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Inside Whitepaper

• Introduction
• Real Producer
• Why RealProducer?
• SureStream advantage
• Encoding
• RealMedia Build Engine
• Input Pins
• Media Samples
• Steps for an Encoding Session
• Conclusion
• References

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Audio Encoding Using RealProducer G2 SDK

Introduction

This paper will focus on the processes surrounding the conversion of an audio file into the RealMedia format. It explains the usability of the RealProducer G2 SDK through code snippets to make the understanding of the COM like implementation of the SDK easier.

Real Producer

RealProducer is a technology from RealNetworks that provides for an easy conversion of non-RealMedia format files to RealMedia files. The purpose of the RealProducer SDK is to allow you to create an application that converts audio, video, events, and image map data into the RealMedia file format. The output file can then be streamed over the Internet or Intranet using a RealServer and viewed with a RealPlayer. An application created with the RealProducer SDK can also broadcast a stream that is sent directly to a RealServer.

Why RealProducer?

The advantages are the following

SureStream advantage

SureStream is a technology by which RealMedia files achieve the following

Encoding

The Entire SDK centers on the concept of Encoding. Lets see how it works.

The general encoding process consists of converting an input data source of one format into an output of a different format. An application that supports encoding will consist of three main components: input sources, an encoding session manager and an encoding engine. The role of the RealProducer SDK is to provide the encoding engine that takes various media input and produces output in the RealMedia format.

The working of the encoding session can be put into blocks as below.

The application using the RealProducer SDK is responsible for interpreting an input source into streams of different data types. For example, a QuickTime source file is interpreted as a stream of audio data and video data. The application then passes logical units of the input data stream into the encoding engine so that the stream can be converted into a RealMedia formatted stream and sent to the RealServer or written to a file.

The SDK is a component like library i.e. the SDK is a collection of interfaces, which the applications should use to accomplish RealMedia file format.

In the RealProducer SDK, "The RealMedia Build Engine" and distinct "Input Pins" for each type of input data represent the encoding engine. The input data that passes through the system is packaged as "Media Samples" objects. The application using the RealProducer SDK should use the RealMedia Build Engine and Input Pins to pass the data through the codecs and create the RealMedia output.

RealMedia Build Engine

This is the primary object of any application using the RealProducer SDK. It is used to set up an encoding session that converts audio to the RealMedia format. It is also responsible for coordinating the entire encoding process. The encoding process creates an output file that can be streamed from RealServers or HTTP Servers, as well as streamed real-time to a RealServer for live broadcasting.

The interface that represents the RealMedia Engine is IRMABuildEngine.

Input Pins

The Input Pins are the actual objects that take the raw audio, video, events, or image maps and convert them by encoding and packetization to a format for streaming. The RealMedia Build Engine exposes an Input Pin for each media type that it supports.

Each input pin supports a specific properties object, which the application will use to define the input source format. Each pin also takes a specific format of input data, which must be passed through the RealMedia Build Engine. The application initializes the Input Pin properties with the properties of the source. After the engine is prepared to encode, the application starts encoding by passing in raw data from each input pin.

The interface that represents the Input Pins is IRMAInputPin.

Media Samples

Media Samples are used as a generic way to pass time stamped data units from a media source to an Input Pin for encoding. For example, a Media Sample can be used to pass a chunk of wav data to the RealAudio Input Pin.

The interface that represents the media samples is IRMAMediaSamples.

Steps for an Encoding Session

Step 1: Set the target audience

Target Audience is the link type on which the resulting file will be streamed. For example, if the file generated will be used only in the local machine, we can set maximum speed

The various target audiences present are

Step2: Create the Engine

Res = RMACreateRMBuildEngine (&g_pRMBuildEngine);

Once the Engine is created enumerate and get all the input pins available and their output mime types.

Now set the other properties for the engine.

g_pRMBuildEngine->SetDoOutputMimeType(MIME_REALAUDIO, g_bAudio); g_pRMBuildEngine->SetDoMultiRateEncoding(TRUE); Res = g_pRMBuildEngine->GetClipProperties (&g_pClipProps); g_pClipProps->SetDoOutputFile (TRUE);

This call ensures that the resulting realmedia file will become a file in the local and not on a real server.

Step 3: Encoding

Since the initialization is complete for the engine, the engine can be started to perform the actual encoding.

There are a total of 21 codecs n the G2 SDK to choose from for encoding.

The appropriate codec is set to the engine. Now the engine is set for the final launch. The encode() function called with chunks of data taken from the input file. This process will continue until the entire input file is converted to a realmedia file.

The encoding steps would be like this

Get the pin using which the Engine will start the encoding. This is a two step process. Firstly the available pins in the Engine should be obtained through the pin enumerator.

IUnknown* tempUnk = NULL; IRMAEnumeratorIUnknown* pPinEnum = NULL; Res = g_pRMBuildEngine->GetPinEnumerator (&pPinEnum);

Once the enumerator is obtained, the Audio pin is obtained by passing through the list of pins provided by the engine.

While (there are pins in the engine) { IRMAInputPin* tempPin = NULL; Res = tempUnk->QueryInterface (IID_IRMAInputPin, (void**)&tempPin); If (currentpin is the required pin) { gAudioPin = tempPin; } ResEnum = pPinEnum->Next (&tempUnk); }

Having got the required pin, get the data to be sent to the input pin.GetFirstAudioSample (pAudSample, suggestedAudioInputSize);

While (samples left in inputfile) { Res = gAudioPin->Encode (pAudSample); Res = GetNextAudioSample (pAudSample); }

Conclusion

The RealProducer G2 SDK is thus a library that provides a COM like implementation of an engine that can be used to convert an audio file to realmedia format.

References

Copyright © 2010 Calsoft Labs Incorporated

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