[FFmpeg-devel] [PATCH] AAC decoder

[Steven Ellis]

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 :>
>
>   
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