Network Working Group Ross Finlayson INTERNET-DRAFT LIVE.COM Expires: February 5, 2004 October 5, 2004 Interoperability of the "audio/mpa-robust" RTP Payload Format Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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 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 Abstract In order for the "audio/mpa-robust" RTP payload format specification to advance from Proposed Standard to Draft Standard, it is required to demonstrate interoperability for all functionality described by the specification. This document describes the interoperability shown between different implementations of this specification. 1. Introduction The "audio/mpa-robust" RTP payload format for MP3 audio is described in RFC 3119 [3119] (and updated in [3119BIS] to correct typographical errors). This payload format is an alternative to the format described in RFC 2250 [2250], and performs better if there is packet loss. This RTP payload format specification is currently at Proposed Standard. In order to advance to Draft Standard, the Internet standards process [2026] requires "at least two independent and interoperable implementations from different code bases," and that interoperability be shown for "all of the options and features of the specification." This document describes the interoperability shown between three independent implementations: 1/ "LIVE.COM Streaming Media" project's "testMP3Streamer" application [LIVEMEDIA]. 2/ RealNetworks' "RealPlayer 9" media player [REAL]. 3/ The "MPEG4IP" project's "mp4player" media player [MPEG4IP]. (Despite its name, this player plays MP3 audio in addition to MPEG-4 formats.) 2. Features Tested for Interoperability RTP payloads conforming to this specification can vary in the following ways: 1/ Descriptor size. As specified by the "T" (descriptor type) flag in each ADU descriptor, the descriptor size can be either 1 byte (for ADU frame sizes < 64), or 2 bytes. 2/ Fragmentation. If an "ADU frame" is too large to fit within a RTP packet, it is fragmented across more than one RTP packet (each beginning with an ADU descriptor. The fragmentation is indicated by the "C" (continuation) flag in each ADU descriptor. 3/ Interleaving. The high-order 11 bits of each MPEG header ('syncword') can either remain at 0xFFE - which indicates that no ADU frame interleaving is performed - or it can consist of an "Interleaving Sequence Number" - which indicates that ADU frames are rearranged in an interleaving pattern. As described in the next section, we demonstrated interoperability by testing each combination of these three variables. 3. Test Results The results of the interoperability tests are shown in the table below. In each case, the LIVE.COM "testMP3Streamer" application was used as the transmitter, and one (or both) of the "RealPlayer 9" and MPEG4IP "mp4player" applications was used as the receiver. +-----------------+----------------+---------------++------+-----------+ | Stream Features || Receiver | +-----------------+----------------+---------------++------+-----------+ | descriptor size | fragmentation? | interleaving? || Real | mp4player | +-----------------+----------------+---------------++------+-----------+ | 1 byte | no | no || Yes | Yes | | 1 byte | no | yes || Yes | Yes | | 1 byte | yes | no || No | Yes | | 1 byte | yes | yes || No | Yes | | 2 bytes | no | no || Yes | Yes | | 2 bytes | no | yes || Yes | Yes | | 2 bytes | yes | no || No | Yes | | 2 bytes | yes | yes || No | Yes | +-----------------+----------------+---------------++------+-----------+ Note: As noted in the table, "RealPlayer 9" was unable to handle fragmented ADU frames. However, because "mp4player" was able to play fragmented frames from the LIVE.COM "testMP3Streamer" application, this is sufficient to demonstrate interoperability of this feature between two independent implementations. 4. Security Considerations Not applicable. 5. Normative References [3119] Finlayson, R., "A More Loss-Tolerant RTP Payload Format for MP3 Audio," RFC 3119, June 2001. [2026] Bradner, S., "The Internet Standards Process -- Revision 3," RFC 2026, October 1996. 6. Informative References [3119BIS] Finlayson, R., "A More Loss-Tolerant RTP Payload Format for MP3 Audio," draft-ietf-avt-rfc3119bis-02.txt, Work in progress, February 2004. [2250] Hoffman, D., Fernando, G., Goyal, V. and M. Civanlar, "RTP Payload Format for MPEG1/MPEG2 Video", RFC 2250, January 1998. [LIVEMEDIA] "LIVE.COM Streaming Media," Live Networks, Inc., . [REAL] RealNetworks, Inc., . [MPEG4IP] The "MPEG4IP Open Streaming Video and Audio" project, . 7. Author's Address Ross Finlayson, Live Networks, Inc. (LIVE.COM) 650 Castro St., suite 120-196 Mountain View, CA 94041 EMail: finlayson (at) live.com WWW: http://www.live.com/ 8. IPR Notice The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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