FFmpeg coverage

Directory: ../../../ffmpeg/
File: src/libavformat/rtpdec_h261.c
Date: 2026-10-15 16:30:37
Exec Total Coverage
Lines: 0 68 0.0%
Functions: 0 2 0.0%
Branches: 0 52 0.0%
Line Branch Exec Source
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
29 struct PayloadContext {
30 AVIOContext *buf;
31 uint8_t endbyte;
32 int endbyte_bits;
33 uint32_t timestamp;
34 };
35
36 ✗ static 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
46 ✗ static 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 ✗ buf++;
116 ✗ len--;
117 ✗ if (!len && ebit) {
118 ✗ rtp_h261_ctx->endbyte &= 0xff << ebit;
119 ✗ rtp_h261_ctx->endbyte_bits = 8 - ebit;
120 ✗ ebit = 0;
121 } else {
122 ✗ rtp_h261_ctx->endbyte_bits = 0;
123 ✗ avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
124 }
125 } else {
126 /* ebit/sbit values inconsistent, assuming packet loss */
127 GetBitContext gb;
128 ✗ res = init_get_bits(&gb, buf, len*8 - ebit);
129 ✗ if (res < 0)
130 ✗ return res;
131 ✗ if (get_bits_left(&gb) < sbit + (rtp_h261_ctx->endbyte_bits ? 8 - rtp_h261_ctx->endbyte_bits : 0))
132 ✗ return AVERROR_INVALIDDATA;
133 ✗ skip_bits(&gb, sbit);
134 ✗ if (rtp_h261_ctx->endbyte_bits) {
135 ✗ rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits);
136 ✗ avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
137 }
138 ✗ while (get_bits_left(&gb) >= 8)
139 ✗ avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8));
140 ✗ rtp_h261_ctx->endbyte_bits = get_bits_left(&gb);
141 ✗ if (rtp_h261_ctx->endbyte_bits)
142 ✗ rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) <<
143 ✗ (8 - rtp_h261_ctx->endbyte_bits);
144 ✗ ebit = 0;
145 ✗ len = 0;
146 }
147 }
148 ✗ if (ebit) {
149 ✗ if (len > 0)
150 ✗ avio_write(rtp_h261_ctx->buf, buf, len - 1);
151 ✗ rtp_h261_ctx->endbyte_bits = 8 - ebit;
152 ✗ rtp_h261_ctx->endbyte = buf[len - 1] & (0xff << ebit);
153 } else {
154 ✗ avio_write(rtp_h261_ctx->buf, buf, len);
155 }
156
157 /* RTP marker bit means: last fragment of current frame was received;
158 otherwise, an additional fragment is needed for the current frame */
159 ✗ if (!(flags & RTP_FLAG_MARKER))
160 ✗ return AVERROR(EAGAIN);
161
162 /* write the completed last byte from the "byte merging" */
163 ✗ if (rtp_h261_ctx->endbyte_bits)
164 ✗ avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
165 ✗ rtp_h261_ctx->endbyte_bits = 0;
166
167 /* close frame buffering and create resulting A/V packet */
168 ✗ res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index);
169 ✗ if (res < 0)
170 ✗ return res;
171
172 ✗ return 0;
173 }
174
175 const RTPDynamicProtocolHandler ff_h261_dynamic_handler = {
176 .enc_name = "H261",
177 .codec_type = AVMEDIA_TYPE_VIDEO,
178 .codec_id = AV_CODEC_ID_H261,
179 .need_parsing = AVSTREAM_PARSE_FULL,
180 .priv_data_size = sizeof(PayloadContext),
181 .close = h261_close_context,
182 .parse_packet = h261_handle_packet,
183 .static_payload_id = 31,
184 };
185