avformat/mp3enc: use av_copy_packet()

Fixes double free
Fixes Ticket3476

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
elbg: change utility_inc to 64bit

Fixes integer overflow
Fixes Ticket3462

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
dshow: use distinct buffers per stream.

Basically sometimes if you start dropping video packets, you also drop audio packets. Now they each have separate buffers to avoid this unexpected behavior.

Signed-off-by: rogerdpack <rogerpack2005@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>