AVT Working Group M. Xu Internet-Draft CS. Zheng Intended status: Informational T. Jiang Expires: February 25, 2010 WX. Zhang JP. Zhang Digital Wave Co., Ltd August 24, 2009 RTP Payload Format for DRA Audio draft-xu-avt-dra-00 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on February 25, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Xu, et al. Expires February 25, 2010 [Page 1] Internet-Draft DRA-RTP Format August 2009 Abstract The present document describes a RTP packaging scheme for DRA compressed audio data transmission, as well as the corresponding RTP payload format. According to the properties of DRA compressed audio frame and the Maximum Transmission Unit (MTU) of network, the scheme provides 3 packaging modes for different coding and transmission requirements. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 3. Overview of DRA . . . . . . . . . . . . . . . . . . . . . . . 3 4. RTP Payload Format . . . . . . . . . . . . . . . . . . . . . . 4 4.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . . 4 4.2. Structure of the RTP DRA Payload Format . . . . . . . . . 5 5. SDP related information for DRA Audio . . . . . . . . . . . . 6 5.1. Media Type Registration . . . . . . . . . . . . . . . . . 7 5.2. SDP Format for DRA audio . . . . . . . . . . . . . . . . . 8 5.2.1. Attributes (a=) . . . . . . . . . . . . . . . . . . . 8 5.2.2. Media Description(m=) . . . . . . . . . . . . . . . . 9 5.2.3. Examples . . . . . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10 8.2. Informative References . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Xu, et al. Expires February 25, 2010 [Page 2] Internet-Draft DRA-RTP Format August 2009 1. Introduction DRA multi-channel digital audio coding technology is capable of preserving high fidelity sounds over limited storage and limited transmission bandwidth, suitable for a wide variety of application areas including digital audio broadcasting, digital TV accompany sound, home theater, Internet streaming media, and personal media player. In the fields of IP network transmission and real-time broadcasting, Real-Time Transport Protocol, as described in RFC 3550 [RFC3550], can be employed for transmission and synchronization of DRA audio streams. This document describes an RTP payload format for transmitting audio data compressed by DRA technology . 2. Requirements Language 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 RFC 2119 [RFC2119]. 3. Overview of DRA DRA digital audio coding technology keeps 24-bit precision (except deliberating quantization loss)for all channels. Its supported channel configurations include commonly known stereo, 5.1 , 6.1, and 7.1 surround sound, besides a large space reserved for future audio development (maximum 64.3 surround sound). DRA can handle standard sampling frequencies spanning from 8kHz to 192kHz, including 44.1kHz and 48kHz. There is no explicit restriction on DRA encoding bitrate, which is determined by the channel bandwidth and audio quality requirement. DRA has a fixed input frame length of 1024 samples for encoding, thus its time duration can be calculated according to sampling rate. Bit count for encoded frame is controlled by encoding configuration parameters, which are recorded in the frame header. Figure 1 illustrates the structure of a DRA encoded frame described in "Specification for multichannel digital audio coding technology" (China national standard) [GB/T 22726-2008]. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sync Word|Header|normal ch data|LFE ch data|error check|ancillary| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: DRA Frame Structure Xu, et al. Expires February 25, 2010 [Page 3] Internet-Draft DRA-RTP Format August 2009 Every audio frame starts with the sync word 0x7fff, then frame header. Figure 2 illustrates parts of the header structure. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |frame type |audio data frame length| other header information | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: DRA Frame Header's Structure Frame type: 1 bit, '0' for normal frame header, '1' for extension header. Audio data frame length: 10 bits (normal frame header) or 13 bits (extension header), representing the length from the sync word to the error check word, counting in unit of 32-bit. 4. RTP Payload Format DRA encoded frame length varies with sampling rate and bitrate, and possibly overruns the Maximum Transmission Unit (MTU) in high bitrate modes. In this case, a single audio frame is parted to several blocks. On the other hand, DRA supports Variable Bit-Rate (VBR) encoding, allocating bit resources according to perceptible information in each frame. Therefore, within the limit of MTU, several short audio frames are packaged into one RTP packet for higher transmission efficiency. 3 RTP DRA payload formats are employed: o Single-Frame packet: RTP payload comprising a single complete DRA compressed frame; o Multi-Frame Packet: RTP payload comprising multiple complete DRA compressed frame; o Frag-Frame Packet: RTP payload comprising a fragment of one DRA compressed frame. Subsection 4.2 has detailed description of the above 3 modes. 4.1. RTP Header Usage The usage of RTP header information specified in this document observes the RTP header information defined inRFC 3550 [RFC3550]. Figure 3 gives the RTP header format for the reader's convenience. Xu, et al. Expires February 25, 2010 [Page 4] Internet-Draft DRA-RTP Format August 2009 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|X| CC |M| PT | sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | synchronization source (SSRC) identifier | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | contributing source (CSRC) identifiers | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: RTP Header according to RFC 3550 Marker bit (M): 1 bit Set to '1' only if at least one complete audio frame or the last block of an audio frame contained in the current RTP packet. Payload type (PT): 7 bits DRA RTP packet payload type designation is not discussed in the present document. Its is set by the RTP profile of DRA RTP payload format, or dynamically set. TimeStamp (timestamp): 32 bits The timestamp of RTP is used to record the sampling time of the first audio frame in the current RTP packet. For DRA RTP payload, the clock frequency corresponding to the time stamp is equal to the audio sampling frequency. If the current RTP packet comprises more than one DRA audio frame, the sampling time for each audio frame can be derived from the time stamp plus the accumulated audio frame duration time. In Frag-Frame Packet mode, all RTP packets belong to the same audio frame should have the same time stamp. 4.2. Structure of the RTP DRA Payload Format RTP DRA payload comprises a 16-bit payload header and audio frame data. Only the latter vary among the 3 RTP packaging modes. Figure 4 illustrates the payload structure of the Multi-Frame Packet mode. Xu, et al. Expires February 25, 2010 [Page 5] Internet-Draft DRA-RTP Format August 2009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload Header | DRA frame 1 | DRA frame 2 | ... DRA frame n| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Multi-Frame Packet RTP payload structure The payload header structure is given in figure 5. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |PM | MBZ | N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: RTP payload header structure Packaging Mode (PM): 2 bits Indicating the current RTP packaging modes, as is shown in table 1: +----------+---------------------+ | PM value | Mode | +----------+---------------------+ | 0 | Single-Frame Packet | | 1 | Multi-Frame Packet | | 2 | Frag-Frame Packet | | 3 | Forbidden | +----------+---------------------+ Table 1: Packaging Mode Must Be Zero (MBZ, reserved): 6 bits Reserved for future use, all 6 bits must be set to '0' Number (N, block serial number or frame number): 8 bits If PM = 1, or Multi-Frame Packet mode, 'Number' is set to the number of DRA frames in the current RTP packet; if PM = 2, 'Number' is set to the serial number of the current block in a DRA audio frame; if PM = 0, 'Number' is set to '1'. 5. SDP related information for DRA Audio Xu, et al. Expires February 25, 2010 [Page 6] Internet-Draft DRA-RTP Format August 2009 5.1. Media Type Registration This section uses the template provided in RFC 4288 [RFC4288] and follows RFC 4855 [RFC4855]. o MIME media type name: audio o MIME subtype name: vnd.dra o Required parameters: rate: The RTP timestamp clock rate is equal to one of the audio sampling rates. The sampling rates consist of 13 possible values as specified in Table 10 of GB/T 22726-2008 [GB/T 22726-2008]: 8000 Hz, 11025 Hz, 12000 Hz, 16000 Hz, 22050 Hz, 24000 Hz, 32000 Hz, 44100 Hz, 48000 Hz, 88200 Hz, 96000 Hz, 176400 Hz, 192000 Hz. o Optional parameters: none o Encoding considerations: Transport_provided This media type is framed and contains binary data. o Security considerations: See section 7 of this document. o Interoperability considerations: None o Published specification: This specification and see GB/T 22726-2008 [GB/T 22726-2008]. o Applications which use this media type: Audio and audio for video can be multi-channel audio compressed with this media type. o Additional information: Magic number(s): The first 16 bits of an DRA frame are fixed as synchronization word, which is 0x7FFF in hex expression. o Person & email address to contact for further information: Jiang Tian Xu, et al. Expires February 25, 2010 [Page 7] Internet-Draft DRA-RTP Format August 2009 o Intended usage: COMMON o Author/Change controller: XU Mao, et al. 5.2. SDP Format for DRA audio Only the channel number and the sampling rate information are needed besides raw DRA bitstream defined in GB/T 22726-2008 [GB/T 22726-2008] for decoding. Both will be present in SDP defined in RFC 4566 [RFC4566]to assist decoding. But there is no explicit configuration information embedded. 5.2.1. Attributes (a=) a. First, a short item.a=maxptime: This is an optional parameter, found by: = *8*1000 /. The maximum packet size is confined by Maximum Transmission Unit (MTU). b. a=rtpmap: / [/] This is a required attribute, where = 97, defined in RFC 3551 [RFC3551], dynamically assigned = "dra" = DRA audio sampling rate = channel number c. a=fmtp: This is a optional attribute used if and only if the < format specific parameters> is not empty, where = = 97, currently includes only bitrate=# Xu, et al. Expires February 25, 2010 [Page 8] Internet-Draft DRA-RTP Format August 2009 where "#" is an integer bitrate in bps. 5.2.2. Media Description(m=) m= / This is a required field, where = "audio" = 58636 or any available even numbered port = number of RTP sessions, only used for multiple sessions = "RTP/AVP" = = 97. 5.2.3. Examples This section provides two examples of the SDP data for DRA as follows: a. 48000Hz, stereo DRA bitstream: m=audio 58636 RTP/AVP 97 a=rtpmap:97 dra/48000/2 b. 320kbps, 44100Hz, 5.1 channel DRA bitstream, two sessions: m=audio 58800/2 RTP/AVP 97 a=rtpmap:97 dra/44100/6 a=fmtp:97 bitrate=320000 6. IANA Considerations A new media subtype has been assigned for DRA by IANA; see Section 5.1. Xu, et al. Expires February 25, 2010 [Page 9] Internet-Draft DRA-RTP Format August 2009 7. Security Considerations The payload format described in this document is subject to the security considerations defined in RFC 3550 [RFC3550]. Confidentiality protection would have to be applied, so as to protect the users' provacy and contents with copyright. 8. References 8.1. Normative References [GB/T 22726-2008] You et al., "Specification for multichannel digital audio coding technology", Dec, 2008. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC4855] Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, February 2007. 8.2. Informative References [RFC2736] Handley, M. and C. Perkins, "Guidelines for Writers of RTP Payload Format Specifications", BCP 36, RFC 2736, December 1999. [RFC4184] Link, B., Hager, T., and J. Flaks, "RTP Payload Format for AC-3 Audio", RFC 4184, October 2005. Xu, et al. Expires February 25, 2010 [Page 10] Internet-Draft DRA-RTP Format August 2009 Authors' Addresses Mao Xu Digital Wave Co., Ltd Room 2002A, Building B, Cyber Tower, No.2, ZhongGuanCun South Avenue Beijing, 100031 China Phone: +86-10-5278-6263 Email: xumao@digitalwave.cn ChuSheng Zheng Digital Wave Co., Ltd Room 2002A, Building B, Cyber Tower, No.2, ZhongGuanCun South Avenue Beijing, 100031 China Phone: +86-10-5278-6263 Email: zhengcs@digitalwave.cn Tian Jiang Digital Wave Co., Ltd Room 2002A, Building B, Cyber Tower, No.2, ZhongGuanCun South Avenue Beijing, 100031 China Phone: +86-10-5278-6263 Email: jiangt@digitalwave.cn WeiXiong Zhang Digital Wave Co., Ltd Room 2002A, Building B, Cyber Tower, No.2, ZhongGuanCun South Avenue Beijing, 100031 China Phone: +86-10-5278-6263 Email: zhangwx@digitalwave.cn Xu, et al. Expires February 25, 2010 [Page 11] Internet-Draft DRA-RTP Format August 2009 JingPing Zhang Digital Wave Co., Ltd Room 2002A, Building B, Cyber Tower, No.2, ZhongGuanCun South Avenue Beijing, 100031 China Phone: +86-10-5278-6263 Email: zhangjp@digitalwave.cn Xu, et al. Expires February 25, 2010 [Page 12]