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Priority One HR20-100 Bug: Recordings start late

Discussion in 'DIRECTV HD DVR/Receiver Discussion' started by TigerDriver, Oct 26, 2007.

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  1. TigerDriver

    TigerDriver Electronics Engineer

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    Jul 27, 2007
    I've been working a bug on a thread named "HR20 Clock" where folks are complaining that recordings on their HR20-100s are chopping of the first half-minute or so of the recording.

    I don't know whether this bug is universal, or whether users just haven't noticed it. I got involved not because I had noticed this delay in my own recordings, but because it sounded interesting (and important). Once I learned of the problem I realized that I had it. My hunch is that if this problem is not universal, it's widespread.

    After lots of thrashing and wool-gathering among the contributors, member blarnson characterized the bug:


    Here's a quick way to confirm this bug:

    A couple of minutes before the hour or half hour:
    1. Select Guide.
    2. Keep an eye on the clock under D* logo. (It has only one-minute resolution).
    3. When the clock turns over to the time of the next program, note that PIG simultaneously changes to that program.
    4. Guide does not update (shift left) immediately.
    5. After X number of seconds pass, the Guide updates.
    6. If you've scheduled the upcoming show to record, the record light comes on when as/after the Guide updates.
    7. If you note the content of the audio/video in the PIG at the moment the Guide updates, upon playback you'll find that that's when the recording begins.

    So, the HR20 behaves as if:

    (1) Channel change is triggered by real-time clock.
    (2) Recorder startup is triggered by Guide update.
    (3) Guide update occurs X seconds later than real-time clock.

    I did not test any corner-cases; for example, what happens on manually scheduled recordings that are not close in time to a Guide update; or what happens when shows record back-to-back on the same channel or different channels.

    This behavior is invariant and reproducible. On my HR20-100, X is about 28 seconds, but higher values have been reported. IMHO, this ought to be treated as a priority-one bug, as it interferes with the fundamental behavior for which users acquire the DVR. (If the engineering group at D* has a regression testing harness, this ought to go on it.)
     
  2. Sirshagg

    Sirshagg Hall Of Fame

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    Dec 29, 2006
    it's not just on the 100.
     
  3. jkast

    jkast Cool Member

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    I have noticed my recorded shows are starting a little late on both HR20-100s I have. I agree this should be high priority. On some shows you miss something key in the first few seconds (e.g. Monk) on others you just miss the boilerplate intro... But it is really distracting,,
     
  4. weaver6

    weaver6 Icon

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    My -100 has always started late. My observations track blarnson's.
     
  5. Ken S

    Ken S RIP

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    It's most definitely an HR20-700 bug as well.
     
  6. Sirshagg

    Sirshagg Hall Of Fame

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    Both of my 700's do this too. Each one is devoted to 2 of the four major networks so I record alot of things back to back. I've now gotten used to watching them in the order the network shows them so that i can catch the first minute of the second show on the end of the first, etc. Unfortunately this doesn't help for the first show or when i don't record the entire evening on that channel.

    I can't set padding becasue both units also record many shows on other channels too and this would create conflicts.
     
  7. mikeny

    mikeny Hall Of Fame

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    I agree with you. My HR20-700 has always started recording certain shows into the first minute. "The Office" is one that comes to mind. I have adjusted that SL so that it starts earlier.
     
  8. Steve

    Steve Well-Known Member

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    My four HR20's are always within 2-3 seconds of the atomic clock at "time.gov", so I don't believe the HR20 clock is the issue.

    I have a theory, however, about why some recordings start late. 3-4 seconds of the loss of the beginning of a show may be due to the clock. Another 3-4 seconds of it is the time it takes to change the channel. And another 3-4 seconds may be due to the time it takes to change resolutions (though I'm not sure this part is true). And don't forget that the network clocks may be off a few seconds. When three or four of these things occur before one recording, a show will start 10 or more seconds late. I say this because on consecutive recordings on the same channel, shows seem to start right on the dot.

    So I wouldn't call this a "CLOCK BUG" per se, I'd call it a performance issue. And no, you can't just start each recording 15 seconds early, because it depends on whether or not there may be free tuners at that time. :)

    Of course, if we get the Wish List request to "Always pad start/stop time by one minute when possible", that will help.

    What will definitely help, IMO, is if D* can improve channel/resolution change performance, but this may not be possible. It could just be the nature of the beast that these things can't happen faster.

    /steve
     
  9. SoGaShelby

    SoGaShelby New Member

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    Sep 22, 2007
    My HR20-700 is 53 seconds behind the clock at time.gov and has been the past 2 days I have been tracking. My shows always start recording late, even when the shows are back to back on the same channel so there should be no channel changing time or resolution changing time.

    My Samsung SIR-TS360 sitting next to my HR20 is 3 seconds behind. When displaying the same channel on both units in PIP the pictures are almost in sync.
     
  10. Steve

    Steve Well-Known Member

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    Very odd. I just now spot-checked two of my four HR20's. One was 2 seconds off from time.gov, the other 3 seconds. Weird you are so far off, because I'm pretty sure the HR20 clocks are updated at least once a day during the routine sat data downloads.

    I'm comparing time.gov to the INFO banner clock during live TV, which changes in real-time, even while the banner is frozen on screen. /steve

    EDIT: The test above was using EASTERN TIME ZONE at time.gov. I tried it again using ATLANTIC TIME ZONE, and the HR20 that was 3 seconds behind was now actually 1 second ahead of TIME.GOV! Now I wonder how reliable testing with Time.Gov is? Either way, the times still match pretty closely, however.
     
  11. TigerDriver

    TigerDriver Electronics Engineer

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    Jul 27, 2007
    1. This assumes that the satellite clock always lags (rather than leads) atomic time. I don't know whether this is true, but if not, on average it should be a push. FTR, my HR20-100 clock is -3 seconds compared to time.gov.

    2. I also performed the test so that a channel change would be necessary. I had no way to time it of course, but subjectively, based upon watching the PIG, it seemed to occur in less than a second. This would depend, I suspect, on whether the channel change requires another satellite and/or transponder.

    3. Unless I misunderstand the architecture, resolution shouldn't be an issue here: the DVR just sucks down and records a stream.

    4. You're right--it's not a clock bug, which is is why I started a new thread with a new name.

    The bug appears to be that the recording is synchronized with the Guide update, instead of with the scheduled "real" time. If D* engineering has a good reason for this way (I'm all ears), then the bug becomes "Guide updates occur several seconds behind real-time clock." Common sense, however, says that updating the guide ought to be the lowest priority event in the chain.

    5. There's no evidence that this performance is inevitable; as other have noted, it doesn't occur on the HR10.

    As I said earlier, I'm all ears. But based upon my own painful experiences, this has all the earmarks of an ugly, high-visibility bug caused by poor engineering hygiene. This problem was probably hacked in during prototyping--the "let's just get something working" phase--and never got expunged because nobody noticed its pathological consequences. (And what does all this tell us about D* QA processes?)
     
  12. w6fxj

    w6fxj DBSTalk Club Member

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    Aug 10, 2005
    Joe - My observations is that the displayed time in the guide does NOT update on time after the initial display. But the displayed time is "correct" when one first displays the guide. One can check this effect by repeatedly going in and out of the guide while checking the displayed time. Then observing when the display updates while the guide stays up.
     
  13. TigerDriver

    TigerDriver Electronics Engineer

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    I suspected as much.

    I'd change the name in the thread title, to "HR20-x00" but I don't see a way to edit the thread title.
     
  14. TigerDriver

    TigerDriver Electronics Engineer

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    I'm not sure I follow you, but I'm going to put my guide up now, note the difference between it and atomic time. I'll come back in an hour and check the guide time again. Are you saying that that the difference will change?
     
  15. SoGaShelby

    SoGaShelby New Member

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    Sep 22, 2007
    About 12:50 Eastern I turned power off on both HR20-700 and SIR-TS360 for about a minute. When both units came back up they were both about 4 seconds behind time.com (Eastern). While watching show I kept pressing Info to compare. It seemed to be consistently about 4 seconds behind when all of a sudden it was about 12 seconds ahead. After watching for a while it seems to track 4 seconds behind except on the 5 min intervals, then the clock is ahead about 8 seconds. The next minute will be back to 4 seconds behind.

    I set two shows to record at 1:30 on different channels than my tuners were set to record. While displaying the guide the guide time actually went to 1:30 ahead of time.com but the guide did not change until the channels changed about 5 seconds after time.com change. The light came on to record about a second after channel change.

    Not sure what this means but appears displayed time in guide and info does not control recording or channel change. Must be another clock or timer.

    EDIT: Watching the clock using only INFO it is always behind except for the 5 min. intervals. However, when I check guide for time, if I am in the second half of the minute it shows the next minute, 30 seconds ahead of time. Pressing info after that shows the later time. Set another show to record and it seems to start 4 seconds behind time.com, even when guide has shown start time for 25 seconds.
     
  16. Steve

    Steve Well-Known Member

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    So it seems like the GUIDE "rounds up" in 30 second intervals once real time hits 00: and :30. Better to use INFO. The 3-4 second INFO banner differential from time.gov must be simply related to satellite lag.

    D* should compensate for sat lag when they do the daily updates, don't you think? Add that lag to channel change lag and whatever error exists in the broadcaster's clock and you can easily be off 10-15 seconds on each recording's start, assuming nothing else goes wrong. /steve
     
  17. DarkAudit

    DarkAudit Godfather

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    Sep 10, 2007
    Does the HR21 show the same error?
     
  18. fudpucker

    fudpucker Godfather

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    NW Iowa
    I've been beating my head on the wall on this problem as long as I've had my HR20s (100s) - this happens on both of them, and I've watched it in progress. The problem occurs exactly the same if I'm already on the channel to record - I've observed that by having the TV on the channel, watching as I waited for it to start recording the program, watching the clock change to 8:00 and the program start up, then about 20 - 30 seconds later seeing the record light come on (and confirming that the recording started where the record light came on - 20 something seconds late.)

    This forces me to do things like start recordings 1 minute early, but that then interferes when I have numerous shows scheduled to record.

    This really, really needs to be fixed - this is a very fundamental problem to the whole basis for having a DVR.
     
  19. Drewcipher

    Drewcipher Cool Member

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    Jul 7, 2007
    I just checked one of my HR20s and it was about 20 seconds ahead of time.gov, but I still have the problem of missing the start of some shows. Is it possible that the networks are playing with the start times in an attempt to screw DVR users?
     
  20. Tenor72

    Tenor72 New Member

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    May 12, 2007
    Fix this clock issue Directv. If someone from Directv really reads this forum please correct the clock issue on the HR20. It is very frustrating playing a show back that starts late.
     
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