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Can AAC change sampling rate w/in file/stream? Do decoders support it?, [was “AAC Frequency transition” subt. “AAC” in General Audio/TOS #6]
post Aug 27 2013, 11:58
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AAC encoded data can come in many container formats . Like Mp4 ,adts etc., . In any of these are the sampling rates allowed to change inbetween a file ?If so are there any decoders which support it ?
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post Aug 27 2013, 17:32
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The sampling rate is fixed at encode time.

However for aac-he files a decoder can optionally downsample by 2 if it does not support he. This is because he files are actually encoded at half sample rate and then upsampled by the decoder to the original rate.
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post Aug 28 2013, 19:25
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Also note that lossy encoders only encode as little as possible, so even if a sample rate was 192KHz, but there was only audio (or a lowpass filter) under 16000 Hz then that would be effectively the same as a sampling rate of 32KHz.
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