Fix probe bug losing video packets.

ds_fill_buffer will actually lose any data from previous
ds_fill_buffer calls.
Use demux_fill_buffer instead to get the intended behaviour.

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@36845 b3059339-0415-0410-9bf9-f77b7e298cf2
Remove pointless "if".

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@36846 b3059339-0415-0410-9bf9-f77b7e298cf2
Use sizeof instead of hardcoded number.

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@36847 b3059339-0415-0410-9bf9-f77b7e298cf2
Allow specifying custom path and name for screenshot files.

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@36848 b3059339-0415-0410-9bf9-f77b7e298cf2