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/internal.h"
24 #include "libavutil/intreadwrite.h"
25 #include "libavcodec/mjpeg.h"
26 #include "avformat.h"
27 #include "internal.h"
28 #include "avio.h"
29 
30 #define DEFAULT_PACKET_SIZE 1024
31 #define OVERREAD_SIZE 3
32 
33 typedef struct MXGContext {
37  unsigned int buffer_size;
38  int64_t dts;
39  unsigned int cache_size;
40 } MXGContext;
41 
43 {
44  AVStream *video_st, *audio_st;
45  MXGContext *mxg = s->priv_data;
46 
47  /* video parameters will be extracted from the compressed bitstream */
48  video_st = avformat_new_stream(s, NULL);
49  if (!video_st)
50  return AVERROR(ENOMEM);
51  video_st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
52  video_st->codec->codec_id = AV_CODEC_ID_MXPEG;
53  avpriv_set_pts_info(video_st, 64, 1, 1000000);
54 
55  audio_st = avformat_new_stream(s, NULL);
56  if (!audio_st)
57  return AVERROR(ENOMEM);
58  audio_st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
59  audio_st->codec->codec_id = AV_CODEC_ID_PCM_ALAW;
60  audio_st->codec->channels = 1;
62  audio_st->codec->sample_rate = 8000;
63  audio_st->codec->bits_per_coded_sample = 8;
64  audio_st->codec->block_align = 1;
65  avpriv_set_pts_info(audio_st, 64, 1, 1000000);
66 
67  mxg->soi_ptr = mxg->buffer_ptr = mxg->buffer = 0;
68  mxg->buffer_size = 0;
69  mxg->dts = AV_NOPTS_VALUE;
70  mxg->cache_size = 0;
71 
72  return 0;
73 }
74 
76 {
77  for (; p < end - 3; p += 4) {
78  uint32_t x = AV_RN32(p);
79 
80  if (x & (~(x+0x01010101)) & 0x80808080) {
81  if (p[0] == 0xff) {
82  return p;
83  } else if (p[1] == 0xff) {
84  return p+1;
85  } else if (p[2] == 0xff) {
86  return p+2;
87  } else if (p[3] == 0xff) {
88  return p+3;
89  }
90  }
91  }
92 
93  for (; p < end; ++p) {
94  if (*p == 0xff) return p;
95  }
96 
97  return end;
98 }
99 
100 static int mxg_update_cache(AVFormatContext *s, unsigned int cache_size)
101 {
102  MXGContext *mxg = s->priv_data;
103  unsigned int current_pos = mxg->buffer_ptr - mxg->buffer;
104  unsigned int soi_pos;
105  uint8_t *buffer;
106  int ret;
107 
108  /* reallocate internal buffer */
109  if (current_pos > current_pos + cache_size)
110  return AVERROR(ENOMEM);
111  soi_pos = mxg->soi_ptr - mxg->buffer;
112  buffer = av_fast_realloc(mxg->buffer, &mxg->buffer_size,
113  current_pos + cache_size +
115  if (!buffer)
116  return AVERROR(ENOMEM);
117  mxg->buffer = buffer;
118  mxg->buffer_ptr = mxg->buffer + current_pos;
119  if (mxg->soi_ptr) mxg->soi_ptr = mxg->buffer + soi_pos;
120 
121  /* get data */
122  ret = avio_read(s->pb, mxg->buffer_ptr + mxg->cache_size,
123  cache_size - mxg->cache_size);
124  if (ret < 0)
125  return ret;
126 
127  mxg->cache_size += ret;
128 
129  return ret;
130 }
131 
133 {
134  int ret;
135  unsigned int size;
136  uint8_t *startmarker_ptr, *end, *search_end, marker;
137  MXGContext *mxg = s->priv_data;
138 
139  while (!url_feof(s->pb) && !s->pb->error){
140  if (mxg->cache_size <= OVERREAD_SIZE) {
141  /* update internal buffer */
143  if (ret < 0)
144  return ret;
145  }
146  end = mxg->buffer_ptr + mxg->cache_size;
147 
148  /* find start marker - 0xff */
149  if (mxg->cache_size > OVERREAD_SIZE) {
150  search_end = end - OVERREAD_SIZE;
151  startmarker_ptr = mxg_find_startmarker(mxg->buffer_ptr, search_end);
152  } else {
153  search_end = end;
154  startmarker_ptr = mxg_find_startmarker(mxg->buffer_ptr, search_end);
155  if (startmarker_ptr >= search_end - 1 ||
156  *(startmarker_ptr + 1) != EOI) break;
157  }
158 
159  if (startmarker_ptr != search_end) { /* start marker found */
160  marker = *(startmarker_ptr + 1);
161  mxg->buffer_ptr = startmarker_ptr + 2;
162  mxg->cache_size = end - mxg->buffer_ptr;
163 
164  if (marker == SOI) {
165  mxg->soi_ptr = startmarker_ptr;
166  } else if (marker == EOI) {
167  if (!mxg->soi_ptr) {
168  av_log(s, AV_LOG_WARNING, "Found EOI before SOI, skipping\n");
169  continue;
170  }
171 
172  pkt->pts = pkt->dts = mxg->dts;
173  pkt->stream_index = 0;
174 #if FF_API_DESTRUCT_PACKET
176  pkt->destruct = NULL;
178 #endif
179  pkt->buf = NULL;
180  pkt->size = mxg->buffer_ptr - mxg->soi_ptr;
181  pkt->data = mxg->soi_ptr;
182 
183  if (mxg->soi_ptr - mxg->buffer > mxg->cache_size) {
184  if (mxg->cache_size > 0) {
185  memcpy(mxg->buffer, mxg->buffer_ptr, mxg->cache_size);
186  }
187 
188  mxg->buffer_ptr = mxg->buffer;
189  }
190  mxg->soi_ptr = 0;
191 
192  return pkt->size;
193  } else if ( (SOF0 <= marker && marker <= SOF15) ||
194  (SOS <= marker && marker <= COM) ) {
195  /* all other markers that start marker segment also contain
196  length value (see specification for JPEG Annex B.1) */
197  size = AV_RB16(mxg->buffer_ptr);
198  if (size < 2)
199  return AVERROR(EINVAL);
200 
201  if (mxg->cache_size < size) {
202  ret = mxg_update_cache(s, size);
203  if (ret < 0)
204  return ret;
205  startmarker_ptr = mxg->buffer_ptr - 2;
206  mxg->cache_size = 0;
207  } else {
208  mxg->cache_size -= size;
209  }
210 
211  mxg->buffer_ptr += size;
212 
213  if (marker == APP13 && size >= 16) { /* audio data */
214  /* time (GMT) of first sample in usec since 1970, little-endian */
215  pkt->pts = pkt->dts = AV_RL64(startmarker_ptr + 8);
216  pkt->stream_index = 1;
217 #if FF_API_DESTRUCT_PACKET
219  pkt->destruct = NULL;
221 #endif
222  pkt->buf = NULL;
223  pkt->size = size - 14;
224  pkt->data = startmarker_ptr + 16;
225 
226  if (startmarker_ptr - mxg->buffer > mxg->cache_size) {
227  if (mxg->cache_size > 0) {
228  memcpy(mxg->buffer, mxg->buffer_ptr, mxg->cache_size);
229  }
230  mxg->buffer_ptr = mxg->buffer;
231  }
232 
233  return pkt->size;
234  } else if (marker == COM && size >= 18 &&
235  !strncmp(startmarker_ptr + 4, "MXF", 3)) {
236  /* time (GMT) of video frame in usec since 1970, little-endian */
237  mxg->dts = AV_RL64(startmarker_ptr + 12);
238  }
239  }
240  } else {
241  /* start marker not found */
242  mxg->buffer_ptr = search_end;
243  mxg->cache_size = OVERREAD_SIZE;
244  }
245  }
246 
247  return AVERROR_EOF;
248 }
249 
250 static int mxg_close(struct AVFormatContext *s)
251 {
252  MXGContext *mxg = s->priv_data;
253  av_freep(&mxg->buffer);
254  return 0;
255 }
256 
258  .name = "mxg",
259  .long_name = NULL_IF_CONFIG_SMALL("MxPEG clip"),
260  .priv_data_size = sizeof(MXGContext),
264  .extensions = "mxg",
265 };