Increased fifo decoder size to 400mb.

 I don't think there is any good fixed value, I have tuned it for
50mbit/s video with a cache of 60s.

src/input/decoder.c

@@ -373,7 +373,7 @@ void input_DecoderDecode( decoder_t *p_dec, block_t *p_block, bool b_do_pace )
         if( !p_owner->b_buffering )
             block_FifoPace( p_owner->p_fifo, 10, SIZE_MAX );
     }
-    else if( block_FifoSize( p_owner->p_fifo ) > 50000000 /* 50 MB */ )
+    else if( block_FifoSize( p_owner->p_fifo ) > 400000000 /* 400 MB, ie ~ 50mb/s for 60s */ )
     {
         /* FIXME: ideally we would check the time amount of data
          * in the FIFO instead of its size. */