avcodec/mpegvideo: make mc_mb_var_sum_temp / mb_var_sum_temp 64bit

This avoids a hypothetical integer overflow with very high resolution video

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/mpegvideo: make mc_mb_var_sum / mb_var_sum 64bit

This avoids a hypothetical integer overflow with very high resolution video

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/ratecontrol: make (mc_)mb_var_sum(_last) 64bit

This avoids hypothetical integer overflows
avcodec/snowenc: allow larger mb variances

Fixes assertion failure
Fixes Ticket3463

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>