[FFmpeg-devel] [PATCH] AAC: ADTS profile_ObjectType to MPEG-4 AOT

[Alex Converse]

On Thu, Feb 12, 2009 at 8:37 AM, Robert Swain <robert.swain at gmail.com> wrote:
> 2009/2/12 Alex Converse <alex.converse at gmail.com>:
>> On Wed, Feb 11, 2009 at 9:55 PM, Alex Converse <alex.converse at gmail.com> wrote:
>>> From ISO/IEC 14496-3:2005/1.A.4.3 Audio Data Transport Stream (ADTS)
>>> "this element denotes the MPEG-4 Audio Object Type
>>> (profile_ObjectType+1) according to the table defined in subclause
>>> 1.5.2.1."
>>>
>>> This is needed to decode Main profile streams in ADTS that use
>>> anything outside of the LC feature set.
>
> "The interpretation of this data element depends on the value of the
> ID bit. If ID is
> equal to '1' this field holds the same information as the profile
> field in the ADTS
> stream defined in ISO/IEC 13818-7. If ID is equal to '0' this element
> denotes the
> MPEG-4 Audio Object Type (profile_ObjectType+1) according to the table defined
> in subclause 1.5.2.1."
>
> As noted for one of the other patches (the ADTS encoder patch IIRC),
> "If ID is equal to '0'". I notice that the ID is not parsed but
> skipped at the moment. We should parse it and adhere to its
> behavioural connotations as in the spec.
>

Right now we are lenient toward decoding files marked as MPEG-2 that
use MPEG-4 AAC features (e.g. PNS) as long as the feature is simply
marked as reserved in MPEG-2 land and not interpreted as something
else.

Looking at the table:

profile_ObjectType | MPEG2 profile (ID=1) | MPEG-4 AOT (ID=0)
0                  | Main Profile         | AOT AAC MAIN (=1)
1                  | Low Complexity Profi | AOT AAC LC (=2)
2                  | Scalable Sampling Ra | AOT AAC SSR (=3)
3                  | (reserved)           | AOT AAC LTP (=4)

The only case where they differ (3) the MPEG-2 version is undefined.

>> It appears the list at the message.
>
> It didn't, I received the first as well.
>

It didn't make it to the archive.
http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/2009-February/062212.html

Regards,
Alex