[FFmpeg-devel] [PATCH] AAC decoder

Steven Ellis mail_lists
Thu Apr 10 02:53:14 CEST 2008


Baptiste Coudurier wrote:
> Hi,
>
> Steven Ellis wrote:
>
>> On Wed, April 2, 2008 20:51, Nico Sabbi wrote:
>>
>>> On Wednesday 02 April 2008 10:37:42 Baptiste Coudurier wrote:
>>>
>>>> Hi,
>>>>
>>>> Nico Sabbi wrote:
>>>>
>>>>> On Wednesday 02 April 2008 08:08:40 Andreas ??man wrote:
>>>>>
>>>>>> Steven Ellis wrote:
>>>>>>
>>>>>>> On Wed, April 2, 2008 02:56, Andreas ??man wrote:
>>>>>>>
>>>>>>>> Andreas ??man wrote:
>>>>>>>>
>>>>>>>>> Hi
>>>>>>>>>
>>>>>>>>> Here is the AAC decodoer from the soc repo.
>>>>>>>>>
>>>>>>>> .. and here is an updated version with mpeg4audio.[ch] stuff.
>>>>>>>>
>>>>>>> Any chance this will handle the LATM encapsulated AAC audio that
you can get in DVB broadcasts?
>>>>>>>
>>>>>> Nope, I believe that should be added in the AAC parser.
>>>>>>
>>>>> in mplayer's libfaad there's already the necessary LATM Parser,
although in a reasonably simplified version (only the 2 most common
situations are handled)
>>>>>
>>>> Is LATM prefered over ADTS in DVB ? Why is that ?
>>>>
>>> I wouldn't say it's preferred, also because being LATM a bitstream
syntax brain-farted to carry multiple streams it doesn't make the
slighest sense in mpeg-ts.
>>> It's one more of the possible syntaxes allowed to carry AAC, and the
worst of all if you ask me, but still it's used in Norway and New
Zealand.
>>>
>> Some of the updated DVB specs I've read appear to mandate the use of
LATM for HE-AAC over DVB.
>>
>
> This will need a clear quote from the specs :>
>

Sorry if this is a repost, had some mail issues

Refernced from -

http://wiki.ebu.ch/bgav/images/4/4e/Tm1214r27.avc0075r15.2.dTS101154V1.7.1.doc

Annex H (informative):
Guidelines for the Implementation of MPEG-4 High Efficiency AAC and High
Efficiency AAC v2 Audio in DVB Compliant Transport Streams

H.3    DVB Compliant Streams

The MPEG-4 HE AAC or  HE AAC v2 elementary stream data shall be first
encapsulated in the LATM multiplex format according to ISO/IEC 14496-3
[17]. The AudioMuxElement() multiplex element format shall be used. The
LATM formatted MPEG-4 HE AAC or  HE AAC v2 elementary stream data shall be
encapsulated in the LOAS transmission format according to ISO/IEC 14496-3
[17]. The AudioSyncStream() version shall be used. AudioSyncStream() adds
a sync word to the audio stream to allow for synchronization.

The LATM/LOAS formatted MPEG-4 HE AAC or  HE AAC v2 elementary stream data
shall be encapsulated in PES packets. The MPEG-4 HE AAC PES shall be
carried with an MPEG stream_id = 110x xxxx and a stream type
assignment of 0x11 as described in ITU???T Rec. H.222.0 | ISO/IEC
13818???1 [1]. No alignment is required. More than one audio unit is
allowed per PES packet. If a PTS is present in the PES header it shall
refer to the first audio frame that follows the first syncword that
commences in the PES packet.

When an MPEG-4 HE AAC or  HE AAC v2 stream is included in a DVB
transport stream, the AAC_descriptor shall also be included. The
AAC_descriptor is located in the PMT and the Selection Information Table
of the DVB SI Tables defined in EN 300 468 [6].



Is that a clear enough quote?

Steve







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