refactor spec

1 files changed, 49 insertions, 21 deletions

diff --git a/evc/spec.md b/evc/spec.md
index 77f6b7d..f35128d 100644
--- a/evc/spec.md
+++ b/evc/spec.md
@@ -1,4 +1,32 @@
-# The Experimental Video Codec
+# Low-Efficiency Video Codec
+
+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.
+
+## 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.
+
+## Advanced-Reference-Block
+
+Like Reference-Block but instead translates by non-integer amount of pixels,
+applying a 2x2 matrix from the center of the block and multiplying the color
+value of each component, interpolating if necessary.
+
+## Compressed-Literal-Block
+
+_**JPEG? just DCT? idk**_
 
 ## File format
 
@@ -6,27 +34,27 @@
 - resolution: _`u16, u16`_
 - frame count: _`u64`_
 - frames (repeated [frame count]-times)
-  - block type
-  - block
-    - 0 **Literal-Block** (pixels saved)
-      - pixels: _`[[u8; 3]]`_
-    - 1 **Split-Block** (delegated to 2 sub-blocks split on the longest axis)
+  - block kind: _`u8` (see tags below)_
+  - block: _one of the following_
+    - 0 **Literal-Block**
+      - pixels: _`[[u8; 3]; (inferred)]`_
+    - 1 **Compressed-Literal-Block**
+      - length: _`u32`_
+      - data: _`[[u8; length]`_
+    - 2 **Split-Block**
       - sub-blocks: _`[block; 2]` (see above)_
-    - 2 **Reference-Block** (reuses previous frame in some way)
+    - 3 **Reference-Block**
       - translation: _`i8, i8`_
-    - 3 **Advanced-Reference-Block** (reuses previous frame in some way)
-      - translation: _`s8, s8`_ (translation encoded as _floats_)
-      - transform: _`s8, s8, s8, s8`_ (2x2-matrix of _floats_ applied before
-        sampling)
-      - value_scale: _`i8`_ (represents multiplication of each color component
-        with $1.05^n$)
-
-### _`s8`_
-
-8-bit scalar. When read as _`i8`_ represents a value of $\frac{x}{|x|} *
-\sqrt{2}^{|{x}| - 4}$ for $x \neq 0$, otherwise 0.s
+    - 4 **Advanced-Reference-Block**
+      - translation: _`s8, s8`_ (translation)
+      - transform: _`s8, s8, s8, s8`_ (2x2-matrix applied before sampling
+        relative to the center)
+      - value_scale: _`i8`_ (multiplication of each color component by $1.05^n$)
 
-### Todo
+### Data Types
 
-- JPEG compress Literal-Blocks
-- general compression (gzip oder so)
+- _`u<n>`_: unsigned n-bit integer (little-endian)
+- _`i<n>`_: signed n-bit integer using twos-complement (little-endian)
+- _`s8`_: 8-bit scalar. When read as _`i8`_ represents a value of
+  $\frac{x}{|x|} * \sqrt{2}^{|{x}| - 4}$ for $x \neq 0$, otherwise 0
+- _`[<T>; <N>]`_: Array of T with length N