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avformat/matroskaenc: Reuse random seed

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This commit reuses the random seed generated in mkv_init() (to determine
the TrackUIDs) for the SegmentUID in order to avoid a potentially
expensive call to av_get_random_seed().

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2020-01-18 09:27:25 +01:00
parent 45314ff21a
commit 4b18999bee
1 changed files with 9 additions and 10 deletions
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19
libavformat/matroskaenc.c
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@ -159,6 +159,8 @@ typedef struct MatroskaMuxContext {
int wrote_chapters;
int allow_raw_vfw;
uint32_t segment_uid[4];
} MatroskaMuxContext;
/** 2 bytes * 7 for EBML IDs, 7 1-byte EBML lengths, 6 1-byte uint,
@ -1819,15 +1821,7 @@ static int mkv_write_header(AVFormatContext *s)
put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, LIBAVFORMAT_IDENT);
if (mkv->mode != MODE_WEBM) {
uint32_t segment_uid[4];
AVLFG lfg;
av_lfg_init(&lfg, av_get_random_seed());
for (i = 0; i < 4; i++)
segment_uid[i] = av_lfg_get(&lfg);
put_ebml_binary(pb, MATROSKA_ID_SEGMENTUID, segment_uid, 16);
put_ebml_binary(pb, MATROSKA_ID_SEGMENTUID, mkv->segment_uid, 16);
}
} else {
const char *ident = "Lavf";
@ -2659,9 +2653,14 @@ static int mkv_init(struct AVFormatContext *s)
return AVERROR(ENOMEM);
}
if (!(s->flags & AVFMT_FLAG_BITEXACT))
if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
av_lfg_init(&c, av_get_random_seed());
// Calculate the SegmentUID now in order not to waste our random seed.
for (i = 0; i < 4; i++)
mkv->segment_uid[i] = av_lfg_get(&c);
}
for (i = 0; i < s->nb_streams; i++) {
mkv_track *track = &mkv->tracks[i];