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 av_cold PayloadContext *h261_new_context(void)
37 return av_mallocz(sizeof(PayloadContext));
40 static void h261_free_dyn_buffer(AVIOContext **dyn_buf)
42 uint8_t *ptr_dyn_buffer;
43 avio_close_dyn_buf(*dyn_buf, &ptr_dyn_buffer);
44 av_free(ptr_dyn_buffer);
48 static av_cold void h261_free_context(PayloadContext *pl_ctx)
50 /* return if context is invalid */
54 /* free buffer if it is valid */
56 h261_free_dyn_buffer(&pl_ctx->buf);
63 static av_cold int h261_init(AVFormatContext *ctx, int st_index,
69 ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL;
74 static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx,
75 AVStream *st, AVPacket *pkt, uint32_t *timestamp,
76 const uint8_t *buf, int len, uint16_t seq,
79 int sbit, ebit, gobn, mbap, quant;
82 /* drop data of previous packets in case of non-continuous (lossy) packet stream */
83 if (rtp_h261_ctx->buf && rtp_h261_ctx->timestamp != *timestamp) {
84 h261_free_dyn_buffer(&rtp_h261_ctx->buf);
85 rtp_h261_ctx->endbyte_bits = 0;
88 /* sanity check for size of input packet: 1 byte payload at least */
89 if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) {
90 av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len);
91 return AVERROR_INVALIDDATA;
95 * decode the H.261 payload header according to section 4.1 of RFC 4587:
96 * (uses 4 bytes between RTP header and H.261 stream per packet)
99 * 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
100 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
101 * |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD |
102 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
104 * Start bit position (SBIT): 3 bits
105 * End bit position (EBIT): 3 bits
106 * INTRA-frame encoded data (I): 1 bit
107 * Motion Vector flag (V): 1 bit
108 * GOB number (GOBN): 4 bits
109 * Macroblock address predictor (MBAP): 5 bits
110 * Quantizer (QUANT): 5 bits
111 * Horizontal motion vector data (HMVD): 5 bits
112 * Vertical motion vector data (VMVD): 5 bits
114 sbit = (buf[0] >> 5) & 0x07;
115 ebit = (buf[0] >> 2) & 0x07;
116 gobn = (buf[1] >> 4) & 0x0f;
117 mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01);
118 quant = (buf[2] >> 2) & 0x1f;
120 /* pass the H.261 payload header and continue with the actual payload */
121 buf += RTP_H261_PAYLOAD_HEADER_SIZE;
122 len -= RTP_H261_PAYLOAD_HEADER_SIZE;
124 /* start frame buffering with new dynamic buffer */
125 if (!rtp_h261_ctx->buf) {
126 /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, quant=0 */
127 if (!gobn && !sbit && !mbap && !quant) {
128 res = avio_open_dyn_buf(&rtp_h261_ctx->buf);
131 /* update the timestamp in the frame packet with the one from the RTP packet */
132 rtp_h261_ctx->timestamp = *timestamp;
134 /* frame not started yet, need more packets */
135 return AVERROR(EAGAIN);
139 /* do the "byte merging" at the boundaries of two consecutive frame fragments */
140 if (rtp_h261_ctx->endbyte_bits || sbit) {
141 if (rtp_h261_ctx->endbyte_bits == sbit) {
142 rtp_h261_ctx->endbyte |= buf[0] & (0xff >> sbit);
143 rtp_h261_ctx->endbyte_bits = 0;
146 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
148 /* ebit/sbit values inconsistent, assuming packet loss */
150 init_get_bits(&gb, buf, len*8 - ebit);
151 skip_bits(&gb, sbit);
152 if (rtp_h261_ctx->endbyte_bits) {
153 rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits);
154 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
156 while (get_bits_left(&gb) >= 8)
157 avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8));
158 rtp_h261_ctx->endbyte_bits = get_bits_left(&gb);
159 if (rtp_h261_ctx->endbyte_bits)
160 rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) <<
161 (8 - rtp_h261_ctx->endbyte_bits);
168 avio_write(rtp_h261_ctx->buf, buf, len - 1);
169 rtp_h261_ctx->endbyte_bits = 8 - ebit;
170 rtp_h261_ctx->endbyte = buf[len - 1] & (0xff << ebit);
172 avio_write(rtp_h261_ctx->buf, buf, len);
175 /* RTP marker bit means: last fragment of current frame was received;
176 otherwise, an additional fragment is needed for the current frame */
177 if (!(flags & RTP_FLAG_MARKER))
178 return AVERROR(EAGAIN);
180 /* write the completed last byte from the "byte merging" */
181 if (rtp_h261_ctx->endbyte_bits)
182 avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
183 rtp_h261_ctx->endbyte_bits = 0;
185 /* close frame buffering and create resulting A/V packet */
186 res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index);
193 RTPDynamicProtocolHandler ff_h261_dynamic_handler = {
195 .codec_type = AVMEDIA_TYPE_VIDEO,
196 .codec_id = AV_CODEC_ID_H261,
198 .alloc = h261_new_context,
199 .free = h261_free_context,
200 .parse_packet = h261_handle_packet,
201 .static_payload_id = 31,