discussion of the Creative Commons Metadata work

["J.C. De Martin" <demartin AT polito.it>]

Dear all,

We (academic research group) have been working
on streaming since 2000.
As a natural extension of that effort, plus
our being an Affiliate Institution for iCommons Italy,
we have become quite involved in streaming of
metadata information - CCPL metadata being
our first concern.

We are now ready to propose a simple standard
for the streaming of metadata information.
The attached document (html + PNG figure)
contains two proposals:

#1: to use of SDP for streaming metadata description;
#2: to use of a RTSP DESCRIBE response to
      send the SDP metadata from streaming server to client.

The two proposals are already implemented and working
as part of our free software suite of streaming server and
client - the Open Media Streaming project -
which is fully compliant with IETF protocols (RTP/RTCP
and RTSP), and available at http://streaming.polito.it.

If our proposal is found solid and adopted by other
streaming software, interoperability (a constant
problem with streaming applications) could be
finally extended also to the domain of metadata.

We are eager to hear your feedback!

Thanks,

Juan Carlos De Martin

--
I migliori saluti, 


Juan Carlos De Martin
______________________________________
Principal Research Scientist
IEIIT
Consiglio Nazionale delle Ricerche
Politecnico di Torino
Corso Duca degli Abruzzi, 24
10129 Torino, Italy
E-mail: demartin AT polito.it
Tel: +39-011-564-5421
Fax: +39-011-564-5429
http://media.polito.it

DRAFT

Proposal to Support Creative Commons Licensing Metadata

Within IETF-compliant Streaming Applications

J.C. De Martin, D. Quaglia, G. Mancini, F. Varano, M. Penno, F. Ridolfo

Internet Media Group

Politecnico di Torino/IEIIT-CNR

http://media.polito.it

Torino (Italy), 2^nd August 2004

Document URL:

http://streaming.polito.it/streamingMetadataProposal.html

Abstract

This work presents two proposals regarding streaming metadata, and, in particular, Creative Commons licensing metadata. The first proposal makes the case for the use of the Session Description Protocol (SDP) for streaming metadata description; regarding CCPL metadata, we propose two new dedicated SDP attributes, uriLicense and uriMetadata. The second proposal regards the case of streaming over IP networks using the IETF Real-Time Streaming Protocol (RTSP): in that case, we propose to exchange the SDP-metadata within a DESCRIBE RTSP message. A reference implementation of the two proposals is available as part of the Open Media Streaming free software suite (http://streaming.polito.it).

1. Background: The Session Description Protocol (SDP)

The Session Description Protocol (SDP) [1] is a text-based Internet protocol for the description of multimedia sessions for announcement, invitation, and other forms of multimedia session initiation. SDP is designed to convey the information needed to setup a new session but it is not intended to support negotiation of session content or media encoding modes. SDP can be delivered through different transport protocols including the Session Announcement Protocol (SAP) [2], the Session Initiation Protocol (SIP) [3], the Real-Time Streaming Protocol (RTSP) [4], the electronic mail using the MIME extensions, and the Hypertext Transport Protocol.

An SDP session description consists of a number of lines of text of the form <type>=<value>. The field <type> is always exactly one character and is case-significant. The field <value> is a structured text string whose format depends on <type>. In general <value> is either a number of fields delimited by a single space character or a free format string. Examples of mandatory pairs are: v=(protocol version), o=(owner/creator and session identifier), s=(session name). An optional pair is a=(attributes), which can be used to extend the set of information conveyed by SDP.

2. Proposal #1: Streaming Metadata Description Using SDP

We propose to add the support for streaming metadata using SDP.

For the specific case of Creative Commons Licensing Metadata, we propose to define the following two new SDP attributes:

a=uriLicense:License URI

a=uriMetadata:URI pointing to metadata

The first attribute reports one of the URIs defined by the Creative Commons Commitee [6]. The second attribute refers to a place to find metadata about the resource, which may include other information besides the license, e.g., title, creator's name, and copyright holder.

The defined attributes exploit the standard extension mechanism of the SDP grammar and, therefore, their formal specification (e.g., through the Augmented Backus-Naur Form) is omitted. These SDP attributes may be transmitted to the client in several fashions as described above. They can be displayed to the user in a human-readable form or used by search engines to index the multimedia content. If the client does not understand metadata attributes, it should simply ignore such attributes, as required by the SDP standard.

In the following Sections the second part of the proposal is presented. A reference implementation of a streaming architecture is described in which SDP descriptions containing Creative Commons licensing metadata are transported through the Real-Time Streaming Protocol (RTSP) and, in particular, as a response to the DESCRIBE command.

3. Background: The Real-Time Streaming Protocol (RTSP)

The Real-Time Streaming Protocol (RTSP) [4] is is an application-level text-based Internet protocol to control the delivery of real-time data, such as audio and video. Sources of data can include both live data feeds and stored clips. This protocol is intended to control multiple data delivery sessions and provide a means for choosing delivery channels such as UDP, multicast UDP and TCP. Traditionally, RTSP does not deliver the multimedia streams itself, but it rather acts as a “network remote control”; an RTSP-compliant streaming player can start, pause, and stop the delivery of the multimedia content by sending appropriate commands to a remote streaming server.

Through the DESCRIBE command the client asks the server to send a description of the presentation or media object identified by a Uniform Resource Location (URL); the client uses the “Accept” field of the message to specify which description formats it understands. The server responds with a description of the requested resource. The resource description contains information about the media streams (one or more) that constitute the presentation, such as encoding algorithms, network addresses, and metadata. RTSP does not impose a particular description format for the response to the DESCRIBE command; the streaming architecture proposed in this document uses the Session Description Protocol (SDP) for the server's response.

4. Background: The Open Media Streaming Project

The Open Media Streaming project (OMSP) is a free/libre software project for the development of an open platform for multimedia streaming [5]. The platform is based on the full support of the IETF standards for real-time data transport over the Internet (IP/UDP/RTP-RTCP and RTSP). The aim of the project is to provide a free alternative to the proprietary streaming applications that currently dominate the market.

The current OMSP distribution consists of:

• a server, Fenice;

• a player, NeMeSI;

• a web-based application to publish and schedule multimedia contents over the Internet, Palinsesto.

OMSP uses the Real Time Streaming Protocol (RTSP) to establish and control time-synchronized streams of continuous media such as audio and video.

5. Proposal #2: SDP-Metadata Exchange Using RTSP DESCRIBE

We propose to exchange the SDP streaming metadata proposed in Section 2 by means of a response to a RTSP DESCRIBE command. Other options are coinceivable, using other RTSP messages or RTP/RTCP, but the use of the DESCRIBE command seems the most appropriate both conceptually and practically.

Figure 1 shows the sequence of operations performed by the streaming server and client to transmit and process metadata. The first step consists in the DESCRIBE request sent by the client. The server retrieves metadata locally from the media source description and then sends them as SDP attributes. In the next step the client processes metadata, e.g., title and author are shown to the user and the license attributes are checked against user preferences. If playback is authorized, the client sends a SETUP command, followed by a PLAY request to the server to start the delivery of the multimedia content.

Figure 1. Metadata exchange between server and client.

In the following we report an example of DESCRIBE request and response between client and server:

C->S: DESCRIBE rtsp://localhost/prova.sd RTSP/1.0

CSeq: 1

Accept: application/sdp;

User-Agent: NeMeSI

S->C: RTSP/1.0 200 OK

CSeq: 1

Server: fenice/1.4

Date: Sat, 5 Jun 2004 09:08:32 GMT

Content-Type: application/sdp

Content-Base: rtsp://localhost.localdomain/prova.sd

Content-Length: 222

v=0

o=fenice 3296365950 3296365950

c=IN IP4 127.0.0.1

s=RTSP Session

i=fenice 1.4 Streaming Server

u=prova.sd

t=0 0

m=audio 5004 RTP/AVP 14

a=uriLicense:http://creativecommons.org/licenses/by-nc-sa/1.0/

a=uriMetadata:http://example.com/licenseinfo.html

The above technique is already implemented the Open Media Streaming streaming server and client.

3. Conclusions

We have presented two proposals proposal to describe and exchange metadata, and in particular CCPL licensing metadata, within an IETF-compliant streaming framework. The proposed techniques have been implemented within the Open Media Streaming software suite for the specific case of inclusion of metadata within a RTSP DESCRIBE response. The software is available for download at http://streaming.polito.it.

References

[1] M. Handley and V. Jacobson, “SDP: Session Description Protocol”, RFC 2327, April 1998.

[2] M. Handley, C. Perkins, and E. Whelan, “Session Announcement Protocol (SAP)”, RFC 2974, October 2000

[3] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley and E. Schooler, “SIP: Session Initiation Protocol”, RFC 3261, June 2002.

[4] H. Schulzrinne and A. Rao and R. Lanphier, “Real Time Streaming Protocol (RTSP)”, RFC 2326, April 1998.

[5] http://streaming.polito.it.

[6] http://www.creativecommons.org

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