summaryrefslogtreecommitdiff
path: root/libavformat/rtpdec_h261.c (plain)
blob: 9729f21d157573dc7bfb5b9d4bdfc25ccfa5eb9f
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 "libavcodec/get_bits.h"
23#include "avformat.h"
24#include "avio_internal.h"
25#include "rtpdec_formats.h"
26
27#define RTP_H261_PAYLOAD_HEADER_SIZE 4
28
29struct PayloadContext {
30 AVIOContext *buf;
31 uint8_t endbyte;
32 int endbyte_bits;
33 uint32_t timestamp;
34};
35
36static av_cold void h261_close_context(PayloadContext *pl_ctx)
37{
38 /* return if context is invalid */
39 if (!pl_ctx)
40 return;
41
42 /* free buffer if it is valid */
43 ffio_free_dyn_buf(&pl_ctx->buf);
44}
45
46static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx,
47 AVStream *st, AVPacket *pkt, uint32_t *timestamp,
48 const uint8_t *buf, int len, uint16_t seq,
49 int flags)
50{
51 int sbit, ebit, gobn, mbap, quant;
52 int res;
53
54 /* drop data of previous packets in case of non-continuous (lossy) packet stream */
55 if (rtp_h261_ctx->buf && rtp_h261_ctx->timestamp != *timestamp) {
56 ffio_free_dyn_buf(&rtp_h261_ctx->buf);
57 rtp_h261_ctx->endbyte_bits = 0;
58 }
59
60 /* sanity check for size of input packet: 1 byte payload at least */
61 if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) {
62 av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len);
63 return AVERROR_INVALIDDATA;
64 }
65
66 /*
67 * decode the H.261 payload header according to section 4.1 of RFC 4587:
68 * (uses 4 bytes between RTP header and H.261 stream per packet)
69 *
70 * 0 1 2 3
71 * 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
72 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
73 * |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD |
74 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
75 *
76 * Start bit position (SBIT): 3 bits
77 * End bit position (EBIT): 3 bits
78 * INTRA-frame encoded data (I): 1 bit
79 * Motion Vector flag (V): 1 bit
80 * GOB number (GOBN): 4 bits
81 * Macroblock address predictor (MBAP): 5 bits
82 * Quantizer (QUANT): 5 bits
83 * Horizontal motion vector data (HMVD): 5 bits
84 * Vertical motion vector data (VMVD): 5 bits
85 */
86 sbit = (buf[0] >> 5) & 0x07;
87 ebit = (buf[0] >> 2) & 0x07;
88 gobn = (buf[1] >> 4) & 0x0f;
89 mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01);
90 quant = (buf[2] >> 2) & 0x1f;
91
92 /* pass the H.261 payload header and continue with the actual payload */
93 buf += RTP_H261_PAYLOAD_HEADER_SIZE;
94 len -= RTP_H261_PAYLOAD_HEADER_SIZE;
95
96 /* start frame buffering with new dynamic buffer */
97 if (!rtp_h261_ctx->buf) {
98 /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, quant=0 */
99 if (!gobn && !sbit && !mbap && !quant) {
100 res = avio_open_dyn_buf(&rtp_h261_ctx->buf);
101 if (res < 0)
102 return res;
103 /* update the timestamp in the frame packet with the one from the RTP packet */
104 rtp_h261_ctx->timestamp = *timestamp;
105 } else {
106 /* frame not started yet, need more packets */
107 return AVERROR(EAGAIN);
108 }
109 }
110
111 /* do the "byte merging" at the boundaries of two consecutive frame fragments */
112 if (rtp_h261_ctx->endbyte_bits || sbit) {
113 if (rtp_h261_ctx->endbyte_bits == sbit) {
114 rtp_h261_ctx->endbyte |= buf[0] & (0xff >> sbit);
115 rtp_h261_ctx->endbyte_bits = 0;
116 buf++;
117 len--;
118 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
119 } else {
120 /* ebit/sbit values inconsistent, assuming packet loss */
121 GetBitContext gb;
122 init_get_bits(&gb, buf, len*8 - ebit);
123 skip_bits(&gb, sbit);
124 if (rtp_h261_ctx->endbyte_bits) {
125 rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits);
126 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
127 }
128 while (get_bits_left(&gb) >= 8)
129 avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8));
130 rtp_h261_ctx->endbyte_bits = get_bits_left(&gb);
131 if (rtp_h261_ctx->endbyte_bits)
132 rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) <<
133 (8 - rtp_h261_ctx->endbyte_bits);
134 ebit = 0;
135 len = 0;
136 }
137 }
138 if (ebit) {
139 if (len > 0)
140 avio_write(rtp_h261_ctx->buf, buf, len - 1);
141 rtp_h261_ctx->endbyte_bits = 8 - ebit;
142 rtp_h261_ctx->endbyte = buf[len - 1] & (0xff << ebit);
143 } else {
144 avio_write(rtp_h261_ctx->buf, buf, len);
145 }
146
147 /* RTP marker bit means: last fragment of current frame was received;
148 otherwise, an additional fragment is needed for the current frame */
149 if (!(flags & RTP_FLAG_MARKER))
150 return AVERROR(EAGAIN);
151
152 /* write the completed last byte from the "byte merging" */
153 if (rtp_h261_ctx->endbyte_bits)
154 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
155 rtp_h261_ctx->endbyte_bits = 0;
156
157 /* close frame buffering and create resulting A/V packet */
158 res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index);
159 if (res < 0)
160 return res;
161
162 return 0;
163}
164
165RTPDynamicProtocolHandler ff_h261_dynamic_handler = {
166 .enc_name = "H261",
167 .codec_type = AVMEDIA_TYPE_VIDEO,
168 .codec_id = AV_CODEC_ID_H261,
169 .need_parsing = AVSTREAM_PARSE_FULL,
170 .priv_data_size = sizeof(PayloadContext),
171 .close = h261_close_context,
172 .parse_packet = h261_handle_packet,
173 .static_payload_id = 31,
174};
175
generated by cgit at 2024-05-17 01:48:37 (GMT)