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avformat/utils: Change compute_chapters_end() from O(n²) to O(n log n)

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Fixes: Timeout (49sec -> 9sec)
Fixes: 27427/clusterfuzz-testcase-minimized-ffmpeg_dem_FFMETADATA_fuzzer-5140589838073856

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2020-11-21 14:51:25 +01:00
parent a454a0c14f
commit ac5a568e6d
1 changed files with 34 additions and 12 deletions
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46
libavformat/utils.c
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@ -3193,31 +3193,51 @@ enum AVCodecID av_codec_get_id(const AVCodecTag *const *tags, unsigned int tag)
return AV_CODEC_ID_NONE;
}
static void compute_chapters_end(AVFormatContext *s)
static int chapter_start_cmp(const void *p1, const void *p2)
{
unsigned int i, j;
AVChapter *ch1 = *(AVChapter**)p1;
AVChapter *ch2 = *(AVChapter**)p2;
int delta = av_compare_ts(ch1->start, ch1->time_base, ch2->start, ch2->time_base);
if (delta)
return delta;
return (ch1 > ch2) - (ch1 < ch2);
}
static int compute_chapters_end(AVFormatContext *s)
{
unsigned int i;
int64_t max_time = 0;
AVChapter **timetable = av_malloc(s->nb_chapters * sizeof(*timetable));
if (!timetable)
return AVERROR(ENOMEM);
if (s->duration > 0 && s->start_time < INT64_MAX - s->duration)
max_time = s->duration +
((s->start_time == AV_NOPTS_VALUE) ? 0 : s->start_time);
for (i = 0; i < s->nb_chapters; i++)
if (s->chapters[i]->end == AV_NOPTS_VALUE) {
AVChapter *ch = s->chapters[i];
int64_t end = max_time ? av_rescale_q(max_time, AV_TIME_BASE_Q,
ch->time_base)
: INT64_MAX;
timetable[i] = s->chapters[i];
qsort(timetable, s->nb_chapters, sizeof(*timetable), chapter_start_cmp);
for (j = 0; j < s->nb_chapters; j++) {
AVChapter *ch1 = s->chapters[j];
for (i = 0; i < s->nb_chapters; i++)
if (timetable[i]->end == AV_NOPTS_VALUE) {
AVChapter *ch = timetable[i];
int64_t end = max_time ? av_rescale_q(max_time, AV_TIME_BASE_Q,
ch->time_base)
: INT64_MAX;
if (i + 1 < s->nb_chapters) {
AVChapter *ch1 = timetable[i + 1];
int64_t next_start = av_rescale_q(ch1->start, ch1->time_base,
ch->time_base);
if (j != i && next_start > ch->start && next_start < end)
ch->time_base);
if (next_start > ch->start && next_start < end)
end = next_start;
}
ch->end = (end == INT64_MAX || end < ch->start) ? ch->start : end;
}
av_free(timetable);
return 0;
}
static int get_std_framerate(int i)
@ -4073,7 +4093,9 @@ FF_ENABLE_DEPRECATION_WARNINGS
}
}
compute_chapters_end(ic);
ret = compute_chapters_end(ic);
if (ret < 0)
goto find_stream_info_err;
/* update the stream parameters from the internal codec contexts */
for (i = 0; i < ic->nb_streams; i++) {