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codec-utils: support extension audio object type and sample rate

Alex Ashley requested to merge alexashley/gst-plugins-base:issue39-support-heaac into master

ISO 14496-3 defines that audioObjectType 5 is a special case that indicates SBR is present and that an additional field has to be parsed to find the true audioObjectType.

There are two ways of signaling SBR within an AAC stream - implicit and explicit (see [1] section 4.2). When explicit signaling is used, the presence of SBR data is signaled by means of the SBR audioObjectType in the AudioSpecificConfig data.

Normally the sample rate is specified by an index into a table of common sample rates. However index 0x0f is a special case that indicates that the next 24 bits contain the real sample rate.

[1] https://www.telosalliance.com/support/A-closer-look-into-MPEG-4-High-Efficiency-AAC

Fixes #39 (closed)

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