Overview

Purpose

The AMR payload formatter provides APIs +to pack and unpack AMR encoded data as per RFC 3267, giving common APIs for future formatter +implementations. This overview shows the usage of APIs included in the AMR +payload formatter component. This component is implemented as an ECOM plug-in +and has a common interface that can be used by other formatter implementations +for codecs like MPEG.

Required background

It is assumed the user has +an understanding of the AMR codec, IF1 and IF2 header formats. The user must +know the valid AMR stream property values and bit rates supported for AMR +wide and narrow band respectively.

Key concepts

Adaptive Multi-Rate (AMR): The AMR codec is a multi-mode codec that supports 8 narrow band speech +encoding modes with bit rates between 4.75 kbps and 12.2 kbps. The sampling +frequency used in AMR is 8000 Hz and the speech encoding is performed +on 20 ms speech frames. So, each encoded AMR speech frame represents 160 samples +of the original speech.

Codec: A codec is a device or a program capable of encoding and decoding a +digital data stream or signal.

API summary + + + +Class Name +Description + + + + +

CStreamFormatter::Pack()

An API that is used to pack the encoded AMR data.

+ + +

CStreamFormatter::Unpack()

An API that is used to extract the AMR payload header from the data +and gives it back to the application.

+ + +

CStreamFormatter::SetStreamProperty()

An API that is used to set the identified AMR stream properties +if the session has already started.

+ + +

CStreamFormatter::GetStreamProperty()

An API that is used to get the current AMR stream properties for +the session in progress.

+ + + +

Typical uses

An application using the AMR plug-in +component must include streamformatter.h, amrproperty.h, ecom.h and ECOM.lib files, and it uses the DLL that is provided to write the application code. +Here we support both AMR narrow band and AMR wide band.

The user has +a choice to either use the AMR payload formatter or provide the UID of the +implementation that the user wants to use in the CStreamFormatter::NewL() function. +This function is overloaded, that is, it takes as default the AMR payload +formatter or any formatter the user has.

Creating the interface

A +user must first create the interface to use the AMR payload formatter. For +more information on creating the interface see, How +to Create the Interface.

Packing and unpacking the AMR encoded +data

The application user uses the CStreamFormatter::Pack() and CStreamFormatter::Unpack() APIs +to pack and unpack the AMR encoded data. For more information on packing and +unpacking the AMR encoded data see, How +to Pack and Unpack the AMR Encoded Data.

Setting and getting +the AMR stream property

A user has an option to set and get the +AMR stream properties if the user wants to change any of the AMR stream properties. +If a user does not want to change any of the AMR stream properties then it +takes the default values assigned to the respective properties.

For +more information see, How +to Set and Get the AMR Stream Property.