movenc: Fix a typo in a comment

Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/movenc.c

@@ -3367,7 +3367,7 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
     if (trk->start_dts == AV_NOPTS_VALUE) {
         trk->start_dts = pkt->dts;
         if (trk->frag_discont) {
-            /* Pretend the whole stream started at dts=0, with earlier framgents
+            /* Pretend the whole stream started at dts=0, with earlier fragments
              * already written, with a duration summing up to pkt->dts. */
             trk->frag_start   = pkt->dts;
             trk->start_dts    = 0;