sbr: fix parameter resolution in VBR mode and transient normalization - #178
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When running in VBR quality mode (-q), hEncoder->config.bitRate is 0, causing SbrUpdate() to default to low amplitude and coarse frequency resolutions (bs_amp_res = 0, dk = 2). Derive an effective nominal stream bitrate from quantqual when bitRate is 0 so HE-AAC uses fine resolution parameters. Also update SbrAnalyze() to normalize transientStrength using the total slot count (num_slots) rather than the decimated count (sampled), preventing transient strength scaling artifacts during decimation.
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These are correctness fixes. Neutral performance.
When running in VBR quality mode (-q), hEncoder->config.bitRate is 0, causing SbrUpdate() to default to low amplitude and coarse frequency resolutions (bs_amp_res = 0, dk = 2). Derive an effective nominal stream bitrate from quantqual when bitRate is 0 so HE-AAC uses fine resolution parameters.
Also update SbrAnalyze() to normalize transientStrength using the total slot count (num_slots) rather than the decimated count (sampled), preventing transient strength scaling artifacts during decimation.