Video: a NAL unit is dropped when the decoder has no free input buffer within 5 ms #89

MediaCodecManager.decodeFrame waits up to 5 ms in dequeueInputBuffer; if no buffer is free, the NAL unit is silently dropped (counted as inputDropped since #84). A dropped slice corrupts the picture until the next key frame. #84/#85 now use these drops as the overload signal, but the drop itself should be avoided where possible: wait longer, or keep a small backlog and drop whole frames (preferably non-reference ones) instead of single NAL units.