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
MJPEG
MPEG-4
H.264
CIF 30fps
302
45
27
VGA 30fps
819
123
75
1.3M 5fps
435
155
97
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.
Table 3.3 Comparison of G7.11, AMR and AAC G.711
AMR
AAC
Sample rate (Hz)
8K
8K
8K ~96K
Bit rate (bps)
64K
4.75K~12.2K
16K~320K
General speech
3GPP speech
CD quality
Application
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