<episode-num system="common">S04E22</episode-num>
This seems to be something new. And it looks like it should be straight forward. "S04E22" means season 4, episode 22, I suppose.
This is the format created by the author of zap2xml in April this year. It is a completely logical numbering system, but it is not part of the XMLTV standard. I actually asked the author of EPG Collector if he would produce that format in the output of EPGC, and he was willing, but a little concerned that it did not in any way meet the standard.
<episode-num system="dd_progid">EP00016916.0073</episode-num>
This is still something I do not understand (some proprietary format).
This is the format created by Zap2It, or the owners, Tribune Media Services. It is also not part of the XMLTV standard. The part before the "." is a Program ID number, which I think is specific to Zap2It, and not consistent with thetvdb.com, imdb.com, or any other internet repository. The number portion of the Program ID is used to link recordings in a series, and for metadata lookup. The prefix, in this case "EP", indicates that this is an episodic program, and so there are seasons and episodes. There are other prefixes with other meanings. I believe that you have to be using Zap2It aware products to make sense of it. The part after the "." is the absolute episode number. That is, if a program had 10 episodes per season, the third episode in the third season would be the 23rd episode, and so would be numbered ".0023". This system requires that the number of episodes in each season is known in order to convert to a Season number and Episode number format.
Basically, don't bother ever trying to interpret that format. Even if you understand what it is doing, additional episodes like a "The Making Of program" or Christmas specials may or may not be correctly included in the episode count, so you can still get the Season and Episode numbers wrong.
<episode-num system="xmltv_ns">2 . 9 . 0/1</episode-num>
This is also straight forward, and I meant to add its support a while ago.
This is the only sensible numbering format in the XMLTV standard. Don't forget that it starts the count for Season and Episodes from zero though. i.e. The program above is Episode 10 from Season 3, and it is a 1 Part episode.
So look for some improvement in this area in the next few builds of MC20.
Indeed I am.
Thank you Yaobing.