Structure

Purpose

• Try to get a clean, extensible structure to streaming audio
Factors
• Presentation format
• Transport mechanism
• Push/pull
• Content description
• Mechanisms
  • Interfaces declaring types (e.g. WAV interface)
  • Methods returning values (e.g. getContentType())
  • Entries (e.g. Name("Pink Floyd"))

Presentation

• Many presentation types
  • WAV
  • MP3
  • Ogg Vorbis
• Many subtypes e.g. 16-bit, little-endian, stereo, sampling at 48kbits/sec

Transport

• Many transport mechanisms
  • TCP
  • RTP
  • HTTP
• QOS subtypes generally not known

Push/pull

• A push source knows its sink, and writes to it
• A push sink must make available an OutputStream
• A pull sink knows its source, and reads from it
• A pull source must make available an InputStream

Content description

Indefinitely many ways of expressing this

• Artist: Sinead O'Connor
  CD: I do not want what I haven't got
  Track: Feel so different
  Track #: 1
• FM station: RRR
  Program:
  Time:

Interfaces

• Good way of giving type information
• Extensible - just add new interfaces
• Can add multiple types for orthogonal properties
• Won't handle a larger variety of types

Methods

• General method to give info
• Return type is fixed
• Return type non-extensible?

Entries

• Arbitrary info can be passed
• Can be dynamically changed
• Useful for non-essential information

Independent client

A client that doesn't want to bother with any details would just want to see sources and sinks

Transport independent

If the push source or pull sink don't want to get involved in the transport mechanism, they can leave that to the corresponding sink/source

A typical implementation would do

Transport dependent

• A (pull) source can say what transport mechanisms it can support
• These can be specified by interfaces
  • HttpSource
• An HttpSource can return a URL except this can hold any protocol (http, file, ftp, etc)
• An HttpURL is a wrapper around a URL that ensures the protocol is http
• A sink can check from the transport interface if it supports the transport protocol and can get an InputStream for that protocol
  

Presentation

• To a first approximation, the presentation type can be described by an interface
  • presentation.WAV
  • presentation.Ogg
  These are (initially) "place-holder" interfaces
• The presentation type should be orthogonal to transport
• ??? How to handle JMF: MP3 over RTP at only 2.4 kbps, WAV at any speed over HTTP ???

Http/Wav Source

Flexible pull sink

• A flexible pull sink will handle
  • A variety of transport type
  • A variety of presentation formats
• The transport part gets an InputStream
• The presentation part takes the InputStream and "records" it