1– Introduction To Direct Show

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Introduction to DirectShow - 1

Windows Media Streaming Architecture


Intel - Motivation & Goals

DirectShow is the most common architecture for:

•STB and IP-STB media streaming and broadcast reception

•PC Streaming Goals•Understand STB architecture, its

advantages and disadvantages•Fast prototyping and application building

for testing and demonstrations


What is DirectX•DirectX is Microsoft's component based

architecture for media processing.•Similar streaming architecture were

designed by:▫Real ▫Emblaze (RapidMedia)▫Linux (GStreaming)

•Media processing ▫Audio▫Video▫Transport streams▫text.


DirectX – Why we need it?•Software reusability

▫Code blocks can be reused and inherited▫Common Interfaces

•Easy connection between 3rd party modules

•Which components?▫Compression▫color conversion▫audio effects▫Transport stream handlers


BACKGROUND

DirectX Evolution from proprietary Codec to Filter base architecture


VFW• VFW architecture – a Plug-In

architecture that supported CODEC and CAPTURE Interfaces for Audio & Video stream manipulation.

• Advantages – All the CODECs have the same interfaces. There is no need specific modifications for each codec

Capture CODEC

Control Interfaces

IO Interfaces


VFW Problems Rigid architectureRigid architecture OnlyOnly three types of filters three types of filters How to add costume filters that split or How to add costume filters that split or

mux transport stream?mux transport stream? Rigid interfaces creates a problem to the Rigid interfaces creates a problem to the

future progress of the architecturefuture progress of the architecture


Active Movie•A Filter base architecture that support

customize filters•The architecture is built using:

▫Filters that manipulates the stream▫Pins that handle filter connection ▫graph management which

Connect the filters (automatically) Manage filters states (run, pause, stop) Transfer messages between filters


DirectX•Evolution of Active Movie (Audio & Video)

to other aspects:▫DirectShow – (previously ActiveMovie)

Audio/Video/Text.▫DirectDraw/Direct3D – Graphics.▫DirectSound – Sound effects and 3D sound.▫DirectPlay/DirectInput – Multiplayer Game

tools.▫DirectMusic – Automatic music generation


INTRODUCTION TO DIRECTSHOW

Hands-on DirectShow : GraphEdit


GraphEdit

•Visual Interface for graph building and testing.


GraphEdt – Rendering a file•Render a media file•The graph build is what the OS does when

you double-click on a file.•File rendering options:

▫Drag a media file to graph edit▫Use File->Open File▫Use:

graph->Insert filters use the circled button as a short cut

Select File Source Async. Right click on output pin and select render


GraphEdt - Play with it

•Use the: Play, Pause, and Stop commands▫Notice the file progress bar

•Use the slider to change the current play position


GraphEdit – A bit more• Try looking at filter properties:• Use right-click on the filter and select

“Filter Properties”• We will later look at the Interface that

enables the communication to property pages.

• Example of Source file property• This property is used only for monitoring

and not for controls. Why?


The Translator video• Lets view it using Graphedt Media\Metargemet.wmv• This video is a nice example for information

processing architecture• The information is:

▫ Generated at the source (Keren)▫ Processed and translated by a “transform unit” (Riki –

translator)▫ Rendered to the students▫ Feedback messages are passed from the Renderer to the

source via the translator

TeacherInfo. Source

Smart Student“Transform”

Student“Renderer"


DirectShow Basic ideas

•Information processing is a sequential process

•Each processing unit has a clear function•The Source “Push” or pump information to

processing units (Blue). Data information is always Unidirectional: “Downstream”

•Feedback is sent from the Renderer(s) to the source (Orange) – “Upstream”

•No Information loops

Source

“Transform” “Renderer"


Information passing architecture

•There are basically two methods:▫Push ▫Pull

•Those architecture differ in ▫threading, ▫Which filter is the active filter▫Where is the “Brain” of the graph


Push Architecture

•Source is active•Source generate Media Samples•information is pushed by the source •Like in the case of the “Metargemet”•Source is active, owns the “processing

thread”•Used in

▫ASF/WMA/WMV files▫Video capture (USB cam, video cards)▫BDA capture


Pull Architecture•Information is pulled by a non-source filter•Source is passive•Does not own the “processing thread”•In most file processing schemes (AVI,

MPEG2) the source is “dumb” and passive and the parser (demuxer) holds the “knowledge” of file parsing.


Components required•Data Processing unit– used for:

▫Media data Generation▫Media data manipulation/transform▫Media data rendering

•Interfaces – Generic Interfaces between data processing units ▫In “Metargemet” we use “Air Interface” with

two basic media descriptors•Media descriptors

▫In “Metargemet” we use two media types: Archaic speech media between Source and Transform “Sleng” between Transform (Riki) and Renderer

(Student)•Management unit (in “Translator” –

class/school)


Naming•Data processing unit = Filter

▫Used for data manipulation and transform.•Filter Interface = Pin

▫Used to define the connection between filters

▫Include information about: Direction Memory required Media Type


Naming - 2

•Media Descriptor = Media Type▫Include information about the media passed

•Data Unit = Media Sample▫Include the data itself▫Include information about the data


Filters•ActiveX objects

▫(Use COM Interfaces)•Manipulates data•Have Pin as members for interfacing other

filters•Three basic types: Source, Render,

Transform •Identification: GUID•Control – property pages


Pin

• Filters have one or more IO Interfaces - pins• Pin is a class which basically holds interfaces to

which connect processing modules (filters)• Pins could be exposed or hidden

▫ Look at Infinite Pin tee filter▫ Dynamic creation of pins for many types of filters:

Infinite Pin T MPEG and AVI Splitters

• Two basic type: ▫ Input ▫ Output


Graph Builder•Create a streaming process for example:

▫Read from file▫Demux▫Decode▫Encode▫Stream to network

•Tasks:▫Loads the filters▫connect Filters▫Change filter states▫Disconnect filters▫Remove filters from graph.

•The graph is always unidirectional (No loops)

•Have three basic states: Play, Pause, Stop.


DMOs

•DirectX® Media Objects (DMOs) •Create stream processing object that

could operate without a graph (Filters could only work as part of a graph)

•DMOs could operate inside a graph using a “DMO Wrapper” which acts as a filter

•Advantage▫Simpler interface▫No need to create a graph


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