avcodec: encoder: use similar timestamps with audio/video
avcodec: encoder: use similar timestamps with audio/video

As the flow is similar now, timestamps should be too

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc