A video data encoding method for encoding an array of video data values, the method comprising the steps of: frequency-transforming the video data values according to a frequency transform, to generate an array of frequency-transformed values by a matrix-multiplication process using a transform matrix having a data precision greater than six bits, the frequency transform being a discrete cosine transform, defining a 32 x 32 transform matrix M 32 for a 32x32 DCT transform; for an NxN transform where N is 4, 8 or 16, subsampling the 32 x 32 transform matrix M 32 to select a subset of N x N values, the subset M N [ x][ y] of values being defined by: M N x y = M 32 x 2 5 − log 2 N y for x, y = 0.. N − 1; wherein said 32 x 32 transform matrix M 32 is defined as follows: characterized in that the coefficient values of said 32 x 32 transform matrix M 32 are selected according to the data precision from values listed in the following tables: 7-bit 8-bit 9-bit 10-bit 11-bit 12-bit 13-bit 14-bit a 128 256 512 1024 2048 4096 8192 16384 b 166 332 665 1329 2658 5317 10633 21266 c 72 144 288 576 1153 2306 4612 9224 d 178 356 713 1426 2852 5703 11407 22813 e 150 301 601 1203 2406 4811 9622 19244 f 100 200 399 798 1596 3192 6385 12769 g 36 71 143 285 570 1141 2282 4563 h 181 361 722 1445 2890 5780 11560 23120 i 172 345 689 1379 2758 5516 11032 22063 j 160 320 639 1278 2556 5113 10225 20450 k 140 281 562 1123 2246 4493 8986 17972 l 114 229 458 915 1830 3660 7321 14642 m 87 174 347 694 1389 2777 5555 11109 n 50 101 201 403 806 1612 3223 6446 o 18 36 72 145 290 579 1158 2316 p 181 361 722 1444 2888 5777 11553 23106 q 179 357 714 1428 2856 5713 11426 22852 r 175 351 701 1403 2806 5611 11222 22445 s 171 341 683 1365 2731 5462 10924 21848 t 164 328 656 1312 2624 5249 10497 20995 u 155 310 619 1238 2476 4952 9905 19810 v 145 291 581 1163 2325 4650 9301 18601 w 134 268 536 1071 2143 4286 8571 17143 x 123 246 491 982 1965 3929 7859 15718 y 108 216 433 866 1732 3463 6927 13853 z 92 184 367 734 1469 2937 5875 11749 A 77 154 308 615 1231 2461 4923 9846 B 62 124 247 494 988 1977 3954 7908 C 44 87 174 348 697 1393 2787 5573 D 26 51 103 205 410 820 1641 3281 E 7 15 30 59 118 236 473 946 15-bit 16-bit 17-bit 18-bit 19-bit a 32768 65536 131072 262144 524288 b 42532 85065 170129 340259 680517 c 18448 36896 73791 147582 295164 d 45627 91253 182507 365014 730028 e 38489 76977 153954 307909 615817 f 25538 51077 102153 204306 408612 g 9126 18252 36504 73009 146018 h 46240 92479 184958 369917 739833 i 44126 88253 176506 353011 706022 j 40901 81802 163603 327207 654413 k 35944 71887 143775 287550 575099 l 29283 58566 117132 234265 468530 m 22219 44437 88874 177749 355498 n 12892 25784 51569 103137 206275 o 4632 9264 18528 37057 74113 p 46212 92424 184849 369697 739394 q 45704 91407 182815 365630 731260 r 44890 89779 179559 359118 718236 s 43695 87391 174781 349562 699125 t 41990 83979 167959 335918 671836 u 39619 79239 158477 316955 633909 v 37202 74404 148808 297616 595233 w 34285 68570 137140 274281 548561 x 31436 62871 125743 251486 502971 y 27706 55412 110825 221650 443299 z 23498 46997 93993 187986 375972 A 19692 39384 78767 157535 315070 B 15816 31631 63263 126525 253051 C 11146 22292 44584 89168 178337 D 6562 13124 26248 52497 104993 E 1891 3782 7564 15129 30258 20-bit 21-bit 22-bit 23-bit 24-bit a 1048576 2097152 4194304 8388608 16777216 b 1361035 2722070 5444140 10888280 21776560 c 590328 1180657 2361314 4722627 9445255 d 1460056 2920112 5840224 11680448 23360895 e 1231635 2463269 4926539 9853077 19706155 f 817225 1634450 3268899 6537799 13075597 g 292035 584070 1168141 2336282 4672564 h 1479667 2959333 5918667 11837334 23674667 i 1412045 2824090 5648179 11296358 22592717 j 1308827 2617653 5235307 10470613 20941227 k 1150199 2300397 4600795 9201590 18403179 l 937060 1874119 3748238 7496477 14992954 m 710995 1421991 2843981 5687962 11375925 n 412549 825098 1650196 3300393 6600785 o 148227 296454 592908 1185815 2371630 p 1478788 2957576 5915152 11830305 23660609 q 1462520 2925040 5850080 11700160 23400319 r 1436472 2872944 5745888 11491775 22983550 s 1398249 2796498 5592996 11185992 22371984 t 1343671 2687342 5374684 10749368 21498736 u 1267818 2535636 5071272 10142545 20285089 v 1190466 2380931 4761862 9523724 19047449 w 1097123 2194246 4388491 8776982 17553965 x 1005942 2011884 4023769 8047537 16095074 y 886598 1773197 3546394 7092787 14185574 z 751944 1503889 3007778 6015555 12031111 A 630139 1260278 2520556 5041112 10082224 B 506101 1012202 2024405 4048809 8097618 C 356674 713348 1426696 2853391 5706783 D 209987 419973 839947 1679894 3359787 E 60515 121030 242061 484122 968243 frequency-transforming the video data values according to a frequency transform, to generate an array of frequency-transformed values by a matrix-multiplication process using a transform matrix having a data precision greater than six bits, the frequency transform being a discrete cosine transform, defining a 32 x 32 transform matrix M 32 for a 32x32 DCT transform; for an NxN transform where N is 4, 8 or 16, subsampling the 32 x 32 transform matrix M 32 to select a subset of N x N values, the subset M N [ x][ y] of values being defined by: M N x y = M 32 x 2 5 − log 2 N y for x, y = 0.. N − 1;