Duplicate matching

From MythTV Official Wiki
Jump to: navigation, search

MythTV will, unless you tell it otherwise, try to record each episode of a show only once. To do so, MythTV compares showings in the listings that match recording rules to information about previously-recorded episodes (watched, unwatched, or deleted) of the program, checking for duplicates. The primary mechanism for duplicate matching is comparing program IDs, and there are four "fallback" methods.

Setup

Duplicate matching is configured by two settings in the recording rule's schedule options. The first setting has the following choices:

  • Don't match duplicates - Disable duplicate matching.
  • Match duplicates using subtitle & description - Enable duplicate matching using the program ID, falling back to the subtitle and the description.
  • Match duplicates using subtitle then description - Enable duplicate matching using the program ID, falling back to the subtitle then the description.
  • Match duplicates using subtitle - Enable duplicate matching using the program ID, falling back to the subtitle.
  • Match duplicates using description - Enable duplicate matching using the program ID, falling back to the description.

The second setting is available only if duplicate matching has been enabled by the first setting. It has the following choices:

  • Look for duplicates in current and previous recordings
  • Look for duplicates in current recordings only
  • Look for duplicates in previous recordings only

Program ID

The program ID is the definitive identifier of an episode. If the current episode described in the listings and a previously-recorded episode both have non-generic program IDs, then only the program ID will be compared to determine if the program is a duplicate. In this case the duplicate-matching fallback method specified by the recording rule will be ignored. If the program IDs are identical, MythTV will not record the new showing; if they differ, then the episode will not be considered a match, and MythTV will record it provided there are no other matching previously-recorded programs.

If the episode is a generic episode (for example, a Schedules Direct program ID of the format SH*0000), MythTV will record the episode, without regard to the program ID or duplicate-matching fallback method specified by the recording rule. A generic episode, by definition, means that an unknown episode is airing, so it is impossible for anyone--including MythTV--to know if it has been recorded before. Therefore, MythTV will always record generic episodes, just in case. If you want to exclude generic episodes, you must specify a filter (such as "Exclude unidentified episodes") for the duplicate matching scope in the recording rule.

If either the current episode described in the listings or the previously-recorded episode (or both) are missing a program ID, duplicate matching will be performed according to the duplicate-matching fallback method specified by the recording rule.

Fallback Methods

Subtitle

If the subtitle of the new episode and any previously-recorded episode match exactly, MythTV will not record the new showing.

Description

If the description of the new episode and any previously-recorded episode match exactly, MythTV will not record the new showing.

Subtitle and Description

If both the subtitle and description of the new episode and any previously-recorded episode match exactly, MythTV will not record the new showing.

Subtitle then Description

If the new episode has a subtitle and the subtitle of the new episode and any previously-recorded episode match exactly, MythTV will not record the new showing.

Otherwise, if the new episode does not have a subtitle and the description of the new episode and any previously-recorded episode match exactly, MythTV will not record the new showing.

FAQs

Q. I chose the duplicate check method 'Subtitle and Description,' and a set of episodes have the same subtitle and description, yet I still get duplicates.

A. All of those episodes also have a program ID, and when episodes have a program ID, the duplicate check fallback method is irrelevant. Only the program ID is used for comparison because the program ID is the definitive identifier of an episode.

Q. But all of the episodes have the same program ID.

A. True, but all three episodes have a SH*0000 program ID -- the Schedules Direct program ID used for generic episodes -- meaning which episode's airing is unknown. Rather than ignore this episode -- just because the listings provider wasn't given information on which episode was airing -- MythTV will record it.

The scheduler gives special treatment to any generic episodes (always recording them in case they're new). Schedules Direct/TMS data uses program IDs of the form SH (for show) followed by some digits identifying the program (title) and ending with 4 zeros (meaning unknown episode). If you want MythTV to skip recording generic episodes, you need to explicitly set the recording rule to "Exclude Generic Episodes."