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[188.192.142.35]) by smtp.gmail.com with ESMTPSA id n9sm3372511wrt.93.2019.11.26.21.39.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 Nov 2019 21:39:12 -0800 (PST) From: Andreas Rheinhardt To: ffmpeg-devel@ffmpeg.org Date: Wed, 27 Nov 2019 06:38:40 +0100 Message-Id: <20191127053842.19481-3-andreas.rheinhardt@gmail.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191127053842.19481-1-andreas.rheinhardt@gmail.com> References: <20191106024922.19228-3-andreas.rheinhardt@gmail.com> <20191127053842.19481-1-andreas.rheinhardt@gmail.com> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH v2 3/5] avformat/matroskaenc: Reuse random seed X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Cc: Andreas Rheinhardt Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" 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 --- libavformat/matroskaenc.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c index 98be7f7a2f..aecd776157 100644 --- a/libavformat/matroskaenc.c +++ b/libavformat/matroskaenc.c @@ -160,6 +160,8 @@ 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, @@ -1909,15 +1911,7 @@ 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"; @@ -2738,9 +2732,14 @@ 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];