diff --git a/src/tests.rs b/src/tests.rs
index 1e44e2a..d9c1da7 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -8,13 +8,15 @@ fn _1()->Result<(),crate::v1::Error>{
 	println!("header={:?}",bot_file.header);
 	for &TimedBlockId{time,block_id} in &bot_file.header.offline_blocks_timeline{
 		println!("offline time={} block_id={:?}",time,block_id);
-		let block=bot_file.data.read_block(&bot_file.header,block_id)?;
+		let block_info=bot_file.header.block_info(block_id)?;
+		let block=bot_file.data.read_block_info(block_info)?;
 		// offline blocks include the following event types:
 		// World, Gravity, Run, Camera, Setting
 	}
 	for &TimedBlockId{time,block_id} in &bot_file.header.realtime_blocks_timeline{
 		println!("realtime time={} block_id={:?}",time,block_id);
-		let block=bot_file.data.read_block(&bot_file.header,block_id)?;
+		let block_info=bot_file.header.block_info(block_id)?;
+		let block=bot_file.data.read_block_info(block_info)?;
 		// realtime blocks include the following event types:
 		// Input, Output, Sound
 	}
diff --git a/src/v1.rs b/src/v1.rs
index 6762578..7e8415b 100644
--- a/src/v1.rs
+++ b/src/v1.rs
@@ -342,6 +342,20 @@ pub struct FileHeader{
 	#[br(count=num_realtime_events)]
 	pub realtime_blocks_timeline:Vec<TimedBlockId>,
 }
+pub struct BlockInfo{
+	start:u32,
+	length:u32,
+}
+impl FileHeader{
+	pub fn block_info(&self,block_id:BlockId)->Result<BlockInfo,Error>{
+		if self.block_positions.len() as u32<=block_id.0{
+			return Err(Error::InvalidBlockId(block_id));
+		}
+		let start=self.block_positions[block_id.0 as usize];
+		let end=self.block_positions[block_id.0 as usize+1];
+		Ok(BlockInfo{start,length:end-start})
+	}
+}
 
 pub struct File<R:BinReaderExt>{
 	pub header:FileHeader,
@@ -363,17 +377,12 @@ impl<R:BinReaderExt> FileData<R>{
 	fn data_mut(&mut self)->&mut R{
 		&mut self.data
 	}
-	fn block_reader(&mut self,header:&FileHeader,block_id:BlockId)->Result<binrw::io::TakeSeek<&mut R>,Error>{
-		if header.block_positions.len() as u32<=block_id.0{
-			return Err(Error::InvalidBlockId(block_id))
-		}
-		let block_start=header.block_positions[block_id.0 as usize] as u64;
-		let block_end=header.block_positions[block_id.0 as usize+1] as u64;
-		self.data.seek(std::io::SeekFrom::Start(block_start)).map_err(Error::Seek)?;
-		Ok(self.data_mut().take_seek(block_end-block_start))
+	fn block_reader(&mut self,block_info:BlockInfo)->Result<binrw::io::TakeSeek<&mut R>,Error>{
+		self.data.seek(std::io::SeekFrom::Start(block_info.start as u64)).map_err(Error::Seek)?;
+		Ok(self.data_mut().take_seek(block_info.length as u64))
 	}
-	pub fn read_block(&mut self,header:&FileHeader,block_id:BlockId)->Result<Block,Error>{
-		let data=self.block_reader(header,block_id)?;
+	pub fn read_block_info(&mut self,block_info:BlockInfo)->Result<Block,Error>{
+		let data=self.block_reader(block_info)?;
 		let block=Block::read(data).map_err(Error::InvalidData)?;
 		Ok(block)
 	}