[mythtv-users] Recordings start & end 10 seconds too soon, on all channels

[steve]

> On Mar 22, 2016, at 7:25 AM, Michael T. Dean <mtdean at thirdcontact.com> wrote:
> 
> On 03/22/2016 12:45 AM, steve wrote:
>> On Mar 21, 2016, at 10:33 PM, Michael T. Dean wrote:
>>> (fixed top posting)
>>> 
>>> On 03/21/2016 07:31 PM, steve wrote:
>>>> On Mar 21, 2016, at 7:19 PM, Bill Meek wrote:
>>>> 
>>>>> On 03/21/2016 04:07 PM, steve wrote:
>>>>>> My system time is correct to the exact second, so I assume an os level ntp is enabled and working fine.
>>>>>> Ubuntu 14.04 LT
>>>>>> Myth 27.6
>>> What makes you think recordings start and end 10 seconds too soon on all channels?
>>> 
>>>>> Have you changed anything like: Time to record before start of show (secs)
>>>>> in the frontend Setup->Video->General about 4 pages in?
>>>> Thanks, I thought for certain you nailed it...  but unfortunately, it wasn't that one
>>>>   Time to record before start of show (secs): 0
>>>> Time to record before past end of show (secs): 1 <-- Did I change this to 1?    I'll set it to 0 now.
>>>> 
>>>> Any other ideas?
>>> Are you sure your broadcaster/rebroadcaster is airing shows "to the exact second"?  Especially if it's a rebroadcaster and/or if your video is going through some intermediate tuner/decoder/..., there may be some delay in the actual delivery of the video, which could appear as if MythTV were starting and ending shows too early.
>>> 
>>> Or are you saying that the mythbackend logs show mythbackend starting a recording at 10 seconds before the start time (where, there should be a slightly early start--though I'm thinking it's more like 2 seconds, IIRC) and ending the recording 10 seconds before the end time, based on the time stamps in the log?
>>> 
>>> In other words, you really need to show us some log files to get anything other than guesses (albeit, educated guesses). https://www.mythtv.org/wiki/Posting_Logs
>> Sorry, you were right. Just checked the logs and it shows Myth is performing accurately, ie a show set to record at 23:00:00 indeed starts its recording at exactly 23:00:00.
>> 
>> Yet my problem persists in that shows are still starting about 8-10s early and ending 8-10s early.
> 
> So now is the time you do set those settings Bill mentioned. :)
> 
>> This is with comcast cable cards and an HD Homerun Prime.
>> 
>> And since it affects recordings on all channels equally, I guess you could think its the broadcaster...
> 
> Right.  Very common with rebroadcasts (i.e. cable/satellite service, as opposed to the original broadcasts received OTA), especially now with "intermediate processing equipment" (decoding boxes, like cable box or HDHR Prime with CableCARD).
> 
>>  but what I don't understand is that I am coming from Windows Media Center with the same tuners, and I did not notice this problem there.
> 
> WMC may have started early and ended late--assuming you were using the HDHR Prime and the same Comcast service with it.  Especially if you don't record much (meaning you don't get tons of back-to-back recordings on the same input), you likely wouldn't have noticed.
> 
>> If I can't get to the root of it, then is there a way I can to just compensate for it in mythbackend? Tell mythbackend to start and end all recordings 10 seconds late to compensate?
> 
> You can set "Time to record before start of show (secs)" and "Time to record past end of show (secs)" to some value (generally greater than the amount of offset you're seeing--like 20s or so), but note that the over-record is not guaranteed.  If you have back-to-back recordings on the same input, MythTV will switch at the exact scheduled time and you won't get any over-record (extra time on end of the first show and extra time at beginning of the second show).  Therefore, if you set those settings, you'll generally only get the 20s extra time at the beginning of prime time and the end of prime time--i.e. you'll record from 7:59:40 until 8:30:00 and from 8:30:00 to 9:00:00 and from 9:00:00 to 10:00:00 and from 10:00:00 to 11:00:20 or whatever. Therefore, these settings will not solve the problem--they'll only ameliorate it on some "stand alone" shows.
> 
> To guarantee an over-record (to include it in MythTV's schedule), you must set "Start Early" and "End Late" (which are both in minutes) on the recording rule.  Note, however, if you set "End Late" on a show that ends at 8:30, you're saying that recording can not be ended until 8:31, so if you have another show that starts at 8:30 (or, with "Start Early" at 8:29), you will get a conflict--meaning MythTV cannot record the lower-priority show unless you have another input available.
> 
> So, what's the answer when you need to Start Early and End Late and those settings in the recording rule cause conflicts which prevent your recording all the shows you want to record?  You have 2 options:  a) remove the Start Early and End late from the recording rules and live without those seconds you lose or b) get more inputs (i.e. more HDHR Primes and CableCARDs) and live without the money for the extra equipment (including the cable company's monthly extra equipment charge).
> 
> MythTV doesn't have a means to offset everything by any small amount because we trust the listings data--if it says the show starts at 8:00, we assume the show starts at 8:00.  At least in the past, it was far more common for different shows (even on the same channel) as well as for different channels to be offset by different amounts.  A constant 10s offset on everything implies a systemic issue (specifically the time it takes your HDHR Prime to get the decrypted video from your CableCARD or some systemic delay introduced by Comcast).
> 
> Other than that, you'd have to come up with some dirty hacks to get around it.  For example, modifying your listings grabber such that you can pre-process the listings before insertion into the database and offset all the start/end times by 10s (so that your listings show something starting at 7:59:50).  Or, even dirtier, running your system with its clock offset by 10s.  Of the 2, modifying your listings is probably the better approach (because, remember, MythTV is programmed to trust the listings)--though it does look ugly in your guide/recorded programs.  (And doing so before they're put in the database is the proper way to modify your listings--so you don't mess up MythTV by "pulling the rug"--or the schedule--out from under it.)

Thank you very much, I appreciate your detailed reply. 

I have 2 HDHomerun x 3 tuners = 6 tuners 

I suspect you are right, that from Windows Media Center, running on these same 6 tuners, same comcast, that I had a global settings set that said to always record an extra minute or 2, that I forgot about.

I think I understand what you are saying with the 2 methods, but I am unclear the ramifications of each. 

I like that the first method can specify in seconds not minutes.

If I go with the first method, "Time to record before start of show (secs)" and since i have so many tuners and since they are rarely all in use, then would that mean I would only rarely have "back-to-back recordings on the same input"?  An input = a tuner meaning I have 6 inputs?  And so even the programs taped in the middle of a long run of tapings will be OK?
I think I would prefer to do it that way.  I'd rather not have to set it for each recording, nor at 

Actually I just looked now, and am more confused to see method 1 is part of the frontend, because I didn't realize that frontends could control what I thought were backend recording properties, and I don't understand the idea of setting this setting on a per frontend basis.  Does mythweb scheduling have access to set these properties?  Or settings timers from kodi?

For method 2, I haven't yet figured out many of Myth's settings under mytheb > Advanced Options, would Is it possible to default the mythweb web form "End late" field to 1 minute?