[VLC] Unbroken streaming in loopback

When reach the step to show below command like below, pls refer below syntax to add the option, gather

Before:

:sout=#duplicate{dst=rtp{sdp=rtsp://:8554/1},dst=display} :sout-keep

After:

:sout=#gather:duplicate{dst=rtp{sdp=rtsp://:8554/1},dst=display} :sout-keep

[C] Pre-define values for array in arbitrary length

For some situations, it is required to pre-define values for array in arbitrary length.
It is related to make use of the pre-processor of limited handling in arbitrary number which I think many experienced programmers have ever suffered from this pain.

Here is a smart method I have ever seen to make use of the binary trick to pre-define values for array in arbitrary length.

#define N    123//length of the array
#define D    4

array[N] =
{
    #if N & 0x1
    D,
    #endif

    #if N & 0x2
    D, D,
    #endif

    #if N & 0x4
    D, D, D, D,
    #endif

    #if N & 0x8
    D, D, D, D, D, D, D, D,
    #endif

    #if N & 0x10
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D
    #endif

    #if N & 0x20
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D,
    #endif

    #if N & 0x40
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D,
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D,
    #endif

    #if N & 0x80
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D,
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D,
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D,
    D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D, D,
    #endif
}


Mathematically, any positive integer can be expressed as a sum of power of 2 series like below

Therefore, we can make use of above trick to create an array of arbitrary length with pre-defined value.

[Computer Science] Fast Integer Division and Modulus

Sometimes, fast integer division or modulus is required for high speed processing.

Division is normally the most uncomfortable operation for general processors.

Thanks to the math, it is able to convert divisions into bit shift operation by a trick.

Below is a proof of the trick, the idea is inspired from the glorious "Hacker's Delight" 

Since Modulus is a set of operations of division and multiplication like below

a%b = a - (a/b)*b

So, modulus can also take advantages from above trick

[VBA]Compact Access Database bypassing create a dummy database

https://github.com/walter426/VbaUtilities/blob/master/AccessObjUtilities.bas

Function to compact Access Database bypassing create a dummy database

'Comapact and renew Database
Public Function CompactAndRenewDb(Db_path As String) As String
    On Error GoTo Err_CompactAndRenewDb
    
    Dim FailedReason As String
    
    If FileExists(Db_path) = False Then
        FailedReason = Db_path
        GoTo Exit_CompactAndRenewDb
    End If

    
    Dim WShell As Object
    Dim FSO As Object
    
    Set WShell = CreateObject("WScript.Shell")
    Set FSO = CreateObject("Scripting.FileSystemObject")


    Dim Db_CP_path As String
    Db_CP_path = WShell.ExpandEnvironmentStrings("%TEMP%") & "\" & FSO.GetBaseName(Db_path) & "_Compacted" & "." & FSO.GetExtensionName(Db_path)

    
    If Len(Dir(Db_CP_path)) > 0 Then
        Kill Db_CP_path
    End If
    
    Call CompactDatabase(Db_path, Db_CP_path)
    
    
    If Len(Dir(Db_CP_path)) = 0 Then
        GoTo Exit_CompactAndRenewDb
    End If
    
    
    Kill Db_path
    Call CopyFileBypassErr(Db_CP_path, Db_path)
    Kill Db_CP_path
    
    
Exit_CompactAndRenewDb:
    CompactAndRenewDb = FailedReason
    Exit Function

Err_CompactAndRenewDb:
    FailedReason = Err.Description
    Resume Exit_CompactAndRenewDb
    
End Function

[VBA]Join two tables with any number of columns in a easy format

https://github.com/walter426/VbaUtilities/blob/master/SqlUtilities.bas
In order to join two tables into one, the SQL syntax is very complicated.
So I wrote below function to reduce the complexity.



''Create table which are joined from two tables
Public Function CreateTbl_JoinTwoTbl(Tbl_src_1_name As String, Tbl_src_2_name As String, JoinCond As String, ColSet_Join_1 As Variant, ColSet_Join_2 As Variant, Tbl_des_name As String, Optional ColSet_src_1 As Variant = Null, Optional ColSet_src_2 As Variant = Null, Optional ColSet_Order As Variant = Null) As String
    On Error GoTo Err_CreateTbl_JoinTwoTbl
    
    Dim FailedReason As String

    If TableExist(Tbl_src_1_name) = False Then
        FailedReason = Tbl_src_1_name & "does not exist!"
        GoTo Exit_CreateTbl_JoinTwoTbl
    End If
    
    If TableExist(Tbl_src_2_name) = False Then
        FailedReason = Tbl_src_2_name & "does not exist!"
        GoTo Exit_CreateTbl_JoinTwoTbl
    End If
    
    If IsNull(ColSet_Join_1) = True Then
        GoTo Exit_CreateTbl_JoinTwoTbl
    End If
    
    If IsNull(ColSet_Join_2) = True Then
        GoTo Exit_CreateTbl_JoinTwoTbl
    End If
    

    DelTable (Tbl_des_name)
    
    
    Dim Col_Idx As Integer
    
    
    With CurrentDb
        If IsNull(ColSet_src_1) = True Then
            Dim RS_Tbl_src As Recordset
            Set RS_Tbl_src = .OpenRecordset(Tbl_src_1_name)
            
            Dim fld_idx As Integer
            Dim fld_name As String
            
            ColSet_src_1 = Array()
            
            With RS_Tbl_src
                For fld_idx = 0 To .Fields.count - 1
                    fld_name = .Fields(fld_idx).name
                    Call AppendArray(ColSet_src_1, Array("[" & fld_name & "]"))
                Next fld_idx
                
                .Close
                
            End With 'RS_Tbl_src
        End If


        If IsNull(ColSet_src_2) = True Then
            Set RS_Tbl_src = .OpenRecordset(Tbl_src_2_name)
            
            With RS_Tbl_src
                Dim NumOfColSet_Join_found As Integer
                NumOfColSet_Join_found = 0
                
                ColSet_src_2 = Array()
                    
                For fld_idx = 0 To .Fields.count - 1
                    fld_name = .Fields(fld_idx).name

                    If NumOfColSet_Join_found <= UBound(ColSet_Join_2) And FindStrInArray(ColSet_Join_2, fld_name) > -1 Then
                        NumOfColSet_Join_found = NumOfColSet_Join_found + 1
                    Else
                        Call AppendArray(ColSet_src_2, Array("[" & fld_name & "]"))
                    End If
                Next fld_idx
    
                .Close
                
            End With 'RS_Tbl_src
        End If
    End With 'CurrentDb
    

    Dim SQL_Seg_Select As String
    SQL_Seg_Select = "SELECT " & "[" & Tbl_src_1_name & "]." & Join(ColSet_src_1, ", [" & Tbl_src_1_name & "].") & ", " & "[" & Tbl_src_2_name & "]." & Join(ColSet_src_2, ", [" & Tbl_src_2_name & "].")

    Dim SQL_Seg_JoinOn As String
    SQL_Seg_JoinOn = "("

    For Col_Idx = LBound(ColSet_Join_1) To UBound(ColSet_Join_1)
        SQL_Seg_JoinOn = SQL_Seg_JoinOn & "[" & Tbl_src_1_name & "].[" & ColSet_Join_1(Col_Idx) & "] = [" & Tbl_src_2_name & "].[" & ColSet_Join_2(Col_Idx) & "] AND "
    Next Col_Idx

    SQL_Seg_JoinOn = Left(SQL_Seg_JoinOn, Len(SQL_Seg_JoinOn) - 4) & ")"

    
    Dim SQL_Seg_OrderBy As String
    SQL_Seg_OrderBy = ""
    
    If IsNull(ColSet_Order) = False Then
        SQL_Seg_OrderBy = "ORDER BY "
        
        For Col_Idx = LBound(ColSet_Order) To UBound(ColSet_Order)
            SQL_Seg_OrderBy = SQL_Seg_OrderBy & "[" & Tbl_src_1_name & "].[" & ColSet_Order(Col_Idx) & "], "
        Next Col_Idx
        
        SQL_Seg_OrderBy = Left(SQL_Seg_OrderBy, Len(SQL_Seg_OrderBy) - 2)
        
    End If
    
    
    Dim SQL_cmd As String
    
    SQL_cmd = SQL_Seg_Select & " " & vbCrLf & _
                "INTO [" & Tbl_des_name & "] " & vbCrLf & _
                "FROM [" & Tbl_src_1_name & "] " & JoinCond & " JOIN [" & Tbl_src_2_name & "] " & vbCrLf & _
                "ON " & SQL_Seg_JoinOn & vbCrLf & _
                SQL_Seg_OrderBy & " " & vbCrLf & _
                ";"

    RunSQL_CmdWithoutWarning (SQL_cmd)


Exit_CreateTbl_JoinTwoTbl:
    CreateTbl_JoinTwoTbl = FailedReason
    Exit Function

Err_CreateTbl_JoinTwoTbl:
    FailedReason = Err.Description
    Resume Exit_CreateTbl_JoinTwoTbl
    
End Function

[VBA] Transfer multiple objects(e.g. tables, queries) in a database

https://github.com/walter426/VbaUtilities

'Transfer multiple objects in a database
Public Function TransferObjSetInDb(TransferType As Variant, DatabaseType As String, DatabaseName As String, ObjectType As Variant, SrcList As Variant, DesList As Variant, Optional StructureOnly As Boolean = False, Optional StoreLogin As Boolean = False) As String
    On Error GoTo Err_TransferObjSetInDb

    Dim FailedReason As String

    If Len(Dir(DatabaseName)) = 0 Then
        FailedReason = DatabaseName
        GoTo Exit_TransferObjSetInDb
    End If
 

    If VarType(DesList) <> vbArray + vbVariant Then
        DesList = SrcList
    End If
 

    If UBound(SrcList) <> UBound(DesList) Then
        FailedReason = "No. of elements in SrcList and DesList are not equal"
        GoTo Exit_TransferObjSetInDb
    End If
 
 
    Dim TblNameIdx As Integer

    For TblNameIdx = 0 To UBound(SrcList)
        If ObjectType = acTable Then
            DelTable (DesList(TblNameIdx))
        ElseIf ObjectType = acQuery Then
            DelQuery (DesList(TblNameIdx))
        End If


        On Error Resume Next
        DoCmd.TransferDatabase TransferType, DatabaseType, DatabaseName, ObjectType, SrcList(TblNameIdx), DesList(TblNameIdx), StructureOnly, StoreLogin
        On Error GoTo Next_TblNameIdx
     
Next_TblNameIdx:
    Next TblNameIdx
 
    On Error GoTo Err_TransferObjSetInDb
 
 
Exit_TransferObjSetInDb:
    TransferObjSetInDb = FailedReason
    Exit Function

Err_TransferObjSetInDb:
    FailedReason = Err.Description
    Resume Exit_TransferObjSetInDb
 
End Function

[Python] Coordinate Transform between Grid and Geographic (e.g HK1980 and WGS84)

https://pypi.python.org/pypi/CoorTransform_GirdGeographic
https://github.com/walter426/Python_CoorTransform_GirdGeographic

It is a python package refer to my previous VBA module, http://waltertech426.blogspot.com/2014/07/vba-coordinate-transform-from-hk1980-to.html.

This python package is to provide functions for coordinate transform from grid to geographic, or vice versa.
Only HK1980 and WGS84 are set as the default conversion.

#Coordinate Transformation according to http://www.geodetic.gov.hk/data/pdf/explanatorynotes_c.pdf

from math import * 


class CoorTransformer_GridAndGeographic:
#HK80 Datum is set as default
def __init__(self, E0 = 836694.05, N0 = 819069.8, Lng0 = 114.178556, Lat0 = 22.312133, m_0 = 1, M0 = 2468395.723, a = 6378388, e2 = 6.722670022 * pow(10,-3)):
#Initilalize Projection Parameter
self.E0 = E0
self.N0 = N0
self.Lng0 = Lng0 * pi / 180
self.Lat0 = Lat0 * pi / 180
self.m_0 = m_0
self.M0 = M0
self.a = a
self.e2 = e2
e4 = pow(e2, 2)


#Meridian distance Coefficients
self.A0 = 1 - (e2 / 4) - (3 * e4) / 64
self.A2 = (3.0 / 8.0) * (e2 + (e4 / 4.0))
self.A4 = (15.0 / 256.0) * e4


def MeridianDist(self, Lat):
return self.a * (self.A0 * Lat - self.A2 * sin(2 * Lat) + self.A4 * sin(4 * Lat))


#Coordinate Transform from grid to geographic in degree
def CoorTransform_GridToGeographic(self, Easting, Northing, accuracy = 9):
E0 = self.E0
N0 = self.N0
Lng0 = self.Lng0
Lat0 = self.Lat0
m_0 = self.m_0
M0 = self.M0
a = self.a
e2 = self.e2

#Convert from grid to geographic
#Calculate Lat_p by iteration of Meridian distance,
E_Delta = Easting - E0
N_delta = Northing - N0
Mp = (N_delta + M0) / m_0

Lat_min = -90 * pi / 180
Lat_max = 90 * pi / 180

accuracy = pow(10, -accuracy)

  #Newton 's method A0 = self.A0 A2 = self.A2 A4 = self.A4 Lat_p = (Lat_max + Lat_min) / 2 f = 1.1 while abs(f) > accuracy: f = Mp - self.MeridianDist(Lat_p) f_d1 = -a * (A0 - A2 * 2 * cos(2 * Lat_p) + A4 * 4 * cos(4 * Lat_p)) Lat_p = Lat_p - (f / f_d1)

t_p = tan(Lat_p)
v_p = a / pow((1.0 - e2 * pow(sin(Lat_p), 2)), (1 / 2))
p_p = (a * (1.0 - e2)) / pow((1 - e2 * pow(sin(Lat_p), 2)), (3 / 2))
W_p = v_p / p_p

Lng = Lng0 + (1 / cos(Lat_p)) * ((E_Delta / (m_0 * v_p)) - (1 / 6) * pow((E_Delta / (m_0 * v_p)), 3) * (W_p + 2 * pow(t_p, 2)))
Lat = Lat_p - (t_p / ((m_0 * p_p))) * (pow(E_Delta, 2) / ((2 * m_0 * v_p)))


return [Lng / pi * 180, Lat / pi * 180]


#Coordinate Transform from geographic in degree to grid
def CoorTransform_GeographicToGrid(self, Lng, Lat):
E0 = self.E0
N0 = self.N0
Lng0 = self.Lng0
Lat0 = self.Lat0
m_0 = self.m_0
M0 = self.M0
a = self.a
e2 = self.e2

#Convert Lat and Lng from degree to radian
Lng = Lng * pi / 180
Lat = Lat * pi / 180


#Convert from geographic to grid
Lng_Delta = Lng - Lng0
M = self.MeridianDist(Lat)

t_s = tan(Lat)
v_s = a / pow((1.0 - e2 * pow(sin(Lat), 2)), (1 / 2))
p_s = (a * (1.0 - e2)) / pow((1 - e2 * pow(sin(Lat), 2)), (3 / 2))
W_s = v_s / p_s

Easting = E0 + m_0 * v_s * (Lng_Delta * cos(Lat) + (1 / 6) * pow(Lng_Delta, 3) * pow(cos(Lat), 3) * pow(W_s - t_s, 2))
Northing = N0 + m_0 * ((M - M0) + v_s * (pow(Lng_Delta, 2) / 4) * sin(2 * Lat))


return [Easting, Northing]


#Coordinate Transform from HK1980 grid to WGS84 geographic in degree
def CoorTransform_Hk1980ToWgs84(self, Easting, Northing, Delimiter = ""):
LngLat_HK1980 = self.CoorTransform_GridToGeographic(Easting, Northing)

Lng_WGS84 = LngLat_HK1980[0] + (8.8 / 3600)
Lat_WGS84 = LngLat_HK1980[1] - (5.5 / 3600)


if Delimiter == "":
return [Lng_WGS84, Lat_WGS84]
else:
return str(Lng_WGS84) + Delimiter + str(Lat_WGS84)


#Coordinate Transform from WGS84 geographic in degree to HK1980 grid
def CoorTransform_Wgs84ToHK1980(self, Lng, Lat, Delimiter = ""):
Lng_HK1980 = Lng - (8.8 / 3600)
Lat_HK1980 = Lat + (5.5 / 3600)

EastNorth_HK1980 = self.CoorTransform_GeographicToGrid(Lng_HK1980, Lat_HK1980)


if Delimiter == "":
return EastNorth_HK1980
else:
return  str(EastNorth_HK1980(0)) & Delimiter & str(EastNorth_HK1980(1))