[FFmpeg-soc] [PATCH]aacsbr: internal sample rate

[Alex Converse]

Fs_SBR as defined by the specification is the SBR internal sample rate
and defined to be twice the core coder nominal sample rate (listed in
Table 4.82 - Sampling Frequency Mapping). ExtensionSamplingFrequency
is the SBR output sample rate.

The code currently uses ExtensionSamplingFrequency instead of Fs_SBR.
This patch creates a new context variable to hold Fs_SBR.

Caveats:
*This doesn't support sample rates that are not nominal sample rates,
however AFAIK FFmpeg's LC/Main decoder does not support them either.
There are no official LC/Main test vectors for them.
*This probably doesn't handle the 7350 Hz sample rate properly as 7350
is not listed in the table so presumably the nominal sample rate is
8000. FFmpeg does support AAC @ 7350 Hz. There are no official LC/Main
test vectors for it, however I hacked one up. MPEG seems to have zero
interest in this sample rate outside of scalable profiles, however it
still appears to be legal in the mainstream profiles. [1]

Ref:
[1] http://lists.mpegif.org/pipermail/mp4-tech/2009-February/008661.html
http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/2009-February/061946.html
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