diff --git a/src/sniffer.rs b/src/sniffer.rs
index 401a7b1..87922c0 100644
--- a/src/sniffer.rs
+++ b/src/sniffer.rs
@@ -87,3 +87,72 @@ loop{
 BLOCK_DEMO_HEADER:
 //timeline of loading maps, player equipment, bots
 */
+struct PhysicsInputInstructionDeltaState{
+	mouse_pos:glam::IVec2,
+	time:crate::integer::Time,
+}
+
+//everything must be 4 byte aligned, it's all going to be compressed so don't think too had about saving less than 4 bytes
+//8B - 24B
+fn write_input_instruction<W:std::io::Write>(state:&mut PhysicsInputInstructionDeltaState,w:&mut W,ins:&crate::instruction::TimedInstruction<crate::physics::PhysicsInputInstruction>){
+	let dt=ins.time-state.time;
+	//TODO: insert idle instruction if gap is over u32 nanoseconds
+	//OR: end the data block! the full state at the start of the next block will contain an absolute timestamp
+	w.write(&(dt.nanos() as u32).to_le_bytes());//4B
+	let parity=match &ins.instruction{
+		crate::physics::PhysicsInputInstruction::SetMoveRight(true)
+		|crate::physics::PhysicsInputInstruction::SetMoveUp(true)
+		|crate::physics::PhysicsInputInstruction::SetMoveBack(true)
+		|crate::physics::PhysicsInputInstruction::SetMoveLeft(true)
+		|crate::physics::PhysicsInputInstruction::SetMoveDown(true)
+		|crate::physics::PhysicsInputInstruction::SetMoveForward(true)
+		|crate::physics::PhysicsInputInstruction::SetJump(true)
+		|crate::physics::PhysicsInputInstruction::SetZoom(true)=>1u32<<31,
+		crate::physics::PhysicsInputInstruction::SetMoveRight(false)
+		|crate::physics::PhysicsInputInstruction::SetMoveUp(false)
+		|crate::physics::PhysicsInputInstruction::SetMoveBack(false)
+		|crate::physics::PhysicsInputInstruction::SetMoveLeft(false)
+		|crate::physics::PhysicsInputInstruction::SetMoveDown(false)
+		|crate::physics::PhysicsInputInstruction::SetMoveForward(false)
+		|crate::physics::PhysicsInputInstruction::SetJump(false)
+		|crate::physics::PhysicsInputInstruction::SetZoom(false)
+		|crate::physics::PhysicsInputInstruction::ReplaceMouse(_,_)
+		|crate::physics::PhysicsInputInstruction::SetNextMouse(_)
+		|crate::physics::PhysicsInputInstruction::Reset
+		|crate::physics::PhysicsInputInstruction::Idle=>0u32,
+	};
+	//instruction id packed with game control parity bit.  This could be 1 byte but it ruins the alignment
+	w.write(&(ins.instruction as u32|parity).to_le_bytes());//4B
+	match &ins.instruction{
+		crate::physics::PhysicsInputInstruction::ReplaceMouse(m0,m1)=>{//16B
+			let dm0=m0.pos-state.mouse_pos;
+			w.write(&(dm0.x as i16).to_le_bytes());
+			w.write(&(dm0.y as i16).to_le_bytes());
+			w.write(&((m0.time-ins.time).nanos() as u32).to_le_bytes());
+			let dm1=m1.pos-m0.pos;
+			w.write(&(dm1.x as i16).to_le_bytes());
+			w.write(&(dm1.y as i16).to_le_bytes());
+			w.write(&((m1.time-m0.time).nanos() as u32).to_le_bytes());
+			state.mouse_pos=m1.pos;
+		},
+		crate::physics::PhysicsInputInstruction::SetNextMouse(m)=>{//8B
+			let dm=m.pos-state.mouse_pos;
+			w.write(&(dm.x as i16).to_le_bytes());
+			w.write(&(dm.y as i16).to_le_bytes());
+			w.write(&((m.time-state.time).nanos() as u32).to_le_bytes());
+			state.mouse_pos=m.pos;
+		},
+		//0B
+		crate::physics::PhysicsInputInstruction::SetMoveRight(_)
+		|crate::physics::PhysicsInputInstruction::SetMoveUp(_)
+		|crate::physics::PhysicsInputInstruction::SetMoveBack(_)
+		|crate::physics::PhysicsInputInstruction::SetMoveLeft(_)
+		|crate::physics::PhysicsInputInstruction::SetMoveDown(_)
+		|crate::physics::PhysicsInputInstruction::SetMoveForward(_)
+		|crate::physics::PhysicsInputInstruction::SetJump(_)
+		|crate::physics::PhysicsInputInstruction::SetZoom(_)
+		|crate::physics::PhysicsInputInstruction::Reset
+		|crate::physics::PhysicsInputInstruction::Idle=>(),
+	}
+	state.time=ins.time;
+}
\ No newline at end of file