Hi makumbi,

Check the below sample code. Using the below article i have created the sample.

For saving mp4 video in database refer below article.

Display Binary Image from database in ASP.Net GridView control using C# and VB.Net

For sending email refer below article.

Attach File from MemoryStream to MailMessage object in ASP.Net using C# and VB.Net

HTML

<asp:Button Text="Send Email" runat="server" OnClick="OnSendEmail" />

Namespaces

C#

using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Net;
using System.Net.Mail;

VB.Net

Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient
Imports System.IO
Imports System.Net
Imports System.Net.Mail

Code

C#

protected void OnSendEmail(object sender, EventArgs e)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.CommandText = "SELECT Name, Data FROM tblFiles WHERE id = 4";
            cmd.Connection = con;
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                DataTable dt = new DataTable();
                sda.Fill(dt);
                byte[] bytes = (byte[])dt.Rows[0]["Data"];
                string name = dt.Rows[0]["Name"].ToString();

                MailMessage mm = new MailMessage("sender@gmail.com", "receiver@gmail.com");
                mm.Subject = "Test Video";
                mm.Body = "Video Attachment";
                mm.Attachments.Add(new Attachment(new MemoryStream(bytes), name));
                mm.IsBodyHtml = true;
                SmtpClient smtp = new SmtpClient();
                smtp.Host = "smtp.gmail.com";
                smtp.EnableSsl = true;
                NetworkCredential NetworkCred = new NetworkCredential();
                NetworkCred.UserName = "sender@gmail.com";
                NetworkCred.Password = "<password>";
                smtp.UseDefaultCredentials = true;
                smtp.Credentials = NetworkCred;
                smtp.Port = 587;
                smtp.Send(mm);
            }
        }
    }
}

VB.Net

Protected Sub OnSendEmail(ByVal sender As Object, ByVal e As EventArgs)
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand()
            cmd.CommandText = "SELECT Name, Data FROM tblFiles WHERE id = 4"
            cmd.Connection = con
            Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                Dim dt As DataTable = New DataTable()
                sda.Fill(dt)
                Dim bytes As Byte() = CType(dt.Rows(0)("Data"), Byte())
                Dim name As String = dt.Rows(0)("Name").ToString()

                Dim mm As MailMessage = New MailMessage("sender@gmail.com", "receiver@gmail.com")
                mm.Subject = "Test Video"
                mm.Body = "Video Attachment"
                mm.Attachments.Add(New Attachment(New MemoryStream(bytes), name))
                mm.IsBodyHtml = True
                Dim smtp As SmtpClient = New SmtpClient()
                smtp.Host = "smtp.gmail.com"
                smtp.EnableSsl = True
                Dim NetworkCred As NetworkCredential = New NetworkCredential()
                NetworkCred.UserName = "sender@gmail.com"
                NetworkCred.Password = "<password>"
                smtp.UseDefaultCredentials = True
                smtp.Credentials = NetworkCred
                smtp.Port = 587
                smtp.Send(mm)
            End Using
        End Using
    End Using
End Sub

Screenshot