Detecting and fixing Channels in Media Center 7

One of the to-do's I have on my Streaming Tuner is to detect the channel call signs on the client computer for the encoded analog channels that are now digital. The second to-do was to get the channels to match up with guide information.

I managed to get the channels detected by scrubbing the transport stream (TS) created by the mpeg-2 encoder in the graph. I needed to edit the PAT and PMT - to change the program number of the stream and add additional streams (MCE does not like duplicate program numbers - I discovered after many hours of head banging). Then I needed to inject PSIP packets (namely MGT, CVCT and EIT) which would enable MCE to detect the callsigns of the channels. Needless to say I now consider myself to be somewhat of an expert in PSIP having thoroughly read the specifications and the book PSIP: Program And System Information Protocol: Naming, Numbering, and Navigation for Digital Television from cover to cover.

To get the callsigns turned out to be a much more complex the MCE 6 SDK has a few annoying features - one of which is the inability to provide channel names in cases where there are multiple sub-channels on the same channel number. As can be seen in the first image. Using the GetCallSigns method returns a serviceID and a callsign then by using the GetServiceIds method, which returns serviceID and channel number, one should theoretically be able to map the callsign to the channel number by using the serviceID and a common variable.

Figure 1 Channel 5.x on server

However as I mentioned earlier this does not work because for channel 5 only the serviceID of WPTVDT2 is returned with a channel number of 5.

I then shifted my focus to using XMLTV but that now requires a subscription for US guide data and the used would have to configure XMLTV as well as Media Center which would leave way to much space for mistakes. In addition to that I had not found a way for the client to match callsign to guide data yet.

Figure 2 Channel detection on client

Finally I decided to revisit getting the information from the media center database. I imported mcepg.dll into a project and voila I saw almost everything I needed. After a few hours I was able to pull the scanned analog lineup out of the database into an XML file.

 
 

Figure 3 Part of channel configuration file

Now all that was needed was to get the client side to edit the guide listing programmatically. I knew this was possible because you can import MXF formatted XML into media center. I had a look at that but it seemed more effort than it was worth. I decided to use the mcepg.dll again to edit the guide on the client side. This was also a pretty simple task except for the fact that I was getting exceptions every time I called the
Microsoft.MediaCenter.Guide.MergedChannel.AddChannelListings(Channel) method. I wrapped this in try catch and it worked fine - but I don't like hiding problems in code so I spent about a day finding out what was causing the exception (luckily I learnt to program in the days when asm was needed) - I narrowed it down to a inactive DeviceGroup. I tried a number of workarounds and finally managed to find one that would allow me to make my changes without corrupting the database of causing exceptions.

Figure 4 Client guide after channel scanning

Not only have I managed to programmatically remap scanned channels to a legitimate guide channel I have also managed to change a channel.subchannel into a channel number without any sub channels. The last image shows the guide after I did the first 2 channels 1.2 and 1.3. I know no one uses channel 1.x for anything so I just sent the channel on PSIP and major=1 and subchannel=analog channel number.

Figure 5 First 2 channels fixed

Next week I will finish up the installer and clean up a couple of issues so that I can make an alpha build and send it off to everyone that requested it. I think I might just also create a GUI for people to change their Guide information as well. I know I hate going through the "edit listing" menu and searching for a matching listing to map my clearQAM to my cablecard channels.