read/write blockiert nach select

[OnlyFoo]

das folgende programm bleibt ständig bei "write data to encoder..." stehen, obwohl select versichert haben sollte, dass das nicht passieren kann...
hat jemand ne idee, woran das liegen könnte?

$read = array();
			
			#adding read fd if we need data
			if( sizeof( $buffer_input ) < 1024 )
				$read[] = $input;
			
			if( sizeof( $buffer_output ) < 1024 )
				$read[] = $mencoder[ 'output' ];
			
			# adding write fd if we have data
			$write = array();
			
			if( sizeof( $buffer_output ) )
				$write[] = $client;
			
			if( sizeof( $buffer_input ) )
				$write[] = $mencoder[ 'input' ];
			
			#select
			$rc = stream_select( $read, $write, $ex = NULL, 5, 0 );
			if( $rc === false ) {
				echo "error doing select\n";
				break;
			}
			if( $rc === 0 ) {
				echo "no data in 5 seconds, try again";
				$error++;
				continue;
			}
			
			$error = 0;
			if( in_array( $input, $read ) ) {
				echo "read input from source...\n";
				
				$buffer_input[] = fread( $input, 4096 );
			}
			
			if( in_array( $mencoder[ 'output' ], $read ) ) {
				echo "read data from encoder...\n";
				
				$buffer_output[] = fread( $mencoder[ 'output' ], 4096 );
			}
			
			if( in_array( $client, $write ) ) {
				echo "write data to the client\n";
				
				if( !fwrite( $client, array_shift( $buffer_output ) ) )
					break;
				
				fflush( $client );
			}
			
			if( in_array( $mencoder[ 'input' ], $write ) ) {
				echo "write data to encoder...\n";
				
				if( !fwrite( $mencoder[ 'input' ], array_shift( $buffer_input ) ) )
					break;
				
				fflush( $mencoder[ 'input' ] );
			}