26-11-2012, 02:12 PM
Media Encoding
1Media Encoding.ppt (Size: 759.5 KB / Downloads: 29)
Speech Encoding overview
Develop with circuit-switched telephony
Converting an analog audio signal into a digital signal
Two characters of codec: quality and bandwidth
Codec type:
Pulse Code Modulation
Linear Prediction
GSM-FR
AMR
AMR-WB
SMV
Speech Encoding
Pulse Code Modulation (G.711 or PCM codec)
Used in fixed PSTN
All SIP phone support this codec
Using sampling rate of 8000Hz (8000 samples per second, each sample contain 0.125ms)
Encode the amplitude of audio wave (each 0.125ms) at a point with a single value for each sample
Encode that value by 8bits -> 256 different values, bandwidth 64kbit/s
The mapping process above is called Quantization
Come in two flavors: A-law (Europe) and µ-law (USA)
Video Encoding
Image to be encoded into colored dots called pixels
Pixels corresponds the smallest element of the display and be assigned a color
Resolution of a picture typical 640x480 pixels with depth of 8bit/color total 300kbytes
Compression technique to encode video required for lower bandwidth
Encode video technique type:
Common video codecs
H.263
Mandatory Code in the IMS
Required all IMS terminals support a common codecs for communicating directly without transcoders.
3GPP and 3GPP2 terminal usually use transcoder for communicating together
3GPP terminal support: AMR speech codec, H.263 video codec
3GPP2 terminal providing wideband service support: AMR-WB audio codec