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subfile.c
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1 /*
2  * Copyright (c) 2014 Nicolas George
3  *
4  * This file is part of FFmpeg.
5  *
6  * FFmpeg is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public License
8  * as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * FFmpeg is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14  * GNU Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public License
17  * along with FFmpeg; if not, write to the Free Software Foundation, Inc.,
18  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 #include "libavutil/avassert.h"
22 #include "libavutil/avstring.h"
23 #include "libavutil/opt.h"
24 #include "avformat.h"
25 #include "url.h"
26 
27 typedef struct SubfileContext {
28  const AVClass *class;
30  int64_t start;
31  int64_t end;
32  int64_t pos;
34 
35 #define OFFSET(field) offsetof(SubfileContext, field)
36 #define D AV_OPT_FLAG_DECODING_PARAM
37 
38 static const AVOption subfile_options[] = {
39  { "start", "start offset", OFFSET(start), AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX, D },
40  { "end", "end offset", OFFSET(end), AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX, D },
41  { NULL }
42 };
43 
44 #undef OFFSET
45 #undef D
46 
47 static const AVClass subfile_class = {
48  .class_name = "subfile",
49  .item_name = av_default_item_name,
50  .option = subfile_options,
51  .version = LIBAVUTIL_VERSION_INT,
52 };
53 
54 static int slave_seek(URLContext *h)
55 {
57  int64_t ret;
58 
59  if ((ret = ffurl_seek(c->h, c->pos, SEEK_SET)) != c->pos) {
60  if (ret >= 0)
61  ret = AVERROR_BUG;
62  av_log(h, AV_LOG_ERROR, "Impossible to seek in file: %s\n",
63  av_err2str(ret));
64  return ret;
65  }
66  return 0;
67 }
68 
69 static int subfile_open(URLContext *h, const char *filename, int flags,
71 {
73  int ret;
74 
75  if (c->end <= c->start) {
76  av_log(h, AV_LOG_ERROR, "end before start\n");
77  return AVERROR(EINVAL);
78  }
79  av_strstart(filename, "subfile:", &filename);
80  ret = ffurl_open(&c->h, filename, flags, &h->interrupt_callback, options);
81  if (ret < 0)
82  return ret;
83  c->pos = c->start;
84  if ((ret = slave_seek(h)) < 0) {
85  ffurl_close(c->h);
86  return ret;
87  }
88  return 0;
89 }
90 
91 static int subfile_close(URLContext *h)
92 {
94  return ffurl_close(c->h);
95 }
96 
97 static int subfile_read(URLContext *h, unsigned char *buf, int size)
98 {
100  int64_t rest = c->end - c->pos;
101  int ret;
102 
103  if (rest <= 0)
104  return 0;
105  size = FFMIN(size, rest);
106  ret = ffurl_read(c->h, buf, size);
107  if (ret >= 0)
108  c->pos += ret;
109  return ret;
110 }
111 
112 static int64_t subfile_seek(URLContext *h, int64_t pos, int whence)
113 {
114  SubfileContext *c = h->priv_data;
115  int64_t new_pos = -1;
116  int ret;
117 
118  if (whence == AVSEEK_SIZE)
119  return c->end - c->start;
120  switch (whence) {
121  case SEEK_SET:
122  new_pos = c->start + pos;
123  break;
124  case SEEK_CUR:
125  new_pos += pos;
126  break;
127  case SEEK_END:
128  new_pos = c->end + c->pos;
129  break;
130  }
131  if (new_pos < c->start)
132  return AVERROR(EINVAL);
133  c->pos = new_pos;
134  if ((ret = slave_seek(h)) < 0)
135  return ret;
136  return c->pos - c->start;
137 }
138 
140  .name = "subfile",
141  .url_open2 = subfile_open,
142  .url_read = subfile_read,
143  .url_seek = subfile_seek,
144  .url_close = subfile_close,
145  .priv_data_size = sizeof(SubfileContext),
146  .priv_data_class = &subfile_class,
147 };