_bits.h" | |
25 | ||
26 | #define RTP_H261_PAYLOAD_HEADER_SIZE 4 | |
27 | ||
28 | struct PayloadContext { | |
29 | AVIOContext *buf; | |
30 | uint8_t endbyte; | |
31 | int endbyte_bits; | |
32 | uint32_t timestamp; | |
33 | }; | |
34 | ||
35 | static PayloadContext *h261_new_context(void) | |
36 | { | |
37 | return av_mallocz(sizeof(PayloadContext)); | |
38 | } | |
39 | ||
40 | static void h261_free_dyn_buffer(AVIOContext **dyn_buf) | |
41 | { | |
42 | uint8_t *ptr_dyn_buffer; | |
43 | avio_close_dyn_buf(*dyn_buf, &ptr_dyn_buffer); | |
44 | av_free(ptr_dyn_buffer); | |
45 | *dyn_buf = NULL; | |
46 | } | |
47 | ||
48 | static void h261_free_context(PayloadContext *pl_ctx) | |
49 | { | |
50 | /* return if context is invalid */ | |
51 | if (!pl_ctx) | |
52 | return; | |
53 | ||
54 | /* free buffer if it is valid */ | |
55 | if (pl_ctx->buf) { | |
56 | h261_free_dyn_buffer(&pl_ctx->buf); | |
57 | } | |
58 | ||
59 | /* free context */ | |
60 | av_free(pl_ctx); | |
61 | } | |
62 | ||
63 | static av_cold int h261_init(AVFormatContext *ctx, int st_index, | |
64 | PayloadContext *data) | |
65 | { | |
66 | //av_log(ctx, AV_LOG_DEBUG, "h261_init() for stream %d\n", st_index); | |
67 | ||
68 | if (st_index < 0) | |
69 | return 0; | |
70 | ||
71 | ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL; | |
72 | ||
73 | return 0; | |
74 | } | |
75 | ||
76 | int ff_h261_handle_packet(AVFormatContext *ctx, PayloadContext *data, | |
77 | AVStream *st, AVPacket *pkt, uint32_t *timestamp, | |
78 | const uint8_t *buf, int len, uint16_t seq, int flags) | |
79 | { | |
80 | int sbit, ebit, gobn, mbap, quant; | |
81 | int res; | |
82 | ||
83 | //av_log(ctx, AV_LOG_DEBUG, "got h261 RTP packet with time: %u\n", timestamp); | |
84 | ||
85 | /* drop data of previous packets in case of non-continuous (loss) packet stream */ | |
86 | if (data->buf && data->timestamp != *timestamp) { | |
87 | h261_free_dyn_buffer(&data->buf); | |
88 | } | |
89 | ||
90 | /* sanity check for size of input packet */ | |
91 | if (len < 5 /* 4 bytes header and 1 byte payload at least */) { | |
92 | av_log(ctx, AV_LOG_ERROR, "Too short H.261 RTP packet\n"); | |
93 | return AVERROR_INVALIDDATA; | |
94 | } | |
95 | ||
96 | /* | |
97 | decode the H.261 payload header according to section 4.1 of RFC 4587: | |
98 | (uses 4 bytes between RTP header and H.261 stream per packet) | |
99 | ||
100 | 0 1 2 3 | |
101 | 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 | |
102 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
103 | |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD | | |
104 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
105 | ||
106 | Start bit position (SBIT): 3 bits | |
107 | End bit position (EBIT): 3 bits | |
108 | INTRA-frame encoded data (I): 1 bit | |
109 | Motion Vector flag (V): 1 bit | |
110 | GOB number (GOBN): 4 bits | |
111 | Macroblock address predictor (MBAP): 5 bits | |
112 | Quantizer (QUANT): 5 bits | |
113 | Horizontal motion vector data (HMVD): 5 bits | |
114 | Vertical motion vector data (VMVD): 5 bits | |
115 | ||
116 | */ | |
117 | sbit = (buf[0] >> 5) & 0x07; | |
118 | ebit = (buf[0] >> 2) & 0x07; | |
119 | gobn = (buf[1] >> 4) & 0x0f; | |
120 | mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01); | |
121 | quant = (buf[2] >> 2) & 0x1f; | |
122 | ||
123 | /* pass the H.261 payload header and continue with the actual payload */ | |
124 | buf += RTP_H261_PAYLOAD_HEADER_SIZE; | |
125 | len -= RTP_H261_PAYLOAD_HEADER_SIZE; | |
126 | ||
127 | /* start frame buffering with new dynamic buffer */ | |
128 | if (!data->buf) { | |
129 | /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, uqnat=0 */ | |
130 | if (!gobn && !sbit && !mbap && !quant){ | |
131 | res = avio_open_dyn_buf(&data->buf); | |
132 | if (res < 0) | |
133 | return res; | |
134 | /* update the timestamp in the frame packet with the one from the RTP packet */ | |
135 | data->timestamp = *timestamp; | |
136 | } else { | |
137 | /* frame not started yet, need more packets */ | |
138 | return AVERROR(EAGAIN); | |
139 | } | |
140 | } | |
141 | ||
142 | /* do the "byte merging" at the boundaries of two consecutive frame fragments */ | |
143 | if (data->endbyte_bits || sbit) { | |
144 | if (data->endbyte_bits == sbit) { | |
145 | data->endbyte |= buf[0] & (0xff >> sbit); | |
146 | data->endbyte_bits = 0; | |
147 | buf++; | |
148 | len--; | |
149 | avio_w8(data->buf, data->endbyte); | |
150 | } else { | |
151 | /* ebit/sbit values inconsistent, assuming packet loss */ | |
152 | GetBitContext gb; | |
153 | init_get_bits(&gb, buf, len*8 - ebit); | |
154 | skip_bits(&gb, sbit); | |
155 | if (data->endbyte_bits) { | |
156 | data->endbyte |= get_bits(&gb, 8 - data->endbyte_bits); | |
157 | avio_w8(data->buf, data->endbyte); | |
158 | } | |
159 | while (get_bits_left(&gb) >= 8) | |
160 | avio_w8(data->buf, get_bits(&gb, 8)); | |
161 | data->endbyte_bits = get_bits_left(&gb); | |
162 | if (data->endbyte_bits) | |
163 | data->endbyte = get_bits(&gb, data->endbyte_bits) << | |
164 | (8 - data->endbyte_bits); | |
165 | ebit = 0; | |
166 | len = 0; | |
167 | } | |
168 | } | |
169 | if (ebit) { | |
170 | if (len > 0) | |
171 | avio_write(data->buf, buf, len - 1); | |
172 | data->endbyte_bits = 8 - ebit; | |
173 | data->endbyte = buf[len - 1] & (0xff << ebit); | |
174 | } else { | |
175 | avio_write(data->buf, buf, len); | |
176 | } | |
177 | ||
178 | /* RTP marker bit means: last fragment of current frame was received; | |
179 | otherwise, an additional fragment is needed for the current frame */ | |
180 | if (!(flags & RTP_FLAG_MARKER)) | |
181 | return AVERROR(EAGAIN); | |
182 | ||
183 | /* write the completed last byte from the "byte merging" */ | |
184 | if (data->endbyte_bits) | |
185 | avio_w8(data->buf, data->endbyte); | |
186 | data->endbyte_bits = 0; | |
187 | ||
188 | /* close frame buffering and create resulting A/V packet */ | |
189 | res = ff_rtp_finalize_packet(pkt, &data->buf, st->index); | |
190 | if (res < 0) | |
191 | return res; | |
192 | ||
193 | return 0; | |
194 | } | |
195 | ||
196 | RTPDynamicProtocolHandler ff_h261_dynamic_handler = { | |
197 | .enc_name = "H261", | |
198 | .codec_type = AVMEDIA_TYPE_VIDEO, | |
199 | .codec_id = AV_CODEC_ID_H261, | |
200 | .init = h261_init, | |
201 | .parse_packet = ff_h261_handle_packet, | |
202 | .alloc = h261_new_context, | |
203 | .free = h261_free_context, | |
204 | .static_payload_id = 31, | |
205 | }; |