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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 
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 */
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 };
RTPDynamicProtocolHandler ff_h261_dynamic_handler
Definition: rtpdec_h261.c:165
Bytestream IO Context.
Definition: avio.h:111
#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:260
RTP/JPEG specific private data.
Definition: rdt.c:83
int index
stream index in AVFormatContext
Definition: avformat.h:843
static AVPacket pkt
int avio_open_dyn_buf(AVIOContext **s)
Open a write only memory stream.
Definition: aviobuf.c:1113
Format I/O context.
Definition: avformat.h:1272
uint8_t
#define av_cold
Definition: attributes.h:74
bitstream reader API header.
void avio_write(AVIOContext *s, const unsigned char *buf, int size)
Definition: aviobuf.c:177
#define av_log(a,...)
static int get_bits_left(GetBitContext *gb)
Definition: get_bits.h:588
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
#define AVERROR(e)
Definition: error.h:43
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:1153
Stream structure.
Definition: avformat.h:842
void avio_w8(AVIOContext *s, int b)
Definition: aviobuf.c:155
void * buf
Definition: avisynth_c.h:553
static void skip_bits(GetBitContext *s, int n)
Definition: get_bits.h:297
static int init_get_bits(GetBitContext *s, const uint8_t *buffer, int bit_size)
Initialize GetBitContext.
Definition: get_bits.h:410
uint8_t * buf
the temporary storage buffer
Definition: rtpdec_asf.c:185
const char * enc_name
Definition: rtpdec.h:116
const uint8_t * quant
static int flags
Definition: cpu.c:47
full parsing and repack
Definition: avformat.h:774
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:888
static int parse_packet(AVFormatContext *s, AVPacket *pkt, int stream_index)
Parse a packet, add all split parts to parse_queue.
Definition: utils.c:1187
int len
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
This structure stores compressed data.
Definition: avcodec.h:1139