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
h261_new_context(void)35 static PayloadContext *h261_new_context(void)
36 {
37 return av_mallocz(sizeof(PayloadContext));
38 }
39
h261_free_dyn_buffer(AVIOContext ** dyn_buf)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
h261_free_context(PayloadContext * pl_ctx)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
h261_init(AVFormatContext * ctx,int st_index,PayloadContext * data)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
ff_h261_handle_packet(AVFormatContext * ctx,PayloadContext * data,AVStream * st,AVPacket * pkt,uint32_t * timestamp,const uint8_t * buf,int len,uint16_t seq,int flags)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 };
206