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FFmpeg/libavcodec/mpeg4video_parser.c
Andreas Rheinhardt 832ead2ec4 avcodec/mpeg4videodec: Fix data race when initializing VLCs
Both the MPEG-4 parser as well as the decoder initialized
several VLCs. There is a "static int done = 0;" in order to
guard against initializing these multiple times, but this does
not work when several threads try to initialize these VLCs
concurrently, which can happen when initializing several parsers
at the same time (they don't use the global lock that is used
for codecs without the FF_CODEC_CAP_INIT_THREADSAFE cap; actually,
they don't use any lock at all).

Since ff_mpeg4_decode_picture_header() now aborts early when called
from the parser, it no longer needs to have these VLCs initialized
at all. This commit therefore does exactly this.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
2022-01-09 09:32:53 +01:00

176 lines
5.3 KiB
C

/*
* MPEG-4 video frame extraction
* Copyright (c) 2003 Fabrice Bellard
* Copyright (c) 2003 Michael Niedermayer
*
* 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
*/
#define UNCHECKED_BITSTREAM_READER 1
#include "internal.h"
#include "parser.h"
#include "mpegvideo.h"
#include "mpeg4video.h"
#if FF_API_FLAG_TRUNCATED
/* Nuke this header when removing FF_API_FLAG_TRUNCATED */
#include "mpeg4video_parser.h"
#endif
struct Mp4vParseContext {
ParseContext pc;
Mpeg4DecContext dec_ctx;
int first_picture;
};
#if FF_API_FLAG_TRUNCATED
int ff_mpeg4_find_frame_end(ParseContext *pc, const uint8_t *buf, int buf_size)
#else
/**
* Find the end of the current frame in the bitstream.
* @return the position of the first byte of the next frame, or -1
*/
static int mpeg4_find_frame_end(ParseContext *pc, const uint8_t *buf, int buf_size)
#endif
{
int vop_found, i;
uint32_t state;
vop_found = pc->frame_start_found;
state = pc->state;
i = 0;
if (!vop_found) {
for (i = 0; i < buf_size; i++) {
state = (state << 8) | buf[i];
if (state == VOP_STARTCODE) {
i++;
vop_found = 1;
break;
}
}
}
if (vop_found) {
/* EOF considered as end of frame */
if (buf_size == 0)
return 0;
for (; i < buf_size; i++) {
state = (state << 8) | buf[i];
if ((state & 0xFFFFFF00) == 0x100) {
if (state == SLICE_STARTCODE || state == EXT_STARTCODE)
continue;
pc->frame_start_found = 0;
pc->state = -1;
return i - 3;
}
}
}
pc->frame_start_found = vop_found;
pc->state = state;
return END_NOT_FOUND;
}
/* XXX: make it use less memory */
static int mpeg4_decode_header(AVCodecParserContext *s1, AVCodecContext *avctx,
const uint8_t *buf, int buf_size)
{
struct Mp4vParseContext *pc = s1->priv_data;
Mpeg4DecContext *dec_ctx = &pc->dec_ctx;
MpegEncContext *s = &dec_ctx->m;
GetBitContext gb1, *gb = &gb1;
int ret;
s->avctx = avctx;
s->current_picture_ptr = &s->current_picture;
if (avctx->extradata_size && pc->first_picture) {
init_get_bits(gb, avctx->extradata, avctx->extradata_size * 8);
ret = ff_mpeg4_decode_picture_header(dec_ctx, gb, 1, 1);
if (ret < 0)
av_log(avctx, AV_LOG_WARNING, "Failed to parse extradata\n");
}
init_get_bits(gb, buf, 8 * buf_size);
ret = ff_mpeg4_decode_picture_header(dec_ctx, gb, 0, 1);
if (s->width && (!avctx->width || !avctx->height ||
!avctx->coded_width || !avctx->coded_height)) {
ret = ff_set_dimensions(avctx, s->width, s->height);
if (ret < 0)
return ret;
}
if((s1->flags & PARSER_FLAG_USE_CODEC_TS) && s->avctx->time_base.den>0 && ret>=0){
av_assert1(s1->pts == AV_NOPTS_VALUE);
av_assert1(s1->dts == AV_NOPTS_VALUE);
s1->pts = av_rescale_q(s->time, (AVRational){1, s->avctx->time_base.den}, (AVRational){1, 1200000});
}
s1->pict_type = s->pict_type;
pc->first_picture = 0;
return ret;
}
static av_cold int mpeg4video_parse_init(AVCodecParserContext *s)
{
struct Mp4vParseContext *pc = s->priv_data;
pc->first_picture = 1;
pc->dec_ctx.m.quant_precision = 5;
pc->dec_ctx.m.slice_context_count = 1;
pc->dec_ctx.showed_packed_warning = 1;
return 0;
}
static int mpeg4video_parse(AVCodecParserContext *s,
AVCodecContext *avctx,
const uint8_t **poutbuf, int *poutbuf_size,
const uint8_t *buf, int buf_size)
{
ParseContext *pc = s->priv_data;
int next;
if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
next = buf_size;
} else {
#if FF_API_FLAG_TRUNCATED
next = ff_mpeg4_find_frame_end(pc, buf, buf_size);
#else
next = mpeg4_find_frame_end(pc, buf, buf_size);
#endif
if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
*poutbuf = NULL;
*poutbuf_size = 0;
return buf_size;
}
}
mpeg4_decode_header(s, avctx, buf, buf_size);
*poutbuf = buf;
*poutbuf_size = buf_size;
return next;
}
const AVCodecParser ff_mpeg4video_parser = {
.codec_ids = { AV_CODEC_ID_MPEG4 },
.priv_data_size = sizeof(struct Mp4vParseContext),
.parser_init = mpeg4video_parse_init,
.parser_parse = mpeg4video_parse,
.parser_close = ff_parse_close,
};