[FFmpeg-devel] [PATCH] First shot at AVCHD seeking via new seeking API
Michael Niedermayer
michaelni
Thu Aug 27 03:00:43 CEST 2009
On Sun, Aug 09, 2009 at 04:50:33PM +0200, Ivan Schreter wrote:
> Hi Baptiste,
>
> Ivan Schreter wrote:
>> [...]
>> Ok, so I'll implement your proposal regarding active flag and the
>> optimization for ts == max_ts. Per-stream term position is in my opinion
>> still necessary. Will it be OK to commit then?
> Attached is the newest version of the patch.
>
> I've addressed these points:
>
> * Removed "active" flag and replaced it with st->discard checking.
> * Also removed "found_hi" and "found_lo" flags, as the position can
> be used for that.
> * Added optimization for ts < ts_max by initializing terminating
> condition to ts_max for first iteration. Also, instead of
> positions, timestamps are used per-stream as terminating condition
> (makes the code for TS and byte seeking exactly the same).
> * Removed "fpos" approximation of frame position and instead keeping
> last-known position for multi-frame packets.
> * Per your request, I added saving/restoring of parser state to
> seek.c and calls to it in mpegts.c, so seeking to invalid position
> won't invalidate current stream state (or in other words, it will
> restore the state just before seeking, so next frame will be read
> as if no seek was attempted). This can be used generically, so I
> exposed it in seek.h.
>
> I hope it's now OK to commit.
>
> I also have code handling MPEG-PS ready (using the same method and same
> routines in seek.c and basically the same implementation of read_seek2 as
> in mpegts.c), but there is the issue of partial frame read, which needs to
> be addressed first (another thread on ML).
>
> Regards,
>
> Ivan
>
> Makefile | 2
> seek.c | 500 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> seek.h | 97 ++++++++++++
> utils.c | 2
> 4 files changed, 599 insertions(+), 2 deletions(-)
> 306fe878e49fc2dab68d43d62a7f105c87359bcd seek_cooked_lavf.patch
> Index: libavformat/utils.c
> ===================================================================
> --- libavformat/utils.c (revision 19507)
> +++ libavformat/utils.c (working copy)
> @@ -1140,7 +1140,7 @@
> /**
> * Flush the frame reader.
> */
> -static void av_read_frame_flush(AVFormatContext *s)
> +void av_read_frame_flush(AVFormatContext *s)
> {
> AVStream *st;
> int i;
seperate patch
> Index: libavformat/Makefile
> ===================================================================
> --- libavformat/Makefile (revision 19507)
> +++ libavformat/Makefile (working copy)
> @@ -5,7 +5,7 @@
>
> 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 utils.o seek.o
>
> # muxers/demuxers
> OBJS-$(CONFIG_AAC_DEMUXER) += raw.o id3v1.o id3v2.o
> Index: libavformat/seek.c
> ===================================================================
> --- libavformat/seek.c (revision 0)
> +++ libavformat/seek.c (revision 0)
> @@ -0,0 +1,500 @@
seek.c should be created by forking utils.c via svn cp and later new code
should be added (svn needs that to keep track of line history)
> +/*
> + * 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;
storing and restoring parser state also belongs in a seperate patch and
it requires discussion in a seperate thread and the code belongs, well
into some parser related file more than a seek related one.
but above all, your code really is ugly, and would add a quite
substantial burden in terms of maintaince. More precissely every
field added would have to be added to these structs and copy and
restore routines would have to be updated.
This design IS poor. And i doubt it works at all
also, the first obvious way to restore state is a simple seek back
and demux + parse until the last packet while discardng packets
[...]
> +/**
> + * 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 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,
> + 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 common AV_TIME_BASE or position 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->pts_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
isnt that a bug?
> + // 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;
> + } else {
> + // Rescale stream timestamp to AV_TIME_BASE.
> + ts = av_rescale(pts, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);
why? all comparissions are inaccurate after this, didnt you say you
fixed that?
> + }
> +
> + 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;
> + }
> +
> + if (sp->term_ts != AV_NOPTS_VALUE && ts > sp->term_ts) {
> + // 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->pts_hi = INT64_MAX;
> + sp->pos_hi = INT64_MAX - 1;
> + }
> + if (terminated_count == keyframes_to_find)
> + break; // all terminated, iteration done
> + }
> + continue;
> + }
> +
> + if (ts <= timestamp) {
> + // Keyframe found before target timestamp.
> + if (sp->pos_lo == INT64_MAX) {
> + // Found first keyframe lower than target timestamp.
> + (*found_lo)++;
> + sp->pts_lo = ts;
> + sp->pos_lo = pos;
> + } else if (sp->pts_lo < ts) {
> + // Found a better match (closer to target timestamp).
> + sp->pts_lo = ts;
> + sp->pos_lo = pos;
> + }
duplicate
> + }
> + if (ts >= timestamp) {
> + // Keyframe found after target timestamp.
> + if (sp->pos_hi == INT64_MAX) {
> + // Found first keyframe higher than target timestamp.
> + (*found_hi)++;
> + sp->pts_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->pts_hi > ts) {
> + // Found a better match (actually, shouldn't happen).
> + sp->pts_hi = ts;
> + sp->pos_hi = pos;
> + }
same issue
> + }
> + }
> + }
> +
> + // 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;
> + int64_t min_pos = 0;
> + int first_iter = 1;
> +
> + if (stream_index >= 0 && !(flags & AVSEEK_FLAG_BYTE)) {
> + // Rescale timestamps to AV_TIME_BASE, if timestamp of a reference stream given.
> + st = s->streams[stream_index];
> + if (ts != AV_NOPTS_VALUE)
> + ts = av_rescale(ts, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);
> + if (ts_min != INT64_MIN)
> + ts_min = av_rescale(ts_min, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);
> + if (ts_max != INT64_MAX)
> + ts_max = av_rescale(ts_max, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);
> + }
more rescaling that probably shouldnt be ...
> +
> + // Initialize syncpoint structures for each stream.
> + sync = (AVSyncPoint*) av_malloc(s->nb_streams * sizeof(AVSyncPoint));
I think you did not implement a syncpoint cache and you completely ignore
the existing AVIndexes
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
The educated differ from the uneducated as much as the living from the
dead. -- Aristotle
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