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Do the DirecTivo's support sub channels?

Discussion in 'DIRECTV SD DVR/Receiver Discussion' started by rahlquist, Nov 4, 2008.

  1. rahlquist

    rahlquist Hall Of Fame

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    Hey fellas, got a interesting idea. Do the DirecTivos support Sub channels in the same manner as the HRx? I was just mulling over it today and was wondering if the grey/black/blank recording issues may be bad guide data that tricks the HR into grabbing a sub channel that doesnt exist?

    If the DirecTivo doesnt support the subchannel architecture perhaps thats why it was never an issue on them?
     
  2. say-what

    say-what Active Member

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    I don't think the issue has anything to do with subchannels as people report the problem for recordings on Sat channels without -1 counterparts.
     
  3. rahlquist

    rahlquist Hall Of Fame

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    Exactly my point. Through corrupt guide data possibly via;
    • corruption in db
    • fs corruption
    • random glitch
    They get a recording that is tuning to something 'not there'. Thereby creating the blank/black/grey recording.

    It is just a thought. I cant think of any way to prove/disprove it as an end user. Just hope D* can.
     
  4. Doug Brott

    Doug Brott Lifetime Achiever DBSTalk Club

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    Internally, every single channel has a unique identifier .. The "-1" channels are just a way to make it more understandable for humans (sorting, etc.).
     
  5. rahlquist

    rahlquist Hall Of Fame

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    Ok so lets assume for the sake of argument that that identifier (which I believe would be stored in the guide DB) got corrupted for a short period of time. If the dvr grabbed that identifier and tried to tune to and record a program from a non existent channel would it possibly be a blank recording?

    Think in VCR terms for a moment.

    A VCR never had a guide. We scheduled it to to tune to channel say 64 at 10am and record till 11am.

    What if the 64 got corrupted or nulled out and it recorded channel 0?

    Extend that out in DB terms. The db likley has a column for channel description( the human readable part ) and the uid, in the case of a subchan is that subchan indicated by any other field in the db? Or only the uid field? How is that structurally different than the DirecTivo since it never seemed to have this blank recording issue. I just think this is possibly usable by the devs as a way to cross check the problem.
     
  6. Doug Brott

    Doug Brott Lifetime Achiever DBSTalk Club

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    You've got to remember that Guide Data is being transmitted continuously so the receiver picks up on this data. Any corruption will likely be corrected even after a program may have been started. On top of that, since there is no guarantee that they Guide Data is transmitted correctly just by sending it, there has to be some sort of checksum just to make sure that what was sent is what was received. Otherwise DIRECTV would blindly be dropping the data from the sky hoping that every receiver out there (millions) got the exact right answer. So I do not think that corrupt transmission is the issue.

    What is almost certainly the case with any blank recording is that the receiver someone is "on" but cannot see the channel being recorded at the recording time. This could be due to any number of technical or hardware issue (including temporary issues). We've seen here folks with bad LNBs that sometimes work and sometimes don't work .. That's a very plausible case for how a blank recording may get created. Replacing the LNB solved this problem for a lot of folks, but is not the sole source of the problem.

    My point is, that the Guide Data Transmission is not the right place to be looking for this problem. Besides, the blank recordings issue is greatly improved over the past few months and I think this is in large part due to the proactive calls that DIRECTV has been making when satellite signals are not operating in the correct range.
     
  7. rahlquist

    rahlquist Hall Of Fame

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    Thank you Doug. It was just an idea that came to mind today after reading various threads. Since we had a control (the Tivo units) that hadn't displayed this particular error at least in the numbers we seem to see with the HR it just came to mind.

    With regard to the checksum I am with you I cant imagine they would not checksum their data, however, would the checksum be checked after the data has had its final commit to its semi permanent space in the DB or as its being decompressed to store in the DB (assuming guide data is compressed in the stream). Since it is indeed overwritten as updated this could explain further why it could pass its checksum but if a bit was corrupt on the drive, would fail when called upon to provide the input data to start a recording. A lot of ifs but we are talking about a problem that effects a very small percentage.

    As I pointed out in ( http://www.dbstalk.com/showpost.php?p=1870514&postcount=21 ) its possible to have a DVR have a bad drive and still function for the most part and the scary part is that Phillip DirecTivo I mention in that post would probably have passed a 'refurbish' inspection unless they ran an exhaustive scan of the drive for surface errors like I did before I dumped it. In the case of that Tivo DVR it stored a movie over the bad area and never skipped a beat, just couldn't read it.

    Anyhow just mainly wanted to put this out there in case it may be of use to the devs in any way. Thank you for the insight. You can lock this one if you want.
     

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