| mmusic | P. Yue |
| Internet-Draft | Huawei Technologies |
| Intended status: Standards Track | October 21, 2011 |
| Expires: April 23, 2012 |
RTSP Extension for Substream Control
draft-yue-mmusic-rtsp-substream-control-extension-00
This document defines extensions to RTSP 2.0 protocol, including header "Substream", feature tag "Play.substream" , and related new status codes. These extensions enables the playback control of a media stream on substream basis.
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Single Session Transmission (SST) is recommended for the SVC ( Scalable Video Codec) video transport [RFC6190] and MVC (Multiview Video Codec) video transport [I-D.ietf-payload-rtp-mvc] . In SST, a single RTP session conveys all the related media data, namely all the bitstream components. A bitstream component here is part of a media stram that has a common property which could be:
In such a SST session,one or several bitstream components together may be decodable by themselves and therefore make sense to the receiver. These bitstream component(s) combinations are here called Substream.
In SVC and MVC RTP sessions, such a Substream is identified by an Operation Point.
There are cases that a client wants to retrieve a specific substream in such a SST session. However, in the current RTSP 2.0 protocol, the control of the media is on media stream basis, e.g. as an RTP session when RTP is used. This prevents a client to receive only certain substream(s) from the media.
This memo extends the RTSP 2.0[I-D.ietf-mmusic-rfc2326bis] to establish a substream playback control framework, which enables a client to play a part of a media stream.
This memo also defines the substream usage for SVC and MVC.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
The following terms are used in this document and have specific meaning within the context of this document.
The whole framework includes substream annotation, capability negotiation and substream playback control. This section provides an overview of substream control.
Substream annotation is used to announce identifiers for all substreams available in a media stream. which can be retrieved selectively. It is done through a presentation description, typically using an SDP description. Substream annotation based on SDP is described in this section. Substream annotation based on other formats is out of scope of this document.
In SVC, a substream is described as an operation point, which consists of the bitstream components required to be able to decode a particular dependency_id, quality_id, and temporal_id combination. SVC operation points are described through the sprop-operation-point-info attribute in SDP as defined in [RFC6190].
According to [RFC6190], the value of sprop-operation-point-info consists of a comma-separated list of operation-point-description vectors. Each operation-point-description vector represents a substream. Each operation-point-description vector has ten elements,where the first element layer-ID is the identifier of the operation point. This layer-ID can be taken as the identifier for the SVC substream. Since the layer-ID is optional, it may not be included. In this case, a [dependency-ID, temporal_ID, quality-ID] combination is taken as the identifier instead.
Annocation of MVC substreams is specified in [I-D.ietf-payload-rtp-mvc].
editor notes: pending on the complement of [I-D.ietf-payload-rtp-mvc].
Capability negotiation can be used to negotiate support of substream control between RTSP client and server. It makes use of the RTSP feature tag mechanism defined in RTSP 2.0[I-D.ietf-mmusic-rfc2326bis]. A new feature tag (play.substream) is defined in Section 5.2.
Whenever it has received a media presentation with substream annotation, a substream control capable RTSP client SHALL include play.substream in the SUPPORTED header of the RTSP SETUP request. This indicates that the client is able to control the playback of the media on substream basis.
A 2xx response implies that the server is capable of substream control. A server MAY refuse the request with a 551 "Option not supported" response, with an UNSUPPORT header including play.substream.
The receiving client may try to setup a session without this feature later. This means that the client will not perform substream control and play the media as a whole. In the SVC case, the client will play all the layers in the session, whereas in the MVC case it will play all the views in the session.
In case the session is setup correctly, the client may control the play back on substream basis, including:
After successful set up of an RTSP session, the client may perform substream playback control. The playback of a substream is similar with the normal playback of a session, except that the PLAY request shall contain a "SubstreamCtrl" header with substream type and the substream id corresponding to the substream that the client intends to play. Here the substream id idetifies a specific operation point. The actual definition of the substream id is defined by each substream type.
When more than one media stream are controlled, the header shall further contain Request-URIs for each of the the substreams.
Following is the specification of substream types for SVC and MVC media stream. Specification for other substream type is out of scope of current document and should be registered in IANA, as described in Section 7.4.
When the media stream is an SVC stream as defined in [RFC6190], the substream type shall be "SVC"; The substream id could be either a layer-id or a [dependency-ID, temporal_ID, quality-ID] combination, which comes from an operation-point-description vector.
When the media stream is an MVC stream as defined in [I-D.ietf-payload-rtp-mvc], the substream type shall be "MVC".
For MVC, substream id is...
editor's note: substream id for MVC is pending on the complement of draft-ietf-payload-rtp-mvc-00.
A client should not perform substream play if the server has not indicated support of substream control in an ealier message exchange.
Upon receiving a PLAY request with a "SubstreamCtrl" header, the server SHALL identify the substream(s) according to the id(s) and Request-URI(s) in the request, and then provides the indicated substream(s) after sending a 200 OK response.
If the server doesn't support substream control, it should respond a 551 "Option not supported" response as defined in RTSP 2.0[I-D.ietf-mmusic-rfc2326bis].
If the server supports substream control but the substream type indicated in the "SubstreamCtrl" header is not recognized, it shall response wth a 552 "Substream Type Not Recognizable" response, see Section 5.3.1.
If the server supports substream control but the substream type indicated in the "SubstreamCtrl" header is not recognized, it shall response wth 552 "Substream Type Not Recognizable", see Section 5.3.1.
If a requested media is not allowed to be played on substream basis as requested, the server SHALL respond with a 553 "Substream Control Not Allowed" response, see Section 5.3.2.
If the requested substream id is not valid, the server shall response with 554 "Substream id not valid", see Section 5.3.3.
The pause operation of a substream is identical to the pause operation of a normal session. It is not necessary for the client to include a "SubstreamCtrl" header in the pause request message. However, if the request includes a "SubstreamCtrl" header, it shall list all the substreams are currently played.
If aggregated control is used, it is not allowed to pause only a part of a session. It is also not allowed to pause only a specific substream from a media stream.
This section documentsthe extension to the RTSP 2.0 specification. Specifically Section 5.1 specifies the SubstreamCtrl header, Section 5.2 specifies the substream control feature tag, Section 5.3 specifies the status codes extentions for the substream control feature.
SustreamCtrl header is used to indicate the substream(s) of a media stream that the client intends to play. It contains one or more [stream uri, substream type, substream id] triple.
The syntax is:
substream = "substream:" substream-id * (";" sustream-id)
substream-id = stream-uri "," substream-type "," substream_id
stream-uri = RTSP-URI
substream-type = "SVC" / "MVC" / token
When the substream-type is SVC, the syntax of substream_id is:
substream_id = layer-id /dependency-id "," temporal-id "," quality-id layer-id = "layer_id=" layer_id_value layer_id_value = 1*4DIGIT; 0~2047 dependency-id = "dependency_id=" dependency_id_value dependency_id_value = DIGIT ; 0~7 temporal-id = "temporal_id=" temporal_id_value temporal_id_value = DIGIT ; 0~7 quality-id = "quality_id=" quality_id_value quality_id_value = 1*2DIGIT; 0~15 DIGIT = %x30-39 ; any US-ASCII digit "0".."9"
An example of Substream header is: substream: rtsp://example.com/svc.mp4, SVC, lay-id=1
For the MVC case, the syntax of substream_id is:
editor's notes: pending on the complement of mvc-operation-point-id
HCOLON = *( SP / HT ) ":" SWS SEMI = SWS ";" SVS ; semicolon SWS = [LWS] ; Separating White Space DIGIT = %x30-39 ; any US-ASCII digit "0".."9" COMMA = SWS "," SWS ; comma EQUAL = SWS "=" SWS ; equal
SubstreamCtrl header can be used in PLAY and PAUSE request. Proxies shall not modify this header and pass through to the server.
The following feature-tag is defined in this specification and hereby registered. The change control belongs to the IETF. play.substream: Support of substream control operations for media playback. Applies only for servers.
This clause defines the status code extended for the substream control feature. They are:
The server can not understand the substream type.
The substream specified in the request is not allowed for the media identified by the Request-URI. The response shall include a xxxx header to indicate the substream information.
Editor notes: whether there is a need to return substream information is pending for discussion.
The substream id specified in the request is not valid for the media identified by the Request-URI. The response shall include a xxxx header to indicate the substream information.
Editor notes: whether there is a need to return substream information is pending for discussion.
Editor notes: pending for more discussion.
Registration is requested for the newly defined RTSP header extensions, RTSP status code extensions and RTSP feature tag extensions, according to the instructions in section 22 of the base specification [I-D.ietf-mmusic-rfc2326bis].
This section also sets up a registry for substream type that should be maintained by IANA.
The following feature-tag is defined in this specification and hereby registered according to the section 22.1.2 of the base specification [I-D.ietf-mmusic-rfc2326bis]. The change control belongs to the IETF.
The following RTSP status codes are in defined this specification and hereby registered according to section 22.3.2 of the base specification [I-D.ietf-mmusic-rfc2326bis]. The change control belongs to the IETF.
The following RTSP header is defined in this specification and hereby registered according to section 22.4.2 of the base specification [I-D.ietf-mmusic-rfc2326bis]. The change control belongs to the IETF.
IANA should take the responsibility for the registration of the substream type. A new substream type MUST be registered through an IETF Standards Action. A specification for a new substream type MUST consist of the following items:
This specification registers two substream types: SVC and MVC:
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC6190] | Wenger, S., Wang, Y.-K., Schierl, T. and A. Eleftheriadis, "RTP Payload Format for Scalable Video Coding", RFC 6190, May 2011. |
| [I-D.ietf-mmusic-rfc2326bis] | Schulzrinne, H, Rao, A, Lanphier, R, Westerlund, M and M Stiemerling, "Real Time Streaming Protocol 2.0 (RTSP)", Internet-Draft draft-ietf-mmusic-rfc2326bis-27, March 2011. |
| [I-D.ietf-payload-rtp-mvc] | Wang, Y and T Schierl, "RTP Payload Format for MVC Video", Internet-Draft draft-ietf-payload-rtp-mvc-00, March 2011. |
| [RFC4566] | Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. |