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diff --git a/bv1/spec.md b/bv1/spec.md new file mode 100644 index 0000000..ca30a39 --- /dev/null +++ b/bv1/spec.md @@ -0,0 +1,45 @@ +# BOMedia Video 1 + +The codec compresses image sequences by avoiding redundancies by reusing parts +of previous frames. A frame is one block that is then subdivided further as +needed. + +## Literal-Block + +Stores the pixels' RGB values as is. + +## Split-Block + +Delegates to two sub-blocks. The block is split orthorgonally on the longest +axis. If needed, the left/top block is rounded down and the right/bottom rounded +up. + +## Reference-Block + +Indicates that parts of the last frame are reused. The data reused is at the +position of this block in the last frame with the translation added. + +## File format + +- magic bytes: `5e b1 c3 08` +- resolution: _`u16, u16`_ +- frame count: _`u64`_ +- frames (repeated [frame count]-times): Frame (see below) + +## Frame format + +- block kind: _`u8` (see tags below)_ +- block: _one of the following_ + - 0 **Split-Block** + - sub-blocks: _`[block; 2]` (see above)_ + - 1 **Literal-Block** + - pixels: _`[[u8; 3]; (inferred)]`_ (stored line-by-line) + - 2 **Reference-Block** + - position_offset: _`[i8; 2]`_ + - color_offset: _`[i16; 3]`_ + +### Data Types + +- _`u<n>`_: unsigned n-bit integer (little-endian) +- _`i<n>`_: signed n-bit integer using twos-complement (little-endian) +- _`[<T>; <N>]`_: Array of T with length N |