var
   FStream : TFileStream;
begin
   FStream:=TFileStream.Create('путь к передаваемому файлу', fmOpenRead);
   SendProcedure(FStream, UDPClient, StatusLabel, ProgressBar);
   FStream.Free;
end;

procedure SendProcedure(FStream: TFileStream; UDPClient: TIdUDPServer;);
var
   i,j,count: integer;
   buf : array[1..40000] of Char;
begin
   i := round(FStream.Size/40000);
   if (i*40000<FStream.Size) then i:=i+1;
   UDPClient.Send('localhost',9989,'count_buf:'+IntToStr(i)+'#');
   Application.ProcessMessages;
   for j:=1 to i do
   begin
     if i=j then
       count:=FStream.Read(buf,FStream.Size-((i-1)*40000))
     else
       count:=FStream.Read(buf,length(buf));

     UDPClient.SendBuffer('localhost', 9989, buf, count);
     while get_accept=false do Application.ProcessMessages;
     get_accept := false;
   end;
end;

procedure TMainForm.UDPServerUDPRead(Sender: TObject; AData: TStream;
   ABinding: TIdSocketHandle);
var
   str_buf : array[1..20] of Char;
begin
   // åñëè ïåðâûé ðàç, òî ñ÷èòûâàåì äàííûå îá êîëëè÷åñòâå ïàêåòîâ, êîòîðûå íóæíî áóäåò ïðèíÿòü
   // ñîçäàåì ïîòîê äëÿ ôàéëà
   if first_=true then
   begin
     AData.Read(str_buf,length(str_buf));
     if copy(str_buf,1,10)='count_buf:' then
     get_buffers:=StrToInt(copy(str_buf,11,pos('#',str_buf)-11));
     if SaveDialog.Execute then
     begin
       first_:=false;
       ServerStream:=TFileStream.Create(SaveDialog.FileName,fmCreate);
     end;
   end else
   begin
     get_buf_num:=get_buf_num+1;
     ServerStream.Position:=ServerStream.Size;
     ServerStream.CopyFrom(AData,AData.Size);
     UDPServer.Send('localhost',1152,'accept');
     if get_buffers=get_buf_num then
     begin
       ShowMessage('Âñå, ïðèíÿòî!');
       ServerStream.Free;
     end;
   end;
end;

procedure TMainForm.UDPClientUDPRead(Sender: TObject; AData: TStream;
   ABinding: TIdSocketHandle);
begin
   get_accept:=true;
end;