At a 48-kHz sample rate, for example, a WMA Pro sync frame contains enough data to play for 2048 ticks of the sample clock (42.67 milliseconds). Each sync frame contains its own header and can be decoded independently of the other sync frames in the stream. WMA Pro and AC-3 are both compressed non-PCM formats that transmit digital audio streams in units called synchronization frames. Pass-through transmission does not require the S/PDIF sending and receiving ports to understand the encoding of the non-PCM stream. The principle of S/PDIF pass-through transmission is that a non-PCM data stream can pass through an S/PDIF link as though it were a PCM stream. The Sony/Philips digital interface (S/PDIF) format is defined primarily for transmitting PCM audio data, but it can easily be adapted to transmit non-PCM data.
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