Author: lu_zero Date: Thu Sep 27 01:17:09 2007 New Revision: 506 Log: First commit Added: docs/draft-niedermayer-nut-00.xml Added: docs/draft-niedermayer-nut-00.xml ============================================================================== --- (empty file) +++ docs/draft-niedermayer-nut-00.xml Thu Sep 27 01:17:09 2007 @@ -0,0 +1,276 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [ +<!ENTITY rfc2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"> +]> +<?rfc toc="yes"?> +<?rfc symrefs="yes"?> +<?rfc compact="yes"?> +<?rfc subcompact="no"?> +<?rfc strict="no"?> +<?rfc rfcedstyle="yes"?> +<rfc category="std" docName="" + ipr="full3978"> + <front> + + <title abbrev="NUT Container Format">NUT Multimedia Container File Format + </title> + + <!-- see RFC2223 for guidelines regarding author names --> + + <author fullname="Michael Niedermayer" initials="M" + surname="Niedermayer"> + <organization>FFmpeg</organization> + + <address> + <email>michaelni@gmx.at</email> + </address> + </author> + <author fullname="Luca Barbato" initials="L" role="editor" + surname="Barbato"> + <organization>Politecnico di Torino</organization> + + <address> + <postal> + <street>Corso Duca degli Abruzzi 25</street> + + <city>10135 Torino</city> + + <country>Italy</country> + </postal> + + <email>lu_zero@gentoo.org</email> + </address> + </author> + + <date year="2007" /> + + <area>General</area> + +<!-- <workgroup>AVT Working Group</workgroup> --> + + <keyword>Internet-Draft</keyword> + + <keyword>RTP</keyword> + + <keyword>SCTP</keyword> + + <abstract> + <t>This memo defines a method for efficiently storing generic multimedia + streams so that operation like seeking and recover for error can be + performed with minimal computational cost. Minimal overhead and maximal + extensibility had been considered in the development of the format.</t> + </abstract> + + <note title="Editors Note"> + <t>All references to RFC XXXX are to be replaced by references to the + RFC number of this memo, when published.</t> + </note> + + </front> + + <middle> + <section title="Introduction"> + <!-- It is good practice to echo the abstract in the Introduction, +providing citations here. --> + + <t>NUT is a multimedia container format for storage of audio, video, + subtitles and related user defined streams, it provides exact timestamps + for synchronization and seeking, is simple, has low overhead and can + recover in case of errors in the stream.</t> + <t>This document defines: + <list style="hanging"> + <t> The file format layout + </t> + <t> The common stream interleaving rules + </t> +<!-- <t> A simple provision how to map nut streams to rtp. + </t> --> + </list> + </t> + + <section title="Terminology"> + <t>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 <xref target="RFC2119" />.</t> + <t> This document refers to the following definitions + <list style="hanging"> + <t hangText="pts"> Presentation time of the first frame/sample that + is completed by decoding the coded frame. + </t> + <t hangText="dts"> The time when a frame is input into a + synchronous 1-in-1-out decoder. + </t> + <t hangText="frame"> Minimal unit of information that can be + decoded completely, it is usually holds a full frame video frame, + a group of audio samples or a subtitle line. + </t> + <t hangText="Keyframe"> A keyframe is a frame from which you can + start decoding. + The nth frame is a keyframe if and only if frames n, n+1, ... in + presentation order (that are all frames with a pts >= frame[n].pts) + can be decoded successfully without reference to frames prior n in + storage order (that are all frames with a dts < frame[n].dts). + If no such frames exist (for example due to using overlapped + transforms like the MDCT in an audio codec), then the definition + shall be extended by dropping n out of the set of frames which + must be decodable, if this is still insufficient then n+1 shall + be dropped, and so on until there is a keyframe. + Every frame which is marked as a keyframe MUST be a keyframe + according to the definition above, a muxer MUST mark every frame + it knows is a keyframe as such, a muxer SHOULD NOT analyze future + frames to determine the keyframe status of the current frame but + instead just set the frame as non-keyframe. + </t> + </list> + </t> + </section> + <section title="Syntax Convetions"> + <t> Since NUT heavily uses variable length fields, the simplest way to + describe it is using a pseudocode approach instead of graphical + bitfield descriptions. + </t> + <t> The syntax uses datatypes, tagnames and C-like constructs. </t> + + <section title="Datatypes"> + + <t> + <list style="hanging"> + <t hangText="f(n)"> n fixed bits in bigendian order</t> + <t hangText="u(n)"> Unsigned value encoded in n bits MSB-first</t> + + <t hangText="v"> Unsigned variable length value. + <figure anchor="Variable Length Unsigned Figure" title="Variable + Length Unsigned Value"> + <artwork><![CDATA[ + value=0 + do{ + more_data u(1) + data u(7) + value= 128*value + data + }while(more_data)]]> + </artwork> + </figure> + Values can be encoded using the following logic: the data is in + network order, every byte has the most significant bit used as + flag and the following 7 used to store the value. + The first N bit are to be taken, where N is number of bits + representing the value modulo 7, and stored in the first byte. + If there are more bits, the flag bit is set to 1 and the subsequent + 7bit are stored in the following byte, if there are remaining bits + set the flag to 1 and the same procedure is repeated. <br /> + The ending byte has the flag bit set to 0. + In order to decode it is enough to iterate over the bytes until the + flag bit set to 0, for every byte the data is added to the + accumulated value multiplied by 128. + </t> + <t hangText="s"> Signed variable length value. + <figure anchor="Variable Length Signed Figure" title="Variable + Length Signed Value"> + <artwork><![CDATA[ + temp v + temp++ + if(temp&1) value= -(temp>>1) + else value= (temp>>1)]]> + </artwork> + </figure> + The signed values are encoded as the absolute value multiplied by + 2, positive numbers have 1 subtracted to the value. [FIXME: why not + just shift&sign] + </t> + <t hangText="vb"> Variable length binary data (or utf-8 string). + <figure anchor="Variable Length String Figure" title="Variable + Length Signed Value"> + <artwork><![CDATA[ + length v + for(i=0; i<length; i++){ + data[i] u(8) + }]]> + </artwork> + </figure> + Strings and binary data can be encoded basically writing the byte + count as a Variable Length Unsigned Value and the the string. + The strings MUST be encoded in utf-8 + </t> + <t hangText="t"> Universal timestamp. + <figure anchor="Universal Timestamp" title="Variable + Length Timestamp"> + <artwork><![CDATA[ + tmp v + id= tmp % time_base_count + value= (tmp / time_base_count) * time_base[id]]]> + </artwork> + </figure> + [FIXME] + </t> + </list> + </t> + + </section> + + </section> + </section> + + <section title="NUT file layout"> + + <t></t> + + <section title="High level File structure"> + <t>[TODO]</t> + </section> + <section title="Main Header"> + <t>[TODO]</t> + </section> + <section title="Reserved Headers"> + <t>[TODO]</t> + </section> + <section title="Stream Header"> + <t>[TODO]</t> + </section> + <section title="Info Packet"> + <t>[TODO]</t> + </section> + <section title="Index"> + <t>[TODO]</t> + </section> + <section title="Syncpoint"> + <t>[TODO]</t> + </section> + </section> + + <section title="Interleaving Rules"> + </section> + + <section title="IANA Considerations"> + <t>[TODO] In order to comply with IESG policy as set forth in + http://www.ietf.org/ID-Checklist.html, every Internet-Draft that is + submitted to the IESG for publication MUST contain an IANA + Considerations section. </t> + + </section> + + <section title="Security Considerations"> + <t>[TODO]</t> + </section> + + <section title="Acknowledgements"> + <t>Thanks to Marshall Rose for developing the XML2RFC format.</t> + + </section> + </middle> + + <back> + + <references title="Normative References"> + + &rfc2119; + + <!-- <t>[TODO]: Add your own normative references.</t>--> + </references> + + <references title="Informative References"> + + <!-- <t>[TODO] Add your own informative references</t>--> + </references> + </back> +</rfc> +<!-- vim: set sw=2 sts=2 et tw=79: -->