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FFmpeg/libavformat/options.c
Andreas Rheinhardt c602deb138 avformat/mux: Preserve sync even if later packet has negative ts
write_packet() has code to shift the packets timestamps
to make them nonnegative or even make them start at ts zero;
this code inspects every packet that is written and if a packet
with negative timestamp (whether this is dts or pts depends upon
another flag; basically: Matroska uses pts, everyone else dts)
is encountered, this is offset to make the timestamp zero.
All further packets will be offset accordingly (with the offset
converted according to the streams' timebases).

This is based around an assumption, namely that the timestamps
are indeed non-decreasing, so that the first packet with negative
timestamps is the first packet with timestamps. This assumption
is often fulfilled given that the default interleavement function
by default interleaves per dts; yet there are scenarios in which
it may not be fulfilled:
a) av_write_frame() instead of av_interleaved_write_frame() is used.
b) The audio_preload option is used.
c) When the timestamps that are made nonnegative/zero are pts
(i.e. with Matroska), because the packet with the smallest dts
is not necessarily the packet with the smallest pts.
d) Possibly with custom interleavement functions.
In these cases the relative sync of the first few packet(s) is offset
relative to the later packets. This contradicts the documentation
("When shifting is enabled, all output timestamps are shifted by
the same amount").

Therefore this commit changes this: As soon as the first packet
with valid timestamps is output, it is checked and recorded whether
the timestamps need to be shifted. Further packets are no longer
checked for needing to be offset; instead they are simply offset.
In the cases above this leads to packets with negative timestamps
(and the appropriate warnings) instead of desync. This will mostly
be fixed in the next commit.

This commit also factors handling the avoid_negative_ts stuff out
of write_packet() in order to be able to return immediately.

Tickets #4536 and #5784 as well as the matroska-avoid-negative-ts-test
are examples of c); as has been said, some timestamps are now negative,
yet the ref file update does not show it because ffmpeg.c sanitizes
the timestamps (-copyts disables it; ffprobe and mkvinfo also show
the original timestamps).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
2022-01-21 16:47:38 +01:00

191 lines
5.1 KiB
C

/*
* Copyright (c) 2000, 2001, 2002 Fabrice Bellard
*
* 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 "avformat.h"
#include "avio_internal.h"
#include "internal.h"
#include "libavutil/avassert.h"
#include "libavutil/internal.h"
#include "libavutil/opt.h"
/**
* @file
* Options definition for AVFormatContext.
*/
FF_DISABLE_DEPRECATION_WARNINGS
#include "options_table.h"
FF_ENABLE_DEPRECATION_WARNINGS
static const char* format_to_name(void* ptr)
{
AVFormatContext* fc = (AVFormatContext*) ptr;
if(fc->iformat) return fc->iformat->name;
else if(fc->oformat) return fc->oformat->name;
else return "NULL";
}
static void *format_child_next(void *obj, void *prev)
{
AVFormatContext *s = obj;
if (!prev && s->priv_data &&
((s->iformat && s->iformat->priv_class) ||
s->oformat && s->oformat->priv_class))
return s->priv_data;
if (s->pb && s->pb->av_class && prev != s->pb)
return s->pb;
return NULL;
}
enum {
CHILD_CLASS_ITER_AVIO = 0,
CHILD_CLASS_ITER_MUX,
CHILD_CLASS_ITER_DEMUX,
CHILD_CLASS_ITER_DONE,
};
#define ITER_STATE_SHIFT 16
static const AVClass *format_child_class_iterate(void **iter)
{
// we use the low 16 bits of iter as the value to be passed to
// av_(de)muxer_iterate()
void *val = (void*)(((uintptr_t)*iter) & ((1 << ITER_STATE_SHIFT) - 1));
unsigned int state = ((uintptr_t)*iter) >> ITER_STATE_SHIFT;
const AVClass *ret = NULL;
if (state == CHILD_CLASS_ITER_AVIO) {
ret = &ff_avio_class;
state++;
goto finish;
}
if (state == CHILD_CLASS_ITER_MUX) {
const AVOutputFormat *ofmt;
while ((ofmt = av_muxer_iterate(&val))) {
ret = ofmt->priv_class;
if (ret)
goto finish;
}
val = NULL;
state++;
}
if (state == CHILD_CLASS_ITER_DEMUX) {
const AVInputFormat *ifmt;
while ((ifmt = av_demuxer_iterate(&val))) {
ret = ifmt->priv_class;
if (ret)
goto finish;
}
val = NULL;
state++;
}
finish:
// make sure none av_(de)muxer_iterate does not set the high bits of val
av_assert0(!((uintptr_t)val >> ITER_STATE_SHIFT));
*iter = (void*)((uintptr_t)val | (state << ITER_STATE_SHIFT));
return ret;
}
static AVClassCategory get_category(void *ptr)
{
AVFormatContext* s = ptr;
if(s->iformat) return AV_CLASS_CATEGORY_DEMUXER;
else return AV_CLASS_CATEGORY_MUXER;
}
static const AVClass av_format_context_class = {
.class_name = "AVFormatContext",
.item_name = format_to_name,
.option = avformat_options,
.version = LIBAVUTIL_VERSION_INT,
.child_next = format_child_next,
.child_class_iterate = format_child_class_iterate,
.category = AV_CLASS_CATEGORY_MUXER,
.get_category = get_category,
};
static int io_open_default(AVFormatContext *s, AVIOContext **pb,
const char *url, int flags, AVDictionary **options)
{
int loglevel;
if (!strcmp(url, s->url) ||
s->iformat && !strcmp(s->iformat->name, "image2") ||
s->oformat && !strcmp(s->oformat->name, "image2")
) {
loglevel = AV_LOG_DEBUG;
} else
loglevel = AV_LOG_INFO;
av_log(s, loglevel, "Opening \'%s\' for %s\n", url, flags & AVIO_FLAG_WRITE ? "writing" : "reading");
return ffio_open_whitelist(pb, url, flags, &s->interrupt_callback, options, s->protocol_whitelist, s->protocol_blacklist);
}
static int io_close2_default(AVFormatContext *s, AVIOContext *pb)
{
return avio_close(pb);
}
AVFormatContext *avformat_alloc_context(void)
{
FFFormatContext *const si = av_mallocz(sizeof(*si));
AVFormatContext *s;
if (!si)
return NULL;
s = &si->pub;
s->av_class = &av_format_context_class;
s->io_open = io_open_default;
s->io_close = ff_format_io_close_default;
s->io_close2= io_close2_default;
av_opt_set_defaults(s);
si->pkt = av_packet_alloc();
si->parse_pkt = av_packet_alloc();
if (!si->pkt || !si->parse_pkt) {
avformat_free_context(s);
return NULL;
}
si->shortest_end = AV_NOPTS_VALUE;
return s;
}
enum AVDurationEstimationMethod av_fmt_ctx_get_duration_estimation_method(const AVFormatContext* ctx)
{
return ctx->duration_estimation_method;
}
const AVClass *avformat_get_class(void)
{
return &av_format_context_class;
}