2 * RTP parser for H.261 payload format (RFC 4587)
3 * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com>
5 * This file is part of Libav.
7 * Libav 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.
12 * Libav 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.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with Libav; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22 #include "libavcodec/get_bits.h"
24 #include "rtpdec_formats.h"
26 #define RTP_H261_PAYLOAD_HEADER_SIZE 4
28 struct PayloadContext {
35 static void h261_free_dyn_buffer(AVIOContext **dyn_buf)
37 uint8_t *ptr_dyn_buffer;
38 avio_close_dyn_buf(*dyn_buf, &ptr_dyn_buffer);
39 av_free(ptr_dyn_buffer);
43 static av_cold void h261_free_context(PayloadContext *pl_ctx)
45 /* return if context is invalid */
49 /* free buffer if it is valid */
51 h261_free_dyn_buffer(&pl_ctx->buf);
55 static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx,
56 AVStream *st, AVPacket *pkt, uint32_t *timestamp,
57 const uint8_t *buf, int len, uint16_t seq,
60 int sbit, ebit, gobn, mbap, quant;
63 /* drop data of previous packets in case of non-continuous (lossy) packet stream */
64 if (rtp_h261_ctx->buf && rtp_h261_ctx->timestamp != *timestamp) {
65 h261_free_dyn_buffer(&rtp_h261_ctx->buf);
66 rtp_h261_ctx->endbyte_bits = 0;
69 /* sanity check for size of input packet: 1 byte payload at least */
70 if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) {
71 av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len);
72 return AVERROR_INVALIDDATA;
76 * decode the H.261 payload header according to section 4.1 of RFC 4587:
77 * (uses 4 bytes between RTP header and H.261 stream per packet)
80 * 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
81 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
82 * |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD |
83 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
85 * Start bit position (SBIT): 3 bits
86 * End bit position (EBIT): 3 bits
87 * INTRA-frame encoded data (I): 1 bit
88 * Motion Vector flag (V): 1 bit
89 * GOB number (GOBN): 4 bits
90 * Macroblock address predictor (MBAP): 5 bits
91 * Quantizer (QUANT): 5 bits
92 * Horizontal motion vector data (HMVD): 5 bits
93 * Vertical motion vector data (VMVD): 5 bits
95 sbit = (buf[0] >> 5) & 0x07;
96 ebit = (buf[0] >> 2) & 0x07;
97 gobn = (buf[1] >> 4) & 0x0f;
98 mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01);
99 quant = (buf[2] >> 2) & 0x1f;
101 /* pass the H.261 payload header and continue with the actual payload */
102 buf += RTP_H261_PAYLOAD_HEADER_SIZE;
103 len -= RTP_H261_PAYLOAD_HEADER_SIZE;
105 /* start frame buffering with new dynamic buffer */
106 if (!rtp_h261_ctx->buf) {
107 /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, quant=0 */
108 if (!gobn && !sbit && !mbap && !quant) {
109 res = avio_open_dyn_buf(&rtp_h261_ctx->buf);
112 /* update the timestamp in the frame packet with the one from the RTP packet */
113 rtp_h261_ctx->timestamp = *timestamp;
115 /* frame not started yet, need more packets */
116 return AVERROR(EAGAIN);
120 /* do the "byte merging" at the boundaries of two consecutive frame fragments */
121 if (rtp_h261_ctx->endbyte_bits || sbit) {
122 if (rtp_h261_ctx->endbyte_bits == sbit) {
123 rtp_h261_ctx->endbyte |= buf[0] & (0xff >> sbit);
124 rtp_h261_ctx->endbyte_bits = 0;
127 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
129 /* ebit/sbit values inconsistent, assuming packet loss */
131 init_get_bits(&gb, buf, len*8 - ebit);
132 skip_bits(&gb, sbit);
133 if (rtp_h261_ctx->endbyte_bits) {
134 rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits);
135 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
137 while (get_bits_left(&gb) >= 8)
138 avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8));
139 rtp_h261_ctx->endbyte_bits = get_bits_left(&gb);
140 if (rtp_h261_ctx->endbyte_bits)
141 rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) <<
142 (8 - rtp_h261_ctx->endbyte_bits);
149 avio_write(rtp_h261_ctx->buf, buf, len - 1);
150 rtp_h261_ctx->endbyte_bits = 8 - ebit;
151 rtp_h261_ctx->endbyte = buf[len - 1] & (0xff << ebit);
153 avio_write(rtp_h261_ctx->buf, buf, len);
156 /* RTP marker bit means: last fragment of current frame was received;
157 otherwise, an additional fragment is needed for the current frame */
158 if (!(flags & RTP_FLAG_MARKER))
159 return AVERROR(EAGAIN);
161 /* write the completed last byte from the "byte merging" */
162 if (rtp_h261_ctx->endbyte_bits)
163 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
164 rtp_h261_ctx->endbyte_bits = 0;
166 /* close frame buffering and create resulting A/V packet */
167 res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index);
174 RTPDynamicProtocolHandler ff_h261_dynamic_handler = {
176 .codec_type = AVMEDIA_TYPE_VIDEO,
177 .codec_id = AV_CODEC_ID_H261,
178 .need_parsing = AVSTREAM_PARSE_FULL,
179 .priv_data_size = sizeof(PayloadContext),
180 .free = h261_free_context,
181 .parse_packet = h261_handle_packet,
182 .static_payload_id = 31,