[Mp4-tech] RE: [mpam] Re: LATM
Rob Koenen (MPEGIF)
rob.koenen mpegif.org
Wed Feb 16 21:22:43 ESTEDT 2005
And what's the answer for non-MPEG members?
Rob
> -----Original Message-----
> From: mpam-admin uow.edu.au [mailto:mpam-admin uow.edu.au] On
> Behalf Of Ralph Sperschneider
> Sent: Tuesday, 15 February, 2005 17:23
> To: Philipp Kraetzer
> Cc: mp4-tech lists.mpegif.org; mpam uow.edu.au
> Subject: [mpam] Re: LATM
>
> Dear Philipp,
>
> MPEG meanwhile addressed this issue. Assuming you being an
> MPEG member, please
> check out what we drafted in N7022. Note that this is still
> in a proposal stage.
>
> Best regards,
>
> Ralph
>
> Philipp Kraetzer wrote:
> > Ralph, thanks for your answers.
> >
> > The case that muxConfigPresent=0 is maybe not that rare when the
> > StreamMuxConfig() is defined out-of-band using e.g. SDP. In
> this case,
> > the optional SDP parameter 'cpresent' corresponds to
> muxConfigPresent
> > and might be set to 0. I do not completely understand why
> the standard
> > does not allow a flexible number of AAC frames for each
> AudioMuxElement
> > without changing the StreamMuxConfig().
> >
> > In the case that muxConfigPresent=1 I appreciate your
> proposal for a
> > corrigendum in case the nobody else has another solution. A
> byte-aligned
> > insertion of the "raw" AAC data into the LATM layer would
> simplify the
> > implementation, and would allow hinting AAC tracks in
> MP4/3GPP files to
> > create RFC3016 compliant streams.
> >
> > I found further discussion on this topic in an older IMTC document
> > (October 23, 2002, "IMTC,Packet-Switched Streaming, Activity Group,
> > Implementation Guide") which might be of interest
> > "
> >
> >
> > /2.3// MPEG4-Audio-AAC-LATM/SDP: is streamMuxConfig
> allowed inband ?/
> >
> > * *
> >
> >
> >
> > According to RFC3016 for audio streamMuxConfig can be sent
> inband RTP
> > or outband in the SDP description. The advantage of outband
> transmission
> > is having a secure transmission of the parameters and bit
> shifting of
> > audio data can be avoided (streamMuxConfig is not byte aligned in
> > inband mode). The advantage of inband transmission is the
> possibility to
> > change parameters of streamMuxConfig during transmission.
> >
> >
> >
> > SA4 approved the following solution due to following CRs (
> >
> > Tdoc S4-020349, Tdoc S4-020348):
> >
> >
> >
> > ”Configuration information is mandated to be sent in the
> SDP (which is
> > transported over TCP and thus safely delivered to the terminal) for
> > MPEG4 audio and MPEG4 video.”
> >
> > "
> > and
> > "
> >
> >
> > /2.11 MPEG4-Audio-AAC-LC/RFC3016 : “last
> audioMuxElement containing
> > fewer packets than signalled allowed ?”/
> >
> > *(new)*
> >
> >
> >
> > when streaming AAC under the ‘cpresent=0’ restriction, you cannot
> > reconfigure the number of frames per audioMuxElement during
> streaming.
> > This may present a problem at the end of the stream, since
> the final
> > audioMuxElement (completed in the last RTP packet) might
> need to contain
> > fewer AAC frames than originally configured at start of
> streaming. The
> > issue would ask for some clarification on how to handle this.
> >
> >
> >
> > Suggestion for a solution :
> >
> > Send a request to IETF and/or MPEG-4 Audio for a solution.
> >
> >
> >
> > *On discussion*
> >
> > "
> >
> > Any further hints or suggestions are very welcome.
> >
> > Thanks,
> > Philipp
> >
> > -----Ursprüngliche Nachricht-----
> > Von: Ralph Sperschneider
> [mailto:ralph.sperschneider iis.fraunhofer.de]
> > Gesendet: Freitag, 26. November 2004 11:27
> > An: Philipp Kraetzer
> > Cc: mp4-tech lists.mpegif.org; 'mpam uow.edu.au'
> > Betreff: Re: LATM
> >
> > Philipp Kraetzer wrote:
> >
> >>I correct my posting from yesterday - sorry for confusion:
> >>
> >>I have two issues with LATM as defined in 14496-3 Amd. 1
> (MPEG-4 Audio).
> >>
> >>1) A LATM packet always contains n AAC frames where n is
> equal to the
> >>numSubFrames field in the StreamMuxConfig. If
> MuxConfigPresent is set
> >>to 0 the configuration cannot change during transmission
> and all LATM
> >>packets must contain the same number of AAC frames. How can
> I transport
> >>a stream containing m AAC frames where m is no multiple of
> >>numSubFrames? Do I have to do some padding in the last LATM packet?
> >>
> >>
> > If you really use a configuration with muxConfigPresent=0,
> then your
> > assumption is correct. This would however only make sence
> in a closed
> > system, where all the parameters usually specified in the
> > StreamMuxConfig() are pre-defined.
> > All the sync-streams specified by MPEG pre-configure
> muxConfigPresent=1.
> >
> >>2) If MuxConfigPresent is 1 the LATM packet may start with the
> >>StreamMuxConfig which does not seem to be octet-aligned.
> Does this mean
> >>that I have to shift all of the following bytes of the AAC frames
> > repectively?
> >>
> >>
> > This is tru just in the case you need those bytes in a byte-aligned
> > fashion. Even without the StreamMuxConfig() you would have
> to deal with
> > the useSameStreamMux flag.
> >
> >>Even worse, I want to create a MP4 file with a hint track for a
> >>standard AAC
> >>(non-LATM) track. The hint track shall create a LATM stream
> for RFC3016
> >>compliant streaming. The hint track syntax allows the
> insertion of data
> >>from the sample descriptor but only an integer number of bytes. I
> >>cannot see how to create a valid LATM packet
> (AudioMuxElement) from the
> >>descriptor data (the StreamMuxConfig) and the ES data if the
> >>StreamMuxConfig is not octet-aligned.
> >>
> >>
> > Well, I don't see a simple solution for that kind of problem. Does
> > anyone else do? In case this is urgently needed one could
> consider to
> > correct this by means of a corrigendum for
> audioMuxVersion=1, which is
> > not yet used up to my knowledge. The syntax could then look like:
> >
> > if (muxConfigPresent) {
> > useSameStreamMux;
> > if (!useSameStreamMux)
> > StreamMuxConfig();
> > if ( audioMuxVersion = 1 )
> > ByteAlign();
> > }
> >
> > Any suggestion is welcome.
> >
> > Ralph
> >
>
> --
> Dipl.-Ing. Ralph Sperschneider | Phone: +49 9131 776 344
> Fraunhofer IIS | Fax: +49 9131 776 67 344
> Am Wolfsmantel 33 |
> mailto:ralph.sperschneider iis.fraunhofer.de
> D 91058 Erlangen | http://www.iis.fraunhofer.de/amm/
>
>
>
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