lavf/matroskaenc: Assume 48kHz sample rate for Opus initial padding.

Analyzed by Timothy B. Terriberry in Mozilla bug 1227153.
Fixes ticket #5121.

libavformat/matroskaenc.c

@@ -924,7 +924,7 @@ static int mkv_write_track(AVFormatContext *s, MatroskaMuxContext *mkv,
 
     if (codec->codec_type == AVMEDIA_TYPE_AUDIO && codec->initial_padding && codec->codec_id == AV_CODEC_ID_OPUS) {
         int64_t codecdelay = av_rescale_q(codec->initial_padding,
-                                          (AVRational){ 1, codec->sample_rate },
+                                          (AVRational){ 1, 48000 },
                                           (AVRational){ 1, 1000000000 });
         if (codecdelay < 0) {
             av_log(s, AV_LOG_ERROR, "Initial padding is invalid\n");

libavformat/version.h

@@ -31,7 +31,7 @@
 
 #define LIBAVFORMAT_VERSION_MAJOR  57
 #define LIBAVFORMAT_VERSION_MINOR  21
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \