[Mp4-tech] [audio; system] What if PCE disagrees with MP4/ADTS header?

[Ralph Sperschneider]

Mark RISON wrote:
>>> In the case of MP4, what happens if the audioObjectType or
>>> samplingFrequencyIndex in the DecoderSpecificInfo for MPEG-4 AAC files
>>> differ from the object_type or sampling_frequency_index in the PCE at
>>> the end of the GASpecificConfig, where the channelConfiguration is 0?
>>> Which one wins?
>>> Ditto ADTS.
>>>       
>> this looks to me like an invalid configuration.
>>     
>
> OK, well what about the following files in 14496-4-A24:
> a9-aac-samplegroups-edit.mp4
> a7-tone-oddities.mp4
> a4-tone-fragmented.mp4
> a6_tone_multifile.mp4
> a3b-tone-deprot.mp4
> LargerThan4GB.mp4
> ?
>
> They all seem to have an audioObjectType of LC in the DSI, but an
> object_type of SSR in the PCE.
>
> [I also note that they seem to have "dribble" after the PCE.]
>
> Mark
>
>   

I am not familiar with these files, but if your observation is true than 
this looks as it would need to be corrected.

I assume you have noticed that the encoding is different in the PCE:

0 - AAC Main
1 - AAC LC
2 - AAC SSR
3 - AAC LTP

whereas it is in the ASC:

1 - AAC Main
2 - AAC LC
3 - AAC SSR
4 - AAC LTP

So if "2" is used in both cases (as your observation indicates), the 
encoder implementation being used to generate these sequences might have 
had a little shortcoming.

Best,
Ralph

-- 
Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 6167
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