[FFmpeg-cvslog] r19680 - in trunk/libavformat: Makefile seek.c seek.h utils.c
schreter
subversion
Sat Aug 22 18:05:44 CEST 2009
Author: schreter
Date: Sat Aug 22 18:05:43 2009
New Revision: 19680
Log:
Support for generic multi-stream key frame finding for new seek API.
Added:
trunk/libavformat/seek.c
trunk/libavformat/seek.h
Modified:
trunk/libavformat/Makefile
trunk/libavformat/utils.c
Modified: trunk/libavformat/Makefile
==============================================================================
--- trunk/libavformat/Makefile Sat Aug 22 17:56:06 2009 (r19679)
+++ trunk/libavformat/Makefile Sat Aug 22 18:05:43 2009 (r19680)
@@ -5,7 +5,7 @@ FFLIBS = avcodec avutil
HEADERS = avformat.h avio.h
-OBJS = allformats.o cutils.o metadata.o metadata_compat.o options.o os_support.o sdp.o utils.o
+OBJS = allformats.o cutils.o metadata.o metadata_compat.o options.o os_support.o sdp.o seek.o utils.o
# muxers/demuxers
OBJS-$(CONFIG_AAC_DEMUXER) += raw.o id3v1.o id3v2.o
Added: trunk/libavformat/seek.c
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ trunk/libavformat/seek.c Sat Aug 22 18:05:43 2009 (r19680)
@@ -0,0 +1,578 @@
+/*
+ * Utility functions for seeking for use within FFmpeg format handlers.
+ *
+ * Copyright (c) 2009 Ivan Schreter
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "seek.h"
+#include "libavutil/mem.h"
+
+// NOTE: implementation should be moved here in another patch, to keep patches
+// separated.
+extern void av_read_frame_flush(AVFormatContext *s);
+
+/**
+ * Helper structure to store parser state of AVStream.
+ */
+typedef struct AVStreamState {
+ // Saved members of AVStream
+ AVCodecParserContext *parser;
+ AVPacket cur_pkt;
+ int64_t last_IP_pts;
+ int64_t cur_dts;
+ int64_t reference_dts;
+ const uint8_t *cur_ptr;
+ int cur_len;
+ int probe_packets;
+} AVStreamState;
+
+/**
+ * Helper structure to store parser state of AVFormat.
+ */
+struct AVParserState {
+ int64_t fpos; ///< File position at the time of call.
+
+ // Saved members of AVFormatContext
+ AVStream *cur_st; ///< Current stream.
+ AVPacketList *packet_buffer; ///< Packet buffer of original state.
+ AVPacketList *raw_packet_buffer; ///< Raw packet buffer of original state.
+ int raw_packet_buffer_remaining_size; ///< Remaining size available for raw_packet_buffer.
+
+ // Saved info for streams.
+ int nb_streams; ///< Number of streams with stored state.
+ AVStreamState *stream_states; ///< States of individual streams (array).
+};
+
+/**
+ * Helper structure describing keyframe search state of one stream.
+ */
+typedef struct {
+ int64_t pos_lo; ///< Position of the frame with low timestamp in file or INT64_MAX if not found (yet).
+ int64_t ts_lo; ///< Frame presentation timestamp or same as pos_lo for byte seeking.
+
+ int64_t pos_hi; ///< Position of the frame with high timestamp in file or INT64_MAX if not found (yet).
+ int64_t ts_hi; ///< Frame presentation timestamp or same as pos_hi for byte seeking.
+
+ int64_t last_pos; ///< Last known position of a frame, for multi-frame packets.
+
+ int64_t term_ts; ///< Termination timestamp (which TS we already read).
+ AVRational term_ts_tb; ///< Timebase for term_ts.
+ int64_t first_ts; ///< First packet timestamp in this iteration (to fill term_ts later).
+ AVRational first_ts_tb;///< Timebase for first_ts.
+
+ int terminated; ///< Termination flag for current iteration.
+} AVSyncPoint;
+
+/**
+ * Compare two timestamps exactly, taking into account their respective time bases.
+ *
+ * @param ts_a timestamp A.
+ * @param tb_a time base for timestamp A.
+ * @param ts_b timestamp B.
+ * @param tb_b time base for timestamp A.
+ * @return -1. 0 or 1 if timestamp A is less than, equal or greater than timestamp B.
+ */
+static int compare_ts(int64_t ts_a, AVRational tb_a, int64_t ts_b, AVRational tb_b)
+{
+ int64_t a, b, res;
+
+ if (ts_a == INT64_MIN)
+ return ts_a < ts_b ? -1 : 0;
+ if (ts_a == INT64_MAX)
+ return ts_a > ts_b ? 1 : 0;
+ if (ts_b == INT64_MIN)
+ return ts_a > ts_b ? 1 : 0;
+ if (ts_b == INT64_MAX)
+ return ts_a < ts_b ? -1 : 0;
+
+ a = ts_a * tb_a.num * tb_b.den;
+ b = ts_b * tb_b.num * tb_a.den;
+
+ res = a - b;
+ if (res == 0)
+ return 0;
+ else
+ return (res >> 63) | 1;
+}
+
+/**
+ * Compute a distance between timestamps.
+ *
+ * Distances are only comparable, if same time bases are used for computing
+ * distances.
+ *
+ * @param ts_hi high timestamp.
+ * @param tb_hi high timestamp time base.
+ * @param ts_lo low timestamp.
+ * @param tb_lo low timestamp time base.
+ * @return representation of distance between high and low timestamps.
+ */
+static int64_t ts_distance(int64_t ts_hi, AVRational tb_hi, int64_t ts_lo, AVRational tb_lo)
+{
+ int64_t hi, lo;
+
+ hi = ts_hi * tb_hi.num * tb_lo.den;
+ lo = ts_lo * tb_lo.num * tb_hi.den;
+
+ return hi - lo;
+}
+
+/**
+ * Partial search for keyframes in multiple streams.
+ *
+ * This routine searches for the next lower and next higher timestamp to
+ * given target timestamp in each stream, starting at current file position
+ * and ending at position, where all streams have already been examined
+ * (or when all higher key frames found in first iteration).
+ *
+ * This routine is called iteratively with exponential backoff to find lower
+ * timestamp.
+ *
+ * @param s format context.
+ * @param timestamp target timestamp (or position, if AVSEEK_FLAG_BYTE).
+ * @param timebase time base for timestamps.
+ * @param flags seeking flags.
+ * @param sync array with information per stream.
+ * @param keyframes_to_find count of keyframes to find in total.
+ * @param found_lo pointer to count of already found low timestamp keyframes.
+ * @param found_hi pointer to count of already found high timestamp keyframes.
+ * @param first_iter flag for first iteration.
+ */
+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)
+{
+ AVPacket pkt;
+ AVSyncPoint *sp;
+ AVStream *st;
+ int idx;
+ int flg;
+ int terminated_count = 0;
+ int64_t pos;
+ int64_t pts, dts; // PTS/DTS from stream
+ int64_t ts; // PTS in stream-local time base or position for byte seeking
+ AVRational ts_tb; // Time base of the stream or 1:1 for byte seeking
+
+ for (;;) {
+ if (av_read_frame(s, &pkt) < 0) {
+ // EOF or error, make sure high flags are set
+ for (idx = 0; idx < s->nb_streams; ++idx) {
+ if (s->streams[idx]->discard < AVDISCARD_ALL) {
+ sp = &sync[idx];
+ if (sp->pos_hi == INT64_MAX) {
+ // No high frame exists for this stream
+ (*found_hi)++;
+ sp->ts_hi = INT64_MAX;
+ sp->pos_hi = INT64_MAX - 1;
+ }
+ }
+ }
+ break;
+ }
+
+ idx = pkt.stream_index;
+ st = s->streams[idx];
+ if (st->discard >= AVDISCARD_ALL) {
+ // This stream is not active, skip packet.
+ continue;
+ }
+ sp = &sync[idx];
+
+ flg = pkt.flags;
+ pos = pkt.pos;
+ pts = pkt.pts;
+ dts = pkt.dts;
+ if (pts == AV_NOPTS_VALUE) {
+ // Some formats don't provide PTS, only DTS.
+ pts = dts;
+ }
+ av_free_packet(&pkt);
+
+ // Multi-frame packets only return position for the very first frame.
+ // Other frames are read with position == -1. Therefore, we note down
+ // last known position of a frame and use it if a frame without
+ // position arrives. In this way, it's possible to seek to proper
+ // position. Additionally, for parsers not providing position at all,
+ // an approximation will be used (starting position of this iteration).
+ if (pos < 0) {
+ pos = sp->last_pos;
+ } else {
+ sp->last_pos = pos;
+ }
+
+ // Evaluate key frames with known TS (or any frames, if AVSEEK_FLAG_ANY set).
+ if (pts != AV_NOPTS_VALUE && ((flg & PKT_FLAG_KEY) || (flags & AVSEEK_FLAG_ANY))) {
+ if (flags & AVSEEK_FLAG_BYTE) {
+ // For byte seeking, use position as timestamp.
+ ts = pos;
+ ts_tb.num = 1;
+ ts_tb.den = 1;
+ } else {
+ // Get stream time_base.
+ ts = pts;
+ ts_tb = st->time_base;
+ }
+
+ if (sp->first_ts == AV_NOPTS_VALUE) {
+ // Note down termination timestamp for the next iteration - when
+ // we encounter a packet with the same timestamp, we will ignore
+ // any further packets for this stream in next iteration (as they
+ // are already evaluated).
+ sp->first_ts = ts;
+ sp->first_ts_tb = ts_tb;
+ }
+
+ if (sp->term_ts != AV_NOPTS_VALUE && compare_ts(ts, ts_tb, sp->term_ts, sp->term_ts_tb) > 0) {
+ // We are past the end position from last iteration, ignore packet.
+ if (!sp->terminated) {
+ sp->terminated = 1;
+ ++terminated_count;
+ if (sp->pos_hi == INT64_MAX) {
+ // No high frame exists for this stream
+ (*found_hi)++;
+ sp->ts_hi = INT64_MAX;
+ sp->pos_hi = INT64_MAX - 1;
+ }
+ if (terminated_count == keyframes_to_find)
+ break; // all terminated, iteration done
+ }
+ continue;
+ }
+
+ if (compare_ts(ts, ts_tb, timestamp, timebase) <= 0) {
+ // Keyframe found before target timestamp.
+ if (sp->pos_lo == INT64_MAX) {
+ // Found first keyframe lower than target timestamp.
+ (*found_lo)++;
+ sp->ts_lo = ts;
+ sp->pos_lo = pos;
+ } else if (sp->ts_lo < ts) {
+ // Found a better match (closer to target timestamp).
+ sp->ts_lo = ts;
+ sp->pos_lo = pos;
+ }
+ }
+ if (compare_ts(ts, ts_tb, timestamp, timebase) >= 0) {
+ // Keyframe found after target timestamp.
+ if (sp->pos_hi == INT64_MAX) {
+ // Found first keyframe higher than target timestamp.
+ (*found_hi)++;
+ sp->ts_hi = ts;
+ sp->pos_hi = pos;
+ if (*found_hi >= keyframes_to_find && first_iter) {
+ // We found high frame for all. They may get updated
+ // to TS closer to target TS in later iterations (which
+ // will stop at start position of previous iteration).
+ break;
+ }
+ } else if (sp->ts_hi > ts) {
+ // Found a better match (actually, shouldn't happen).
+ sp->ts_hi = ts;
+ sp->pos_hi = pos;
+ }
+ }
+ }
+ }
+
+ // Clean up the parser.
+ av_read_frame_flush(s);
+}
+
+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)
+{
+ AVSyncPoint *sync, *sp;
+ AVStream *st;
+ int i;
+ int keyframes_to_find = 0;
+ int64_t curpos;
+ int64_t step;
+ int found_lo = 0, found_hi = 0;
+ int64_t min_distance, distance;
+ int64_t min_pos = 0;
+ int first_iter = 1;
+ AVRational time_base;
+
+ if (flags & AVSEEK_FLAG_BYTE) {
+ /* For byte seeking, we have exact 1:1 "timestamps" - positions */
+ time_base.num = 1;
+ time_base.den = 1;
+ } else {
+ if (stream_index >= 0) {
+ /* We have a reference stream, which time base we use */
+ st = s->streams[stream_index];
+ time_base = st->time_base;
+ } else {
+ /* No reference stream, use AV_TIME_BASE as reference time base */
+ time_base.num = 1;
+ time_base.den = AV_TIME_BASE;
+ }
+ }
+
+ // Initialize syncpoint structures for each stream.
+ sync = (AVSyncPoint*) av_malloc(s->nb_streams * sizeof(AVSyncPoint));
+ if (!sync) {
+ // cannot allocate helper structure
+ return -1;
+ }
+ for (i = 0; i < s->nb_streams; ++i) {
+ st = s->streams[i];
+ sp = &sync[i];
+
+ sp->pos_lo = INT64_MAX;
+ sp->ts_lo = INT64_MAX;
+ sp->pos_hi = INT64_MAX;
+ sp->ts_hi = INT64_MAX;
+ sp->terminated = 0;
+ sp->first_ts = AV_NOPTS_VALUE;
+ sp->term_ts = ts_max;
+ sp->term_ts_tb = time_base;
+ sp->last_pos = pos;
+
+ st->cur_dts = AV_NOPTS_VALUE;
+
+ if (st->discard < AVDISCARD_ALL)
+ ++keyframes_to_find;
+ }
+
+ if (keyframes_to_find == 0) {
+ // No stream active, error.
+ av_free(sync);
+ return -1;
+ }
+
+ // Find keyframes in all active streams with timestamp/position just before
+ // and just after requested timestamp/position.
+ step = 1024;
+ curpos = pos;
+ for (;;) {
+ url_fseek(s->pb, curpos, SEEK_SET);
+ search_hi_lo_keyframes(s,
+ ts, time_base,
+ flags,
+ sync,
+ keyframes_to_find,
+ &found_lo, &found_hi,
+ first_iter);
+ if (found_lo == keyframes_to_find && found_hi == keyframes_to_find)
+ break; // have all keyframes we wanted
+ if (curpos == 0)
+ break; // cannot go back anymore
+
+ curpos = pos - step;
+ if (curpos < 0)
+ curpos = 0;
+ step *= 2;
+
+ // switch termination positions
+ for (i = 0; i < s->nb_streams; ++i) {
+ st = s->streams[i];
+ st->cur_dts = AV_NOPTS_VALUE;
+
+ sp = &sync[i];
+ if (sp->first_ts != AV_NOPTS_VALUE) {
+ sp->term_ts = sp->first_ts;
+ sp->term_ts_tb = sp->first_ts_tb;
+ sp->first_ts = AV_NOPTS_VALUE;
+ }
+ sp->terminated = 0;
+ sp->last_pos = curpos;
+ }
+ first_iter = 0;
+ }
+
+ // Find actual position to start decoding so that decoder synchronizes
+ // closest to ts and between ts_min and ts_max.
+ pos = INT64_MAX;
+
+ for (i = 0; i < s->nb_streams; ++i) {
+ st = s->streams[i];
+ if (st->discard < AVDISCARD_ALL) {
+ sp = &sync[i];
+ min_distance = INT64_MAX;
+ // Find timestamp closest to requested timestamp within min/max limits.
+ if (sp->pos_lo != INT64_MAX
+ && compare_ts(ts_min, time_base, sp->ts_lo, st->time_base) <= 0
+ && compare_ts(sp->ts_lo, st->time_base, ts_max, time_base) <= 0) {
+ // low timestamp is in range
+ min_distance = ts_distance(ts, time_base, sp->ts_lo, st->time_base);
+ min_pos = sp->pos_lo;
+ }
+ if (sp->pos_hi != INT64_MAX
+ && compare_ts(ts_min, time_base, sp->ts_hi, st->time_base) <= 0
+ && compare_ts(sp->ts_hi, st->time_base, ts_max, time_base) <= 0) {
+ // high timestamp is in range, check distance
+ distance = ts_distance(sp->ts_hi, st->time_base, ts, time_base);
+ if (distance < min_distance) {
+ min_distance = distance;
+ min_pos = sp->pos_hi;
+ }
+ }
+ if (min_distance == INT64_MAX) {
+ // no timestamp is in range, cannot seek
+ av_free(sync);
+ return -1;
+ }
+ if (min_pos < pos)
+ pos = min_pos;
+ }
+ }
+
+ url_fseek(s->pb, pos, SEEK_SET);
+ av_free(sync);
+ return pos;
+}
+
+AVParserState *ff_store_parser_state(AVFormatContext *s)
+{
+ int i;
+ AVStream *st;
+ AVStreamState *ss;
+ AVParserState *state = (AVParserState*) av_malloc(sizeof(AVParserState));
+ if (!state)
+ return NULL;
+
+ state->stream_states = (AVStreamState*) av_malloc(sizeof(AVStreamState) * s->nb_streams);
+ if (!state->stream_states) {
+ av_free(state);
+ return NULL;
+ }
+
+ state->fpos = url_ftell(s->pb);
+
+ // copy context structures
+ state->cur_st = s->cur_st;
+ state->packet_buffer = s->packet_buffer;
+ state->raw_packet_buffer = s->raw_packet_buffer;
+ state->raw_packet_buffer_remaining_size = s->raw_packet_buffer_remaining_size;
+
+ s->cur_st = NULL;
+ s->packet_buffer = NULL;
+ s->raw_packet_buffer = NULL;
+ s->raw_packet_buffer_remaining_size = RAW_PACKET_BUFFER_SIZE;
+
+ // copy stream structures
+ state->nb_streams = s->nb_streams;
+ for (i = 0; i < s->nb_streams; i++) {
+ st = s->streams[i];
+ ss = &state->stream_states[i];
+
+ ss->parser = st->parser;
+ ss->last_IP_pts = st->last_IP_pts;
+ ss->cur_dts = st->cur_dts;
+ ss->reference_dts = st->reference_dts;
+ ss->cur_ptr = st->cur_ptr;
+ ss->cur_len = st->cur_len;
+ ss->probe_packets = st->probe_packets;
+ ss->cur_pkt = st->cur_pkt;
+
+ st->parser = NULL;
+ st->last_IP_pts = AV_NOPTS_VALUE;
+ st->cur_dts = AV_NOPTS_VALUE;
+ st->reference_dts = AV_NOPTS_VALUE;
+ st->cur_ptr = NULL;
+ st->cur_len = 0;
+ st->probe_packets = MAX_PROBE_PACKETS;
+ av_init_packet(&st->cur_pkt);
+ }
+
+ return state;
+}
+
+void ff_restore_parser_state(AVFormatContext *s, AVParserState *state)
+{
+ int i;
+ AVStream *st;
+ AVStreamState *ss;
+ av_read_frame_flush(s);
+
+ if (!state)
+ return;
+
+ url_fseek(s->pb, state->fpos, SEEK_SET);
+
+ // copy context structures
+ s->cur_st = state->cur_st;
+ s->packet_buffer = state->packet_buffer;
+ s->raw_packet_buffer = state->raw_packet_buffer;
+ s->raw_packet_buffer_remaining_size = state->raw_packet_buffer_remaining_size;
+
+ // copy stream structures
+ for (i = 0; i < state->nb_streams; i++) {
+ st = s->streams[i];
+ ss = &state->stream_states[i];
+
+ st->parser = ss->parser;
+ st->last_IP_pts = ss->last_IP_pts;
+ st->cur_dts = ss->cur_dts;
+ st->reference_dts = ss->reference_dts;
+ st->cur_ptr = ss->cur_ptr;
+ st->cur_len = ss->cur_len;
+ st->probe_packets = ss->probe_packets;
+ st->cur_pkt = ss->cur_pkt;
+ }
+
+ av_free(state->stream_states);
+ av_free(state);
+}
+
+static void free_packet_list(AVPacketList *pktl)
+{
+ AVPacketList *cur;
+ while (pktl) {
+ cur = pktl;
+ pktl = cur->next;
+ av_free_packet(&cur->pkt);
+ av_free(cur);
+ }
+}
+
+void ff_free_parser_state(AVFormatContext *s, AVParserState *state)
+{
+ int i;
+ AVStreamState *ss;
+
+ if (!state)
+ return;
+
+ for (i = 0; i < state->nb_streams; i++) {
+ ss = &state->stream_states[i];
+ if (ss->parser)
+ av_parser_close(ss->parser);
+ av_free_packet(&ss->cur_pkt);
+ }
+
+ free_packet_list(state->packet_buffer);
+ free_packet_list(state->raw_packet_buffer);
+
+ av_free(state->stream_states);
+ av_free(state);
+}
+
Added: trunk/libavformat/seek.h
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ trunk/libavformat/seek.h Sat Aug 22 18:05:43 2009 (r19680)
@@ -0,0 +1,97 @@
+/*
+ * Utility functions for seeking for use within FFmpeg format handlers.
+ *
+ * Copyright (c) 2009 Ivan Schreter
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVFORMAT_SEEK_H
+#define AVFORMAT_SEEK_H
+
+#include "avformat.h"
+
+/// Opaque structure for parser state.
+typedef struct AVParserState AVParserState;
+
+/**
+ * Search for sync point of all active streams.
+ *
+ * This is not supposed to be called directly by a user application,
+ * but by demuxers.
+ *
+ * A sync point is a point in stream, so that decoding from this point,
+ * output of decoders of all streams synchronizes closest to given timestamp
+ * ts (but taking timestamp limits into account, i.e., no sooner than ts_min
+ * and no later than ts_max).
+ *
+ * @param stream_index stream index for time base reference of timestamps.
+ * @param pos approximate position where to start searching for key frames.
+ * @param min_ts minimum allowed timestamp (position, if AVSEEK_FLAG_BYTE set).
+ * @param ts target timestamp (or position, if AVSEEK_FLAG_BYTE set in flags).
+ * @param max_ts maximum allowed timestamp (position, if AVSEEK_FLAG_BYTE set).
+ * @param flags if AVSEEK_FLAG_ANY is set, seek to any frame, otherwise only
+ * to a keyframe. If AVSEEK_FLAG_BYTE is set, search by
+ * position, not by timestamp.
+ * @return < 0 if no such sync point could be found, otherwise stream position
+ * (stream is repositioned to this position).
+ */
+int64_t ff_gen_syncpoint_search(AVFormatContext *s,
+ int stream_index,
+ int64_t pos,
+ int64_t min_ts,
+ int64_t ts,
+ int64_t max_ts,
+ int flags);
+
+/**
+ * Store current parser state and file position.
+ *
+ * This function can be used by demuxers before destructive seeking algorithm
+ * to store parser state. After the seek, depending on outcome, original state
+ * can be restored or new state kept and original state freed.
+ *
+ * @note As a side effect, original parser state is reset, since structures
+ * are relinked to stored state instead of being deeply-copied (for
+ * performance reasons and to keep code simple).
+ *
+ * @param s context from which to save state.
+ * @return parser state object or NULL if memory could not be allocated.
+ */
+AVParserState *ff_store_parser_state(AVFormatContext *s);
+
+/**
+ * Restore previously saved parser state and file position.
+ *
+ * Saved state will be invalidated and freed by this call, since internal
+ * structures will be relinked back to stored state instead of being
+ * deeply-copied.
+ *
+ * @param s context to which to restore state (same as used for storing state).
+ * @param state state to restore.
+ */
+void ff_restore_parser_state(AVFormatContext *s, AVParserState *state);
+
+/**
+ * Free previously saved parser state.
+ *
+ * @param s context to which the state belongs (same as used for storing state).
+ * @param state state to free.
+ */
+void ff_free_parser_state(AVFormatContext *s, AVParserState *state);
+
+#endif /* AVFORMAT_SEEK_H */
Modified: trunk/libavformat/utils.c
==============================================================================
--- trunk/libavformat/utils.c Sat Aug 22 17:56:06 2009 (r19679)
+++ trunk/libavformat/utils.c Sat Aug 22 18:05:43 2009 (r19680)
@@ -1140,7 +1140,7 @@ int av_find_default_stream_index(AVForma
/**
* Flush the frame reader.
*/
-static void av_read_frame_flush(AVFormatContext *s)
+void av_read_frame_flush(AVFormatContext *s)
{
AVStream *st;
int i;
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