FFmpeg
rtpdec_h261.c
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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 {
33  uint32_t timestamp;
34 };
35 
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 
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 */
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 
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,
173  .static_payload_id = 31,
174 };
AVPacket pkt
Definition: rtpdec_qt.c:37
Bytestream IO Context.
Definition: avio.h:161
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:59
uint8_t endbyte
Definition: rtpdec_h261.c:31
static unsigned int get_bits(GetBitContext *s, int n)
Read 1-25 bits.
Definition: get_bits.h:379
RTP/JPEG specific private data.
Definition: rdt.c:83
int index
stream index in AVFormatContext
Definition: avformat.h:882
const RTPDynamicProtocolHandler ff_h261_dynamic_handler
Definition: rtpdec_h261.c:165
int avio_open_dyn_buf(AVIOContext **s)
Open a write only memory stream.
Definition: aviobuf.c:1430
Format I/O context.
Definition: avformat.h:1358
uint8_t
#define av_cold
Definition: attributes.h:82
bitstream reader API header.
void avio_write(AVIOContext *s, const unsigned char *buf, int size)
Definition: aviobuf.c:218
#define av_log(a,...)
static int get_bits_left(GetBitContext *gb)
Definition: get_bits.h:849
uint32_t timestamp
current frame timestamp
Definition: rtpdec_ac3.c:31
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:176
#define RTP_FLAG_MARKER
RTP marker bit was set for this packet.
Definition: rtpdec.h:93
AVFormatContext * ctx
Definition: movenc.c:48
static av_cold void h261_close_context(PayloadContext *pl_ctx)
Definition: rtpdec_h261.c:36
#define RTP_H261_PAYLOAD_HEADER_SIZE
Definition: rtpdec_h261.c:27
void ffio_free_dyn_buf(AVIOContext **s)
Free a dynamic buffer.
Definition: aviobuf.c:1489
Stream structure.
Definition: avformat.h:881
void avio_w8(AVIOContext *s, int b)
Definition: aviobuf.c:196
static void skip_bits(GetBitContext *s, int n)
Definition: get_bits.h:467
static int init_get_bits(GetBitContext *s, const uint8_t *buffer, int bit_size)
Initialize GetBitContext.
Definition: get_bits.h:659
uint8_t * buf
the temporary storage buffer
Definition: rtpdec_asf.c:183
const char * enc_name
Definition: rtpdec.h:116
const uint8_t * quant
#define flags(name, subs,...)
Definition: cbs_av1.c:561
full parsing and repack
Definition: avformat.h:800
Main libavformat public API header.
int ff_rtp_finalize_packet(AVPacket *pkt, AVIOContext **dyn_buf, int stream_idx)
Close the dynamic buffer and make a packet from it.
Definition: rtpdec.c:927
static int parse_packet(AVFormatContext *s, AVPacket *pkt, int stream_index)
Parse a packet, add all split parts to parse_queue.
Definition: utils.c:1438
static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx, AVStream *st, AVPacket *pkt, uint32_t *timestamp, const uint8_t *buf, int len, uint16_t seq, int flags)
Definition: rtpdec_h261.c:46
Filter the word “frame” indicates either a video frame or a group of audio as stored in an AVFrame structure Format for each input and each output the list of supported formats For video that means pixel format For audio that means channel sample they are references to shared objects When the negotiation mechanism computes the intersection of the formats supported at each end of a all references to both lists are replaced with a reference to the intersection And when a single format is eventually chosen for a link amongst the remaining all references to the list are updated That means that if a filter requires that its input and output have the same format amongst a supported all it has to do is use a reference to the same list of formats query_formats can leave some formats unset and return AVERROR(EAGAIN) to cause the negotiation mechanism toagain later.That can be used by filters with complex requirements to use the format negotiated on one link to set the formats supported on another.Frame references ownership and permissions
This structure stores compressed data.
Definition: avcodec.h:1456