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 FFmpeg.
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.
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.
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
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);
58 static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx,
59 AVStream *st, AVPacket *pkt, uint32_t *timestamp,
60 const uint8_t *buf, int len, uint16_t seq,
63 int sbit, ebit, gobn, mbap, quant;
66 /* drop data of previous packets in case of non-continuous (lossy) packet stream */
67 if (rtp_h261_ctx->buf && rtp_h261_ctx->timestamp != *timestamp) {
68 h261_free_dyn_buffer(&rtp_h261_ctx->buf);
69 rtp_h261_ctx->endbyte_bits = 0;
72 /* sanity check for size of input packet: 1 byte payload at least */
73 if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) {
74 av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len);
75 return AVERROR_INVALIDDATA;
79 * decode the H.261 payload header according to section 4.1 of RFC 4587:
80 * (uses 4 bytes between RTP header and H.261 stream per packet)
83 * 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
84 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
85 * |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD |
86 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
88 * Start bit position (SBIT): 3 bits
89 * End bit position (EBIT): 3 bits
90 * INTRA-frame encoded data (I): 1 bit
91 * Motion Vector flag (V): 1 bit
92 * GOB number (GOBN): 4 bits
93 * Macroblock address predictor (MBAP): 5 bits
94 * Quantizer (QUANT): 5 bits
95 * Horizontal motion vector data (HMVD): 5 bits
96 * Vertical motion vector data (VMVD): 5 bits
98 sbit = (buf[0] >> 5) & 0x07;
99 ebit = (buf[0] >> 2) & 0x07;
100 gobn = (buf[1] >> 4) & 0x0f;
101 mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01);
102 quant = (buf[2] >> 2) & 0x1f;
104 /* pass the H.261 payload header and continue with the actual payload */
105 buf += RTP_H261_PAYLOAD_HEADER_SIZE;
106 len -= RTP_H261_PAYLOAD_HEADER_SIZE;
108 /* start frame buffering with new dynamic buffer */
109 if (!rtp_h261_ctx->buf) {
110 /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, quant=0 */
111 if (!gobn && !sbit && !mbap && !quant) {
112 res = avio_open_dyn_buf(&rtp_h261_ctx->buf);
115 /* update the timestamp in the frame packet with the one from the RTP packet */
116 rtp_h261_ctx->timestamp = *timestamp;
118 /* frame not started yet, need more packets */
119 return AVERROR(EAGAIN);
123 /* do the "byte merging" at the boundaries of two consecutive frame fragments */
124 if (rtp_h261_ctx->endbyte_bits || sbit) {
125 if (rtp_h261_ctx->endbyte_bits == sbit) {
126 rtp_h261_ctx->endbyte |= buf[0] & (0xff >> sbit);
127 rtp_h261_ctx->endbyte_bits = 0;
130 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
132 /* ebit/sbit values inconsistent, assuming packet loss */
134 init_get_bits(&gb, buf, len*8 - ebit);
135 skip_bits(&gb, sbit);
136 if (rtp_h261_ctx->endbyte_bits) {
137 rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits);
138 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
140 while (get_bits_left(&gb) >= 8)
141 avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8));
142 rtp_h261_ctx->endbyte_bits = get_bits_left(&gb);
143 if (rtp_h261_ctx->endbyte_bits)
144 rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) <<
145 (8 - rtp_h261_ctx->endbyte_bits);
152 avio_write(rtp_h261_ctx->buf, buf, len - 1);
153 rtp_h261_ctx->endbyte_bits = 8 - ebit;
154 rtp_h261_ctx->endbyte = buf[len - 1] & (0xff << ebit);
156 avio_write(rtp_h261_ctx->buf, buf, len);
159 /* RTP marker bit means: last fragment of current frame was received;
160 otherwise, an additional fragment is needed for the current frame */
161 if (!(flags & RTP_FLAG_MARKER))
162 return AVERROR(EAGAIN);
164 /* write the completed last byte from the "byte merging" */
165 if (rtp_h261_ctx->endbyte_bits)
166 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
167 rtp_h261_ctx->endbyte_bits = 0;
169 /* close frame buffering and create resulting A/V packet */
170 res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index);
177 RTPDynamicProtocolHandler ff_h261_dynamic_handler = {
179 .codec_type = AVMEDIA_TYPE_VIDEO,
180 .codec_id = AV_CODEC_ID_H261,
181 .need_parsing = AVSTREAM_PARSE_FULL,
182 .priv_data_size = sizeof(PayloadContext),
183 .free = h261_free_context,
184 .parse_packet = h261_handle_packet,
185 .static_payload_id = 31,