Something like this?
Select Top 1000000 Coalesce(Cast(tblVideoController.CurrentHorizontalResolution
As nvarchar), 'unknown') As Horizontal,
Coalesce(Cast(tblVideoController.CurrentVerticalResolution As nvarchar),
'unknown') As Vertical,
Count(tblAssets.AssetID) As Counted
From tblVideoController
Inner Join tblAssets On tblVideoController.AssetID = tblAssets.AssetID
Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
Inner Join tsysOS On tblAssets.OScode = tsysOS.OScode
Where tblAssetCustom.State = 1
Group By Coalesce(Cast(tblVideoController.CurrentHorizontalResolution As
nvarchar), 'unknown'),
Coalesce(Cast(tblVideoController.CurrentVerticalResolution As nvarchar),
'unknown')
Order By Horizontal Desc,
Vertical Desc