H.261 Datasheet, PDF (29/31 Pages) List of Unclassifed Manufacturers – LINE TRANSMISSION OF NON-TELEPHONE SIGNALS

H RD b uffe r
occu pan cy
(b it )
t_{n+ 1}
R (t )dt
t_n
B
d _n+1
b_n
t_n
b _n+1
t _n+1
T ime
( C IF in te rva l)
T 1 502 470- 90/d09
NOTE - Time (tn+1 - tn) is an integer number of CIF picture periods (1/29.97, 2/29.97, 3/29.97, ...).
FIGURE B.1/H.261...[D09] = 9CM
FIGURE B.1/H.261
HRD buffer occupancy
Annex C
Codec delay measurement method
(This annex forms an integral part of this Recommendation)
The video encoder and video decoder delays will vary depending on implementation. The delay will also depend on the
picture format (QCIF, CIF) and data rate in use. This annex specifies the method by which the delay figures are established
for a particular design. To allow correct audio delay compensation the overall video delay needs to be established from a user
perception point of view under typical viewing conditions.
Point A is the video input to the video coder. Point B is the channel output from the video terminal (i.e. including any FEC,
channel framing, etc.). Point C is the video output from the decoder.
A video sequence lasting more than 100 seconds is connected to the video coder input (point A) in Figure C.1 above. The
video sequence should have the following characteristics:
– it should contain a typical moving scene consistent with the intended purpose of the video codec;
– it should produce a minimum coded picture rate of 7.5 Hz at the bit rate in use;
– it should contain a visible identification mark at intervals throughout the length of the sequence. The visible
identification should change every 97 video input frames and be located within the picture area represented by
the first GOB in the picture. For example, the first block in the picture could change from black to white at
intervals of 97 video frame periods. The identification mark should be chosen so that it can be detected at
point B and does not significantly contribute to the overall coding performance.
The codec and video sequence should be arranged so that the bitstream contains less than 10% stuffing (MBA stuffing +
error correction fill bits).
The encoder delay is obtained by measuring the time from when the visible identification changes at point A to the time that
the change is detected at point B. Similarly, the decoder delay is obtained by taking measurements at points B and C.
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Recommendation H.261 (03/93)