avcodec: scale pts values to libavcodec scale
avcodec: scale pts values to libavcodec scale

Otherwise bitrate control is quite fobar.

Fixes #11538

Pointed out by Sesse

vlc-mirror/vlc,vlc-mirror/vlc,vlc-mirror/vlc,vlc-mirror/vlc,shyamalschandra/vlc,xkfz007/vlc,xkfz007/vlc,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc