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<concept id="GUID-9DC82237-3A81-53C8-97A7-8ACA5C97A5EC" xml:lang="en"><title>Overview</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<section><title>Purpose</title> <p>The AMR payload formatter provides APIs

to pack and unpack AMR encoded data as per <xref href="http://www.faqs.org/rfcs/rfc3267.html" scope="external">RFC 3267</xref>, 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. </p> </section>

<section><title>Required background</title> <p>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. </p> </section>

<section><title>Key concepts</title> <dl>

<dlentry>

<dt>Adaptive Multi-Rate (AMR)</dt>

<dd><p>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. </p> </dd>

</dlentry>

</dl> <dl>

<dlentry>

<dt>Codec</dt>

<dd><p>A codec is a device or a program capable of encoding and decoding a

digital data stream or signal. </p> </dd>

</dlentry>

</dl> </section>

<section><title>API summary </title> <table id="GUID-14F0C0C3-7D1C-5054-95EA-3BB783A1D117">

<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

<thead>

<row>

<entry>Class Name</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

<entry><p> <xref href="GUID-2283C5F3-9237-38BE-933C-353ADF676B42.dita#GUID-2283C5F3-9237-38BE-933C-353ADF676B42/GUID-F885E957-C375-3CF9-82B7-2611B0974675"><apiname>CStreamFormatter::Pack()</apiname></xref>  </p> </entry>

<entry><p>An API that is used to pack the encoded AMR data. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-2283C5F3-9237-38BE-933C-353ADF676B42.dita#GUID-2283C5F3-9237-38BE-933C-353ADF676B42/GUID-B2F9AE75-87B9-3331-91DA-8FDA72E317F2"><apiname>CStreamFormatter::Unpack()</apiname></xref>  </p> </entry>

<entry><p>An API that is used to extract the AMR payload header from the data

and gives it back to the application. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-2283C5F3-9237-38BE-933C-353ADF676B42.dita#GUID-2283C5F3-9237-38BE-933C-353ADF676B42/GUID-801B3E2A-2B63-35A9-A871-7519D4869326"><apiname>CStreamFormatter::SetStreamProperty()</apiname></xref>  </p> </entry>

<entry><p>An API that is used to set the identified AMR stream properties

if the session has already started. </p> </entry>

</row>

<row>

<entry><p> <xref href="GUID-2283C5F3-9237-38BE-933C-353ADF676B42.dita#GUID-2283C5F3-9237-38BE-933C-353ADF676B42/GUID-447345B5-1F60-3273-A320-B313D388748B"><apiname>CStreamFormatter::GetStreamProperty()</apiname></xref>  </p> </entry>

<entry><p>An API that is used to get the current AMR stream properties for

the session in progress. </p> </entry>

</row>

</tbody>

</tgroup>

</table> </section>

<section><title>Typical uses</title> <p>An application using the AMR plug-in

component must include <filepath>streamformatter.h</filepath>, <filepath>amrproperty.h</filepath>, <filepath>ecom.h</filepath> and<filepath> ECOM.lib</filepath> 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. </p> <p>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 <codeph>CStreamFormatter::NewL()</codeph> function.

This function is overloaded, that is, it takes as default the AMR payload

formatter or any formatter the user has. </p> <p><b>Creating the interface</b> </p> <p>A

user must first create the interface to use the AMR payload formatter. For

more information on creating the interface see, <xref href="GUID-F5D2C8DF-58B5-5620-824B-86BE72341DF7.dita">How

to Create the Interface</xref>. </p> <p><b>Packing and unpacking the AMR encoded

data</b> </p> <p>The application user uses the <xref href="GUID-2283C5F3-9237-38BE-933C-353ADF676B42.dita#GUID-2283C5F3-9237-38BE-933C-353ADF676B42/GUID-F885E957-C375-3CF9-82B7-2611B0974675"><apiname>CStreamFormatter::Pack()</apiname></xref> and <xref href="GUID-2283C5F3-9237-38BE-933C-353ADF676B42.dita#GUID-2283C5F3-9237-38BE-933C-353ADF676B42/GUID-B2F9AE75-87B9-3331-91DA-8FDA72E317F2"><apiname>CStreamFormatter::Unpack()</apiname></xref> APIs

to pack and unpack the AMR encoded data. For more information on packing and

unpacking the AMR encoded data see, <xref href="GUID-42665F58-7E04-5375-A039-7BBDE218DDE4.dita">How

to Pack and Unpack the AMR Encoded Data</xref>. </p> <p><b>Setting and getting

the AMR stream property</b> </p> <p>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. </p> <p>For

more information see, <xref href="GUID-CCFFFE06-1FB8-56C8-874C-C4C1B936FAA4.dita">How

to Set and Get the AMR Stream Property</xref>. </p> </section>