2004-02-29 14:21:22 +01:00
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VPS (Video Programming Service)
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===============================
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Beginning with version 1.3.5 VDR supports the VPS method
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of identifying programmes to record, and making sure they
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are recorded in full length, even if they run longer than
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initially specified or are shifted in time.
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Of course, the main prerequisite for this to work is that
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the broadcasters actually provide the necessary data. In
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particular these are
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- EPG data (well, obviously)
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- the data for each event must contain the "Programme Identification Label"
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descriptor, which contains the VPS timestamp for this programme
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- the event data must provide and maintain the "Running Status" flag,
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which indicates whether this programme is currently running or not.
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Currently only the German "<22>ffentlich Rechtliche" tv stations provide
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the necessary VPS data, so this will work only for stations like "Das Erste",
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"ZDF" and the like.
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Following is a step by step description of what happens for a VPS controlled
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timer recording. First let's take a look at what the VDR user needs to do.
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VPS as seen by the VDR user:
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----------------------------
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When the VDR user sets up a timer that shall be under VPS control, there
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are only two things that need to be done:
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1. Set the "Start" time to the actual VPS time as published in tv magazines.
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Typically the VPS time is the same as the printed start time, unless
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expliciltly specified otherwise. For instance, a tv magazine might print
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20:15 Wetten, dass...?
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(VPS = 20:14)
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In this case the timer would need to be set to 20:14.
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2. Set the "VPS" flag in the timer definition to "yes" in order to tell VDR
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that this timer is to be handled under VPS control. This is no different
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to old analog video recorders, where each timer has also had a separate
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VPS flag.
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If the user sets up a timer from the "Schedule" menu, things are even simpler.
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If the setup option "Recording/Use VPS" is set to "yes", any timer that is
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programmed from an event that has VPS information will automatically be set
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up as a VPS timer.
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IMPORTANT: In order for a recording to work under VPS control it is of
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========== paramount importance that the start time is set to the actual
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VPS time of that event, NOT some time a few minutes before the
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event starts! If a timer is set to use VPS, and the time doesn't
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match any event's VPS time, nothing will be recorded!
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VPS as seen by VDR:
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-------------------
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The following things happen when VDR processes timers:
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- VDR regularly scans the EPG data and assigns events to the timers (see
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cTimers::SetEvents() in VDR/timers.c).
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This can be seen in the log file as
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timer 1 (15 1830-1900 'Neues') set to event 28.02.2004 18:30-18:59 (VPS: 28.02 18:30) 'neues'
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- When a VPS timer is asked whether it matches (i.e. whether a recording shall
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be started), it checks whether it has an event assigned to it, and whether
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that event has a running status of "starts in a few seconds" or "running"
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(see cTimer::Matches(time_t t, bool Directly) in VDR/timers.c). This allows
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the recording process to catch the entire programme, even if it runs longer
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than initially advertised. It also works if it runs shorter or gets shifted.
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- When a VPS timer event is coming up (i.e. there are only a few minutes until
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it starts, according to the related event data's start time - which may be
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different than the VPS time!), VDR tunes a free DVB device to that transponder
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(unless there is already a device tuned to that one) in order to make sure
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that the event data (especially the "Running Status") will be up to date and
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a change in the "Running status" flag will be seen immediately. This may
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lead to the primary device being switched to a different channel if there
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is no other free DVB device available. See the main program loop in VDR/vdr.c,
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"Make sure VPS timers "see" their channel early enough:".
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Problems:
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---------
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- In order for a VPS controlled timer to function properly, it needs to "see"
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any changes in the running status of its event. This means that one of the
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DVB devices needs to be tuned to the proper transponder some time before
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the actual start time of the event. However, this may result in an other
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timer (with lower priority) to be stopped, because it occupies the DVB device
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and has it tuned to a different transponder.
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See "// Make sure VPS timers "see" their channel early enough:" in VDR/vdr.c.
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TODO:
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Something needs to be done to prevent two timers from repeatedly switching
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the device between channels in such a situation.
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- If, for some reason, the driver doesn't deliver any more section data, a
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VPS controlled timer will never see that the programme has started (or ended).
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TODO:
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Therefore some mechanism needs to be implemented that makes absolutely sure
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we continuously receive at least the event data for the present event.
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Caveats:
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--------
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Apparently VPS in digital broadcasting is still in an early state. Only few
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tv stations actually support it, and other tv stations don't even handle the
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"Running Status" correctly (which, by itself, would already be helpful, even
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without VPS).
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Here's a list of things that are apparently done wrong by the individual
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stations:
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- The German "<22>ffentlich Rechtliche" tv stations, although supporting VPS,
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don't switch the "Running Status" of an upcoming broadcast to "starts in
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a few seconds", but rather go directly from "unknown" or "not running" to
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"running". This may result in a recording that misses the first few seconds
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of the programme.
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- The RTL group handles EPG events in a rather random way. They change event
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IDs randomly, and switch the "Running Status" flag at times that are only
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losely related to the actual events. For instance, if the "RTL aktuell"
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programme starts at 18:45, they switch that event to "running" at about
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18:43. Or, even worse, if "Wer wird Million<6F>r?" runs until 21:15, they
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switch the _next_ programme to running (which implicitly set "Wer wird
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Million<6F>r?" to "not running) at around 21:11 - so anybody using that
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information to control recording would not see the end of that programme.
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... more following as it comes up...
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2004-03-03 19:20:20 +01:00
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Contact:
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--------
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ARD Digital: http://www.ard-digital.de/home/index.php?id=16&languageid=1
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ZDF vision: http://www.zdf.de/ZDFde/inhalt/1/0,1872,1021601,00.html (select "zdfvision")
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