seek.c
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1 /*
2  * seek utility functions for use within format handlers
3  *
4  * Copyright (c) 2009 Ivan Schreter
5  *
6  * This file is part of Libav.
7  *
8  * Libav is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * Libav is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with Libav; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 #include "seek.h"
24 #include "libavutil/mathematics.h"
25 #include "libavutil/mem.h"
26 #include "internal.h"
27 
28 // NOTE: implementation should be moved here in another patch, to keep patches
29 // separated.
30 
34 typedef struct {
35  int64_t pos_lo;
36  int64_t ts_lo;
37 
38  int64_t pos_hi;
39  int64_t ts_hi;
40 
41  int64_t last_pos;
42 
43  int64_t term_ts;
45  int64_t first_ts;
47 
48  int terminated;
49 } AVSyncPoint;
50 
63 static int64_t ts_distance(int64_t ts_hi,
64  AVRational tb_hi,
65  int64_t ts_lo,
66  AVRational tb_lo)
67 {
68  int64_t hi, lo;
69 
70  hi = ts_hi * tb_hi.num * tb_lo.den;
71  lo = ts_lo * tb_lo.num * tb_hi.den;
72 
73  return hi - lo;
74 }
75 
98  int64_t timestamp,
99  AVRational timebase,
100  int flags,
101  AVSyncPoint *sync,
102  int keyframes_to_find,
103  int *found_lo,
104  int *found_hi,
105  int first_iter)
106 {
107  AVPacket pkt;
108  AVSyncPoint *sp;
109  AVStream *st;
110  int idx;
111  int flg;
112  int terminated_count = 0;
113  int64_t pos;
114  int64_t pts, dts; // PTS/DTS from stream
115  int64_t ts; // PTS in stream-local time base or position for byte seeking
116  AVRational ts_tb; // Time base of the stream or 1:1 for byte seeking
117 
118  for (;;) {
119  if (av_read_frame(s, &pkt) < 0) {
120  // EOF or error, make sure high flags are set
121  for (idx = 0; idx < s->nb_streams; ++idx) {
122  if (s->streams[idx]->discard < AVDISCARD_ALL) {
123  sp = &sync[idx];
124  if (sp->pos_hi == INT64_MAX) {
125  // no high frame exists for this stream
126  (*found_hi)++;
127  sp->ts_hi = INT64_MAX;
128  sp->pos_hi = INT64_MAX - 1;
129  }
130  }
131  }
132  break;
133  }
134 
135  idx = pkt.stream_index;
136  st = s->streams[idx];
137  if (st->discard >= AVDISCARD_ALL)
138  // this stream is not active, skip packet
139  continue;
140 
141  sp = &sync[idx];
142 
143  flg = pkt.flags;
144  pos = pkt.pos;
145  pts = pkt.pts;
146  dts = pkt.dts;
147  if (pts == AV_NOPTS_VALUE)
148  // some formats don't provide PTS, only DTS
149  pts = dts;
150 
151  av_free_packet(&pkt);
152 
153  // Multi-frame packets only return position for the very first frame.
154  // Other frames are read with position == -1. Therefore, we note down
155  // last known position of a frame and use it if a frame without
156  // position arrives. In this way, it's possible to seek to proper
157  // position. Additionally, for parsers not providing position at all,
158  // an approximation will be used (starting position of this iteration).
159  if (pos < 0)
160  pos = sp->last_pos;
161  else
162  sp->last_pos = pos;
163 
164  // Evaluate key frames with known TS (or any frames, if AVSEEK_FLAG_ANY set).
165  if (pts != AV_NOPTS_VALUE &&
166  ((flg & AV_PKT_FLAG_KEY) || (flags & AVSEEK_FLAG_ANY))) {
167  if (flags & AVSEEK_FLAG_BYTE) {
168  // for byte seeking, use position as timestamp
169  ts = pos;
170  ts_tb.num = 1;
171  ts_tb.den = 1;
172  } else {
173  // otherwise, get stream time_base
174  ts = pts;
175  ts_tb = st->time_base;
176  }
177 
178  if (sp->first_ts == AV_NOPTS_VALUE) {
179  // Note down termination timestamp for the next iteration - when
180  // we encounter a packet with the same timestamp, we will ignore
181  // any further packets for this stream in next iteration (as they
182  // are already evaluated).
183  sp->first_ts = ts;
184  sp->first_ts_tb = ts_tb;
185  }
186 
187  if (sp->term_ts != AV_NOPTS_VALUE &&
188  av_compare_ts(ts, ts_tb, sp->term_ts, sp->term_ts_tb) > 0) {
189  // past the end position from last iteration, ignore packet
190  if (!sp->terminated) {
191  sp->terminated = 1;
192  ++terminated_count;
193  if (sp->pos_hi == INT64_MAX) {
194  // no high frame exists for this stream
195  (*found_hi)++;
196  sp->ts_hi = INT64_MAX;
197  sp->pos_hi = INT64_MAX - 1;
198  }
199  if (terminated_count == keyframes_to_find)
200  break; // all terminated, iteration done
201  }
202  continue;
203  }
204 
205  if (av_compare_ts(ts, ts_tb, timestamp, timebase) <= 0) {
206  // keyframe found before target timestamp
207  if (sp->pos_lo == INT64_MAX) {
208  // found first keyframe lower than target timestamp
209  (*found_lo)++;
210  sp->ts_lo = ts;
211  sp->pos_lo = pos;
212  } else if (sp->ts_lo < ts) {
213  // found a better match (closer to target timestamp)
214  sp->ts_lo = ts;
215  sp->pos_lo = pos;
216  }
217  }
218  if (av_compare_ts(ts, ts_tb, timestamp, timebase) >= 0) {
219  // keyframe found after target timestamp
220  if (sp->pos_hi == INT64_MAX) {
221  // found first keyframe higher than target timestamp
222  (*found_hi)++;
223  sp->ts_hi = ts;
224  sp->pos_hi = pos;
225  if (*found_hi >= keyframes_to_find && first_iter) {
226  // We found high frame for all. They may get updated
227  // to TS closer to target TS in later iterations (which
228  // will stop at start position of previous iteration).
229  break;
230  }
231  } else if (sp->ts_hi > ts) {
232  // found a better match (actually, shouldn't happen)
233  sp->ts_hi = ts;
234  sp->pos_hi = pos;
235  }
236  }
237  }
238  }
239 
240  // Clean up the parser.
242 }
243 
245  int stream_index,
246  int64_t pos,
247  int64_t ts_min,
248  int64_t ts,
249  int64_t ts_max,
250  int flags)
251 {
252  AVSyncPoint *sync, *sp;
253  AVStream *st;
254  int i;
255  int keyframes_to_find = 0;
256  int64_t curpos;
257  int64_t step;
258  int found_lo = 0, found_hi = 0;
259  int64_t min_distance, distance;
260  int64_t min_pos = 0;
261  int first_iter = 1;
262  AVRational time_base;
263 
264  if (flags & AVSEEK_FLAG_BYTE) {
265  // for byte seeking, we have exact 1:1 "timestamps" - positions
266  time_base.num = 1;
267  time_base.den = 1;
268  } else {
269  if (stream_index >= 0) {
270  // we have a reference stream, which time base we use
271  st = s->streams[stream_index];
272  time_base = st->time_base;
273  } else {
274  // no reference stream, use AV_TIME_BASE as reference time base
275  time_base.num = 1;
276  time_base.den = AV_TIME_BASE;
277  }
278  }
279 
280  // Initialize syncpoint structures for each stream.
281  sync = av_malloc(s->nb_streams * sizeof(AVSyncPoint));
282  if (!sync)
283  // cannot allocate helper structure
284  return -1;
285 
286  for (i = 0; i < s->nb_streams; ++i) {
287  st = s->streams[i];
288  sp = &sync[i];
289 
290  sp->pos_lo = INT64_MAX;
291  sp->ts_lo = INT64_MAX;
292  sp->pos_hi = INT64_MAX;
293  sp->ts_hi = INT64_MAX;
294  sp->terminated = 0;
295  sp->first_ts = AV_NOPTS_VALUE;
296  sp->term_ts = ts_max;
297  sp->term_ts_tb = time_base;
298  sp->last_pos = pos;
299 
300  st->cur_dts = AV_NOPTS_VALUE;
301 
302  if (st->discard < AVDISCARD_ALL)
303  ++keyframes_to_find;
304  }
305 
306  if (!keyframes_to_find) {
307  // no stream active, error
308  av_free(sync);
309  return -1;
310  }
311 
312  // Find keyframes in all active streams with timestamp/position just before
313  // and just after requested timestamp/position.
314  step = s->pb->buffer_size;
315  curpos = FFMAX(pos - step / 2, 0);
316  for (;;) {
317  avio_seek(s->pb, curpos, SEEK_SET);
319  ts, time_base,
320  flags,
321  sync,
322  keyframes_to_find,
323  &found_lo, &found_hi,
324  first_iter);
325  if (found_lo == keyframes_to_find && found_hi == keyframes_to_find)
326  break; // have all keyframes we wanted
327  if (!curpos)
328  break; // cannot go back anymore
329 
330  curpos = pos - step;
331  if (curpos < 0)
332  curpos = 0;
333  step *= 2;
334 
335  // switch termination positions
336  for (i = 0; i < s->nb_streams; ++i) {
337  st = s->streams[i];
338  st->cur_dts = AV_NOPTS_VALUE;
339 
340  sp = &sync[i];
341  if (sp->first_ts != AV_NOPTS_VALUE) {
342  sp->term_ts = sp->first_ts;
343  sp->term_ts_tb = sp->first_ts_tb;
344  sp->first_ts = AV_NOPTS_VALUE;
345  }
346  sp->terminated = 0;
347  sp->last_pos = curpos;
348  }
349  first_iter = 0;
350  }
351 
352  // Find actual position to start decoding so that decoder synchronizes
353  // closest to ts and between ts_min and ts_max.
354  pos = INT64_MAX;
355 
356  for (i = 0; i < s->nb_streams; ++i) {
357  st = s->streams[i];
358  if (st->discard < AVDISCARD_ALL) {
359  sp = &sync[i];
360  min_distance = INT64_MAX;
361  // Find timestamp closest to requested timestamp within min/max limits.
362  if (sp->pos_lo != INT64_MAX
363  && av_compare_ts(ts_min, time_base, sp->ts_lo, st->time_base) <= 0
364  && av_compare_ts(sp->ts_lo, st->time_base, ts_max, time_base) <= 0) {
365  // low timestamp is in range
366  min_distance = ts_distance(ts, time_base, sp->ts_lo, st->time_base);
367  min_pos = sp->pos_lo;
368  }
369  if (sp->pos_hi != INT64_MAX
370  && av_compare_ts(ts_min, time_base, sp->ts_hi, st->time_base) <= 0
371  && av_compare_ts(sp->ts_hi, st->time_base, ts_max, time_base) <= 0) {
372  // high timestamp is in range, check distance
373  distance = ts_distance(sp->ts_hi, st->time_base, ts, time_base);
374  if (distance < min_distance) {
375  min_distance = distance;
376  min_pos = sp->pos_hi;
377  }
378  }
379  if (min_distance == INT64_MAX) {
380  // no timestamp is in range, cannot seek
381  av_free(sync);
382  return -1;
383  }
384  if (min_pos < pos)
385  pos = min_pos;
386  }
387  }
388 
389  avio_seek(s->pb, pos, SEEK_SET);
390  av_free(sync);
391  return pos;
392 }
393 
395 {
396  int i;
397  AVStream *st;
400  if (!state)
401  return NULL;
402 
403  state->stream_states = av_malloc(sizeof(AVParserStreamState) * s->nb_streams);
404  if (!state->stream_states) {
405  av_free(state);
406  return NULL;
407  }
408 
409  state->fpos = avio_tell(s->pb);
410 
411  // copy context structures
412  state->packet_buffer = s->packet_buffer;
413  state->parse_queue = s->parse_queue;
416 
417  s->packet_buffer = NULL;
418  s->parse_queue = NULL;
419  s->raw_packet_buffer = NULL;
421 
422  // copy stream structures
423  state->nb_streams = s->nb_streams;
424  for (i = 0; i < s->nb_streams; i++) {
425  st = s->streams[i];
426  ss = &state->stream_states[i];
427 
428  ss->parser = st->parser;
429  ss->last_IP_pts = st->last_IP_pts;
430  ss->cur_dts = st->cur_dts;
431  ss->reference_dts = st->reference_dts;
432  ss->probe_packets = st->probe_packets;
433 
434  st->parser = NULL;
436  st->cur_dts = AV_NOPTS_VALUE;
439  }
440 
441  return state;
442 }
443 
445 {
446  int i;
447  AVStream *st;
450 
451  if (!state)
452  return;
453 
454  avio_seek(s->pb, state->fpos, SEEK_SET);
455 
456  // copy context structures
457  s->packet_buffer = state->packet_buffer;
458  s->parse_queue = state->parse_queue;
461 
462  // copy stream structures
463  for (i = 0; i < state->nb_streams; i++) {
464  st = s->streams[i];
465  ss = &state->stream_states[i];
466 
467  st->parser = ss->parser;
468  st->last_IP_pts = ss->last_IP_pts;
469  st->cur_dts = ss->cur_dts;
470  st->reference_dts = ss->reference_dts;
471  st->probe_packets = ss->probe_packets;
472  }
473 
474  av_free(state->stream_states);
475  av_free(state);
476 }
477 
478 static void free_packet_list(AVPacketList *pktl)
479 {
480  AVPacketList *cur;
481  while (pktl) {
482  cur = pktl;
483  pktl = cur->next;
484  av_free_packet(&cur->pkt);
485  av_free(cur);
486  }
487 }
488 
490 {
491  int i;
493 
494  if (!state)
495  return;
496 
497  for (i = 0; i < state->nb_streams; i++) {
498  ss = &state->stream_states[i];
499  if (ss->parser)
500  av_parser_close(ss->parser);
501  }
502 
506 
507  av_free(state->stream_states);
508  av_free(state);
509 }
int64_t cur_dts
Definition: seek.h:35
void * av_malloc(size_t size)
Allocate a block of size bytes with alignment suitable for all memory accesses (including vectors if ...
Definition: mem.c:61
AVParserState * ff_store_parser_state(AVFormatContext *s)
Store current parser state and file position.
Definition: seek.c:394
void av_free_packet(AVPacket *pkt)
Free a packet.
Definition: avpacket.c:153
AVRational first_ts_tb
timebase for first_ts
Definition: seek.c:46
memory handling functions
int64_t pos
byte position in stream, -1 if unknown
Definition: avcodec.h:940
int probe_packets
Definition: avformat.h:767
int64_t ts_lo
frame presentation timestamp or same as pos_lo for byte seeking
Definition: seek.c:36
int num
numerator
Definition: rational.h:44
int64_t avio_seek(AVIOContext *s, int64_t offset, int whence)
fseek() equivalent for AVIOContext.
Definition: aviobuf.c:186
static int sync(AVFormatContext *s, uint8_t *header)
Read input until we find the next ident.
Definition: lxfdec.c:84
discard all
Definition: avcodec.h:536
int64_t last_IP_pts
Definition: seek.h:34
static void search_hi_lo_keyframes(AVFormatContext *s, int64_t timestamp, AVRational timebase, int flags, AVSyncPoint *sync, int keyframes_to_find, int *found_lo, int *found_hi, int first_iter)
Partial search for keyframes in multiple streams.
Definition: seek.c:97
AVPacketList * raw_packet_buffer
raw packet buffer of original state
Definition: seek.h:49
struct AVPacketList * packet_buffer
This buffer is only needed when packets were already buffered but not decoded, for example to get the...
Definition: avformat.h:1025
int64_t pos_lo
position of the frame with low timestamp in file or INT64_MAX if not found (yet)
Definition: seek.c:35
Format I/O context.
Definition: avformat.h:828
int64_t cur_dts
Definition: avformat.h:759
void ff_read_frame_flush(AVFormatContext *s)
Flush the frame reader.
Definition: utils.c:1295
AVParserStreamState * stream_states
states of individual streams (array)
Definition: seek.h:54
AVPacket pkt
Definition: avformat.h:1052
AVStream ** streams
Definition: avformat.h:876
static int flags
Definition: log.c:42
#define sp
Definition: regdef.h:63
static av_always_inline int64_t avio_tell(AVIOContext *s)
ftell() equivalent for AVIOContext.
Definition: avio.h:219
int64_t term_ts
termination timestamp (which TS we already read)
Definition: seek.c:43
struct AVPacketList * raw_packet_buffer
Raw packets from the demuxer, prior to parsing and decoding.
Definition: avformat.h:1037
void av_free(void *ptr)
Free a memory block which has been allocated with av_malloc(z)() or av_realloc(). ...
Definition: mem.c:139
AVRational term_ts_tb
timebase for term_ts
Definition: seek.c:44
structure to store parser state of one AVStream
Definition: seek.h:31
void ff_restore_parser_state(AVFormatContext *s, AVParserState *state)
Restore previously saved parser state and file position.
Definition: seek.c:444
helper structure describing keyframe search state of one stream
Definition: seek.c:34
int flags
A combination of AV_PKT_FLAG values.
Definition: avcodec.h:921
int av_compare_ts(int64_t ts_a, AVRational tb_a, int64_t ts_b, AVRational tb_b)
Compare 2 timestamps each in its own timebases.
Definition: mathematics.c:127
static float distance(float x, float y, int band)
unsigned int nb_streams
A list of all streams in the file.
Definition: avformat.h:875
int64_t ts_hi
frame presentation timestamp or same as pos_hi for byte seeking
Definition: seek.c:39
structure to store parser state of AVFormat
Definition: seek.h:43
void av_parser_close(AVCodecParserContext *s)
Definition: parser.c:203
int terminated
termination flag for the current iteration
Definition: seek.c:48
int64_t first_ts
first packet timestamp in this iteration (to fill term_ts later)
Definition: seek.c:45
int buffer_size
Maximum buffer size.
Definition: avio.h:83
int64_t last_pos
last known position of a frame, for multi-frame packets
Definition: seek.c:41
int raw_packet_buffer_remaining_size
Definition: avformat.h:1048
Stream structure.
Definition: avformat.h:622
int64_t reference_dts
Definition: seek.h:36
NULL
Definition: eval.c:52
AVIOContext * pb
I/O context.
Definition: avformat.h:861
int64_t reference_dts
Timestamp corresponding to the last dts sync point.
Definition: avformat.h:757
AVPacketList * parse_queue
parse queue of original state
Definition: seek.h:48
rational number numerator/denominator
Definition: rational.h:43
static int step
Definition: avplay.c:252
int av_read_frame(AVFormatContext *s, AVPacket *pkt)
Return the next frame of a stream.
Definition: utils.c:1206
int nb_streams
number of streams with stored state
Definition: seek.h:53
static uint32_t state
Definition: trasher.c:27
struct AVPacketList * parse_queue
Packets split by the parser get queued here.
Definition: avformat.h:1042
static void free_packet_list(AVPacketList *pktl)
Definition: seek.c:478
AVCodecParserContext * parser
Definition: seek.h:33
int64_t ff_gen_syncpoint_search(AVFormatContext *s, int stream_index, int64_t pos, int64_t ts_min, int64_t ts, int64_t ts_max, int flags)
Search for the sync point of all active streams.
Definition: seek.c:244
struct AVPacketList * next
Definition: avformat.h:1053
int64_t fpos
file position at the time of call
Definition: seek.h:44
void ff_free_parser_state(AVFormatContext *s, AVParserState *state)
Free previously saved parser state.
Definition: seek.c:489
int raw_packet_buffer_remaining_size
remaining space in raw_packet_buffer
Definition: seek.h:50
int den
denominator
Definition: rational.h:45
static int64_t ts_distance(int64_t ts_hi, AVRational tb_hi, int64_t ts_lo, AVRational tb_lo)
Compute a distance between timestamps.
Definition: seek.c:63
struct AVCodecParserContext * parser
Definition: avformat.h:776
AVPacketList * packet_buffer
packet buffer of original state
Definition: seek.h:47
int probe_packets
Definition: seek.h:37
int64_t dts
Decompression timestamp in AVStream->time_base units; the time at which the packet is decompressed...
Definition: avcodec.h:914
int64_t last_IP_pts
Definition: avformat.h:760
int stream_index
Definition: avcodec.h:917
AVRational time_base
This is the fundamental unit of time (in seconds) in terms of which frame timestamps are represented...
Definition: avformat.h:669
enum AVDiscard discard
Selects which packets can be discarded at will and do not need to be demuxed.
Definition: avformat.h:690
This structure stores compressed data.
Definition: avcodec.h:898
int64_t pts
Presentation timestamp in AVStream->time_base units; the time at which the decompressed packet will b...
Definition: avcodec.h:908
int64_t pos_hi
position of the frame with high timestamp in file or INT64_MAX if not found (yet) ...
Definition: seek.c:38