Difference between revisions of "Mythbackend"

Revision as of 20:24, 13 December 2009

The backend process (mythbackend) is the portion of the system that handles the Video capture cards as well as Scheduling Recordings on those cards, Commercial Flagging, and transcoding. The backend process interacts with the Database primarily.

As with the MythFrontend, there can be multiple backends. One backend process is designated as the master backend. This is usually the first backend installed on a system. This backend is responsible for coordinating the activities of the other backends known as slaves. This is especially true for scheduling as the master backend will determine the best distribution of programs across all available tuners. Each backend can have any number of tuners, including zero. As of 0.16, Commercial Flagging can be distributed across different backends, thereby spreading the load of that process.

There is no requirement for direct user interaction with the backend. The backend can use local HardWare/File Storage or have it mounted from another system. If remotely mounted, network performance should be considered as there will be considerable traffic on the network as recordings are stored and retreived by the backend process.

Command Line Options

Valid options are:

-h or --help                   List valid command line parameters
-l or --logfile filename       Writes STDERR and STDOUT messages to filename
-p or --pidfile filename       Write PID of mythbackend to filename
-d or --daemon                 Runs mythbackend as a daemon
-v or --verbose debug-level    Use '-v help' for level info
--printexpire                  List of auto-expire programs
--printsched                   Upcoming scheduled programs
--testsched                    Test run scheduler (ignore existing schedule)
--resched                      Force the scheduler to update
--nosched                      Do not perform any scheduling
--noupnp                       Do not enable the UPNP server
--nojobqueue                   Do not start the JobQueue
--nohousekeeper                Do not start the Housekeeper
--noautoexpire                 Do not start the AutoExpire thread
--version                      Version information

Communications Protocol

The backend and frontend communicate using their own Myth Protocol. The developer of Win Myth, a windows frontend to MythTV for playing recordings on Windows, has documented his workings on the procotol here. Work on defining the Myth Protocol is also be performed on this Wiki.

Troubleshooting

To control what debug information is logged to the log file the following switches may be used. These can be viewed by entering 'mythbackend -v help'

Verbose debug levels. Accepts any combination (separated by comma) of:

 all           - ALL available debug output
 most          - Most debug (nodatabase,notimestamp)
 important     - Errors or other very important messages
 general       - General info
 record        - Recording related messages
 playback      - Playback related messages
 channel       - Channel related messages
 osd           - On-Screen Display related messages
 file          - File and AutoExpire related messages
 schedule      - Scheduling related messages
 network       - Network protocol related messages
 commflag      - Commercial Flagging related messages
 audio         - Audio related messages
 libav         - Enables libav debugging
 jobqueue      - JobQueue related messages
 siparser      - Siparser related messages
 eit           - EIT related messages
 vbi           - VBI related messages
 database      - Display all SQL commands executed
 dsmcc         - DSMCC carousel related messages
 mheg          - MHEG debugging messages
 upnp          - upnp debugging messages
 socket        - socket debugging messages
 xmltv         - xmltv output and related messages
 dvbcam        - DVB CAM debugging messages
 media         - Media Manager debugging messages
 idle          - System idle messages
 timestamp     - Conditional data driven messages
 none          - NO debug output

The default for this program appears to be: '-v important,general'

Most options are additive except for none, all, and important. These three are semi-explicit and take precedence over any prior options given. You can however use something like '-v none,jobqueue' to get only JobQueue related messages and override the default verbosity level.

The additive options may also be subtracted from 'all' by prefixing them with 'no', so you may use '-v all,nodatabase' to view all but database debug messages.

Some debug levels may not apply to this program.

Need to add backend-specific troubleshooting help here, or at least link to Troubleshooting

Interpreting --printsched Output

The --printsched command line option prints out upcoming scheduled recordings. For example:

Title - Subtitle                Ch Station Day Start  End   S C I  T N   Pri
Ask This Old House - "Installi 21_2 WLIWDT2 13 16:30-17:00   1 0 0 A R 2/    0
Family Guy - "Mother Tucker"     11 WPIX    13 19:00-19:30   1 0 0 A R 2/    0

Title, subtitle, channel, station, day, start and end are rather straight forward. The meaning s of the single characters are:

• S - Source ID
• C - Card ID
• I - Input ID
• T - Recording Type Character
• N - Recording Status Character

The meanings of the Recording Type Character are:

• S - Single record
• T - Timeslot
• W - Weekslot
• C - Channel
• A - All
• F - Find one
• d - Find one daily
• w - Find weekly
• O - Override or Don't record

The meanings of the recording status character is:

• A - Aborted
• R - Recorded / Current recording
• X - Don't record
• P - Previous recording
• E - Earlier showing
• T - Too many recordings
• c - Cancelled
• M - Missed
• C - Conflict
• L - Later showing
• r - Repeat
• x - Inactive
• K - Low disk space
• B - Tuner busy
• f - Failed
• N - Not listed
• V - Never record
• F - Offline
• O - Other showing
• (a number) - the card ID on which the show is currently recording