Originally posted by Vancouver
Products that perform the decoding of lossless bitstreams can have access to all the metadata of the encoded stream, and of course can look at each audio packet within the VBR stream and report its size, and convert that info to peak bitrate if so desired.
When TrueHD lossless is decoded, the PCM output is always a 24 bit word, regardless of the original being 16, 20, 22, 24, or whatever resolution, and the bitstream metadata does not indicate the source resolution, as it is not useful to the decoder. Any unused bits in the 24-bit output will of course be zeros in order to ensure lossless operation. A downstream device will not know what the source resolution was unless it analyzes the zero padding of LSBs. It can directly know the sample rate and number of channels, and from that one can easily compute a bitrate for the PCM. But this bitrate has no relation to the compressed lossless bitrate as that is VBR, changing every few milliseconds.
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