FFmpeg
 All Data Structures Namespaces Files Functions Variables Typedefs Enumerations Enumerator Macros Groups Pages
mxg.c
Go to the documentation of this file.
1 /*
2  * MxPEG clip file demuxer
3  * Copyright (c) 2010 Anatoly Nenashev
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 
23 #include "libavutil/intreadwrite.h"
24 #include "libavcodec/mjpeg.h"
25 #include "avformat.h"
26 #include "internal.h"
27 #include "avio.h"
28 
29 #define DEFAULT_PACKET_SIZE 1024
30 #define OVERREAD_SIZE 3
31 
32 typedef struct MXGContext {
36  unsigned int buffer_size;
37  int64_t dts;
38  unsigned int cache_size;
39 } MXGContext;
40 
42 {
43  AVStream *video_st, *audio_st;
44  MXGContext *mxg = s->priv_data;
45 
46  /* video parameters will be extracted from the compressed bitstream */
47  video_st = avformat_new_stream(s, NULL);
48  if (!video_st)
49  return AVERROR(ENOMEM);
50  video_st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
51  video_st->codec->codec_id = AV_CODEC_ID_MXPEG;
52  avpriv_set_pts_info(video_st, 64, 1, 1000000);
53 
54  audio_st = avformat_new_stream(s, NULL);
55  if (!audio_st)
56  return AVERROR(ENOMEM);
57  audio_st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
58  audio_st->codec->codec_id = AV_CODEC_ID_PCM_ALAW;
59  audio_st->codec->channels = 1;
61  audio_st->codec->sample_rate = 8000;
62  audio_st->codec->bits_per_coded_sample = 8;
63  audio_st->codec->block_align = 1;
64  avpriv_set_pts_info(audio_st, 64, 1, 1000000);
65 
66  mxg->soi_ptr = mxg->buffer_ptr = mxg->buffer = 0;
67  mxg->buffer_size = 0;
68  mxg->dts = AV_NOPTS_VALUE;
69  mxg->cache_size = 0;
70 
71  return 0;
72 }
73 
75 {
76  for (; p < end - 3; p += 4) {
77  uint32_t x = AV_RN32(p);
78 
79  if (x & (~(x+0x01010101)) & 0x80808080) {
80  if (p[0] == 0xff) {
81  return p;
82  } else if (p[1] == 0xff) {
83  return p+1;
84  } else if (p[2] == 0xff) {
85  return p+2;
86  } else if (p[3] == 0xff) {
87  return p+3;
88  }
89  }
90  }
91 
92  for (; p < end; ++p) {
93  if (*p == 0xff) return p;
94  }
95 
96  return end;
97 }
98 
99 static int mxg_update_cache(AVFormatContext *s, unsigned int cache_size)
100 {
101  MXGContext *mxg = s->priv_data;
102  unsigned int current_pos = mxg->buffer_ptr - mxg->buffer;
103  unsigned int soi_pos;
104  uint8_t *buffer;
105  int ret;
106 
107  /* reallocate internal buffer */
108  if (current_pos > current_pos + cache_size)
109  return AVERROR(ENOMEM);
110  soi_pos = mxg->soi_ptr - mxg->buffer;
111  buffer = av_fast_realloc(mxg->buffer, &mxg->buffer_size,
112  current_pos + cache_size +
114  if (!buffer)
115  return AVERROR(ENOMEM);
116  mxg->buffer = buffer;
117  mxg->buffer_ptr = mxg->buffer + current_pos;
118  if (mxg->soi_ptr) mxg->soi_ptr = mxg->buffer + soi_pos;
119 
120  /* get data */
121  ret = avio_read(s->pb, mxg->buffer_ptr + mxg->cache_size,
122  cache_size - mxg->cache_size);
123  if (ret < 0)
124  return ret;
125 
126  mxg->cache_size += ret;
127 
128  return ret;
129 }
130 
132 {
133  int ret;
134  unsigned int size;
135  uint8_t *startmarker_ptr, *end, *search_end, marker;
136  MXGContext *mxg = s->priv_data;
137 
138  while (!url_feof(s->pb) && !s->pb->error){
139  if (mxg->cache_size <= OVERREAD_SIZE) {
140  /* update internal buffer */
142  if (ret < 0)
143  return ret;
144  }
145  end = mxg->buffer_ptr + mxg->cache_size;
146 
147  /* find start marker - 0xff */
148  if (mxg->cache_size > OVERREAD_SIZE) {
149  search_end = end - OVERREAD_SIZE;
150  startmarker_ptr = mxg_find_startmarker(mxg->buffer_ptr, search_end);
151  } else {
152  search_end = end;
153  startmarker_ptr = mxg_find_startmarker(mxg->buffer_ptr, search_end);
154  if (startmarker_ptr >= search_end - 1 ||
155  *(startmarker_ptr + 1) != EOI) break;
156  }
157 
158  if (startmarker_ptr != search_end) { /* start marker found */
159  marker = *(startmarker_ptr + 1);
160  mxg->buffer_ptr = startmarker_ptr + 2;
161  mxg->cache_size = end - mxg->buffer_ptr;
162 
163  if (marker == SOI) {
164  mxg->soi_ptr = startmarker_ptr;
165  } else if (marker == EOI) {
166  if (!mxg->soi_ptr) {
167  av_log(s, AV_LOG_WARNING, "Found EOI before SOI, skipping\n");
168  continue;
169  }
170 
171  pkt->pts = pkt->dts = mxg->dts;
172  pkt->stream_index = 0;
173 #if FF_API_DESTRUCT_PACKET
174  pkt->destruct = NULL;
175 #endif
176  pkt->buf = NULL;
177  pkt->size = mxg->buffer_ptr - mxg->soi_ptr;
178  pkt->data = mxg->soi_ptr;
179 
180  if (mxg->soi_ptr - mxg->buffer > mxg->cache_size) {
181  if (mxg->cache_size > 0) {
182  memcpy(mxg->buffer, mxg->buffer_ptr, mxg->cache_size);
183  }
184 
185  mxg->buffer_ptr = mxg->buffer;
186  }
187  mxg->soi_ptr = 0;
188 
189  return pkt->size;
190  } else if ( (SOF0 <= marker && marker <= SOF15) ||
191  (SOS <= marker && marker <= COM) ) {
192  /* all other markers that start marker segment also contain
193  length value (see specification for JPEG Annex B.1) */
194  size = AV_RB16(mxg->buffer_ptr);
195  if (size < 2)
196  return AVERROR(EINVAL);
197 
198  if (mxg->cache_size < size) {
199  ret = mxg_update_cache(s, size);
200  if (ret < 0)
201  return ret;
202  startmarker_ptr = mxg->buffer_ptr - 2;
203  mxg->cache_size = 0;
204  } else {
205  mxg->cache_size -= size;
206  }
207 
208  mxg->buffer_ptr += size;
209 
210  if (marker == APP13 && size >= 16) { /* audio data */
211  /* time (GMT) of first sample in usec since 1970, little-endian */
212  pkt->pts = pkt->dts = AV_RL64(startmarker_ptr + 8);
213  pkt->stream_index = 1;
214 #if FF_API_DESTRUCT_PACKET
215  pkt->destruct = NULL;
216 #endif
217  pkt->buf = NULL;
218  pkt->size = size - 14;
219  pkt->data = startmarker_ptr + 16;
220 
221  if (startmarker_ptr - mxg->buffer > mxg->cache_size) {
222  if (mxg->cache_size > 0) {
223  memcpy(mxg->buffer, mxg->buffer_ptr, mxg->cache_size);
224  }
225  mxg->buffer_ptr = mxg->buffer;
226  }
227 
228  return pkt->size;
229  } else if (marker == COM && size >= 18 &&
230  !strncmp(startmarker_ptr + 4, "MXF", 3)) {
231  /* time (GMT) of video frame in usec since 1970, little-endian */
232  mxg->dts = AV_RL64(startmarker_ptr + 12);
233  }
234  }
235  } else {
236  /* start marker not found */
237  mxg->buffer_ptr = search_end;
238  mxg->cache_size = OVERREAD_SIZE;
239  }
240  }
241 
242  return AVERROR_EOF;
243 }
244 
245 static int mxg_close(struct AVFormatContext *s)
246 {
247  MXGContext *mxg = s->priv_data;
248  av_freep(&mxg->buffer);
249  return 0;
250 }
251 
253  .name = "mxg",
254  .long_name = NULL_IF_CONFIG_SMALL("MxPEG clip"),
255  .priv_data_size = sizeof(MXGContext),
259  .extensions = "mxg",
260 };