H.261
| Model | H.261 |
| Description | LINE TRANSMISSION OF NON-TELEPHONE SIGNALS |
| PDF file | Total 31 pages (File size: 126K) |
| Chip Manufacturer | ETC |
long i,j;
double x;
/* double is 64 bits */
randx
=
(randx * 1103515245)
+
12345;
i
=
randx & 0x7ffffffe;
/* keep 30 bits */
x
=
( (double)i ) / z;
/* range 0 to 0.99999 ... */
x *
=
(L+H+1);
/* range 0 to
<
L+H+1 */
j
=
x;
/* truncate to integer */
return( j – L);
/* range
−L
to H */
}
Annex B
Hypothetical reference decoder
(This annex forms an integral part of this Recommendation)
The hypothetical reference decoder (HRD) is defined as follows:
B.1
The HRD and the encoder have the same clock frequency as well as the same CIF rate, and are operated
synchronously.
B.2
The HRD receiving buffer size is (B
+
256 kbits). The value of
B
is defined as follows:
B
=
4R
max
/29.97 where
R
max
is the maximum video bit rate to be used in the connection.
B.3
The HRD buffer is initially empty.
B.4
The HRD buffer is examined at CIF intervals (
≈
33 ms). If at least one complete coded picture is in the buffer then
all the data for the earliest picture is instantaneously removed (e.g. at
t
n+1
in Figure B.1). Immediately after removing the
above data the buffer occupancy must be less than
B.
This is a requirement on the coder output bitstream including coded
picture data and MBA stuffing but not error correction framing bits, fill indicator (Fi), fill bits or error correction parity
information described in 5.4.
To meet this requirement the number of bits for the (n+1)th coded picture
d
n+1
must satisfy:
t
n
+
1
d
n
+
1
≥
b
n
+
t
n
z
R(t )dt
−
B
where
b
n
is buffer occupancy just after the time
t
n
;
t
n
is the time the
nth
coded picture is removed from the HRD buffer;
R(t)
is the video bit rate at the time
t.
Recommendation H.261
(03/93)
25
