[mythtv-users] Curious fast forward problem
Michael T. Dean
mtdean at thirdcontact.com
Thu Jan 7 02:36:36 UTC 2021
On 01/06/2021 04:36 PM, Michael T. Dean wrote:
> On 01/06/2021 03:54 PM, Peter Bennett wrote:
>>
>> On 1/5/21 11:56 AM, mythtv wrote:
>>> We've been experiencing this weird fast forward behaviour for
>>> several versions now. I assume it must just be something we're doing
>>> wrong because it's never changed since at least v0.28 and no one
>>> else seems to be talking about it.
>>>
>>> What happens is this: We have auto-skip commercials turned off. When
>>> watching live tv, if we're delayed for more than a few minutes, then
>>> hit fast-forward to manually skip thru some commercials, 9 out of 10
>>> times, we can skip thru a few commercials but sometimes it will
>>> just jump forward to almost live again (a few seconds behind live).
>>> I hope I explained that correctly. Its not "consistent" but it
>>> happens frequently enough to be a real nuisance, especially when our
>>> remote doesn't have numbers allowing us to just jump back a certain
>>> number of minutes. And also, the amount jumped is not a consistent
>>> amount of time, it always just jumps to near live again. I believe
>>> the backend is marking commercial breaks, and maybe there is some
>>> weirdness in trying to jump forward without a correct number of
>>> commercial breaks recorded, or some other setting about the length
>>> of commercials, etc. I don't quite understand all of those settings,
>>> and I don' think I've changed any from the defaults, other than to
>>> disable commercial auto-skip.
>>>
>> I have noticed this when watching a program that is still recording.
>> As you mention, it has been around for a long time. The biggest
>> problem with fixing it is that it is so intermittent. In my
>> experience it only happens maybe one time out of every 10 programs
>> watched while recording. It seems to happen occasionally when I am
>> around 15 minutes before the end, on a single skip forward it jumps
>> to the end instead of jumping 1 minute. It is not related to marking
>> commercial breaks. I believe it is something wrong with the way the
>> system keeps track of the increasing program size and the amount
>> remaining. If you can identify how to reproduce it, maybe we can
>> solve it.
>
> Are you sure that the frontend just hasn't gotten an update to the
> currently-detected commercial skiplist and, perhaps, the last update
> it received was one with a commercial start but without its
> accompanying commercial end? Basically it received an update while
> the commercial detection was inside a commercial break (so the last
> mark was a MARK_COMM_START ) and the backend hasn't sent out an update
> that includes the MARK_COMM_END ?
>
> IIRC, I think the COMMFLAG_UPDATE event tends to be sent (to any
> frontends that requested updates for that program with a
> COMMFLAG_REQUEST event) every 500 frames or so of commercial
> detection, so that would be around 8m 20s of actual program time for a
> 60fps show, but depending on how busy/powerful the system running the
> commercial detection is and depending on how far it's trying to stay
> away from the "now" of the recording, I could see how it could be
> 10+min behind now. For interlaced video, I'm not sure if it's
> actually frames or fields, but if it's still 500 frames, an update
> would be sent after processing about 16m 40s of recording in a 1080i60
> show, for example.
>
> It's possible that when the flagger recomputes the commercial skip
> list, it ensures it never ends with a MARK_COMM_START, in which case
> this shouldn't be the problem, but I haven't looked.
>
> Anyway, just a thought. If nothing else, something like this could
> explain the intermittency of the issue. Feel free to ignore me if my
> guess is way off, though. :)
Jeremy's last message that he's had real-time commflag disabled seems to
indicate it's not the commercial skip list, so ignore. I don't know how
the player/recorder handle seek table updates, but I'd assume they're
not nearly so infrequent as COMMFLAG_UPDATEs.
Mike
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