Increase maximum encoding video buffer size.

libavutil now supports 64bit RGB formats.

ffmpeg.c

@@ -2621,9 +2621,9 @@ static int transcode_init(OutputFile *output_files, int nb_output_files,
             }
         }
         if (codec->codec_type == AVMEDIA_TYPE_VIDEO) {
-            /* maximum video buffer size is 6-bytes per pixel, plus DPX header size (1664)*/
+            /* maximum video buffer size is 8-bytes per pixel, plus DPX header size (1664)*/
             int size        = codec->width * codec->height;
-            bit_buffer_size = FFMAX(bit_buffer_size, 7*size + 10000);
+            bit_buffer_size = FFMAX(bit_buffer_size, 9*size + 10000);
         }
     }