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OBD:SNDD: Difference between revisions
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:For an overview of the IMA ADPCM algorithm and IMA4 header (if interested), see [https://wiki.multimedia.cx/index.php/Apple_QuickTime_IMA_ADPCM HERE] | :For an overview of the IMA ADPCM algorithm and IMA4 header (if interested), see [https://wiki.multimedia.cx/index.php/Apple_QuickTime_IMA_ADPCM HERE] | ||
::The IMA4 ADPCM data has 34-byte blocks (in the case of stereo, there is an even number of such blocks, because Left and Right blocks are interleaved). | ::The IMA4 ADPCM data has 34-byte blocks (in the case of stereo, there is an even number of such blocks, because Left and Right blocks are interleaved). | ||
::The first two bytes of each block are used to set the initial | ::The first two bytes of each block are used to set the initial predictor (upper 9 bits) and step (lower 7 bits) for decoding the block's samples. | ||
::The other 32 bytes consist of 64 samples stored as nibbles (half-bytes). In the case of stereo, all the nibbles in a block belong to the same channel (either all Left or all Right). | ::The other 32 bytes consist of 64 samples stored as nibbles (half-bytes). In the case of stereo, all the nibbles in a block belong to the same channel (either all Left or all Right). | ||
::Unlike for MS ADPCM, incomplete trailing blocks (if any) are not announced in any way: the final blocks are stored in their entirety, with no way to tell how much of it is actual data. | ::Unlike for MS ADPCM, incomplete trailing blocks (if any) are not announced in any way: the final blocks are stored in their entirety, with no way to tell how much of it is actual data. | ||