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Chap.3 Video and Audio Compression
Table 3.2 shows H.264's bandwidth requirement is lower than MJPEG and MPEG-4 at the same frame rate.
Table 3.2 Bandwidth requirements by MJPEG, MPEG-4 and H.264
Bandwidth
requirement in KByte
3.2 Audio Compression
Major audio compression technologies include G.711, AMR and AAC, which will be introduced below.
3.2.1 G.711
G.711 is a speech compression standard established by ITU in 1972, and is widely used for voice communications
in the telecom industry, where audio quality is not the first priority.
G.711 has a bit rate of 64 kbps. Audio quality of this standard is quite low because signals may suffer from a heavy
loss in digitization.
3.2.2 AMR
AMR (Adaptive Multi-Rate) was announced by 3GPP in 1998, a standard developed for mobile communications.
Its compression ratio is better than G.711 and is widely applied to 3G mobile phones.
AMR bit rate ranges from 4.75 – 12.2 kbps. It offers a higher compression ratio and suffers from a slighter loss
compared with G.711.
3.3.3 AAC
Announced in 1997, AAC (Advanced Audio Coding) is an audio compression standard based on MPEG-2. The
standard is widely used in consumer electronics.
Table 3.3 indicates AAC for music playback purposes offers higher audio quality than G.711 and AMR aimed at
voice communications.
Sample rate (Hz)
Bit rate (bps)
Application
22
CIF 30fps
VGA 30fps
1.3M 5fps
Table 3.3 Comparison of G7.11, AMR and AAC
G.711
8K
64K
General speech
MJPEG
MPEG-4
302
45
819
123
435
155
AMR
8K
4.75K~12.2K
3GPP speech
H.264
27
75
97
AAC
8K ~96K
16K~320K
CD quality
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