[mythtv] Jumpy video playback

[Klaas de Waal]

On Sun, 12 Jan 2020 at 10:43, Klaas de Waal <klaas.de.waal at gmail.com> wrote:

>
>
> On Sat, 11 Jan 2020 at 01:18, Peter Bennett <pb.mythtv at gmail.com> wrote:
>
>>
>>
>> On 1/9/20 5:36 PM, Klaas de Waal wrote:
>> > Hi Mark,
>> >
>> > My MythTV production system recorded this weekend a program that does
>> > not play back correct on my frontend with the Nvidia GT520  (driver
>> > version 340).
>> > It looks to me that the frame ordering is not correct; it jumps every
>> second.
>> > The complete recording of 10GB has this when played to the end.
>> > However, if I cut off the first GB or so from the file then what
>> > remains plays perfect.
>> > Also, when I play it back on my development system (Intel only) then
>> > the playback is smooth.
>> > If you are interested then I can send you the file (or the first 100MB
>> of it).
>> > Please let me know and also how you want it (WeTransfer or gmail
>> > attachment is what I use most of the time).
>> >
>> > Groetjes,
>> > Klaas.
>> > _______________________________________________
>> >
>>
>> I have noticed this type of behavior, but only on some reruns of
>> Midsomer Murders from early 2000's. It is especially bad on the
>> "Ovation" channel. I suspect some issue with the source, particularly
>> since I saw similar things when watching Midsomer Murders on Amazon
>> Prime with the prime app on NVidia Shield.
>>
>>
>> Peter
>> _______________________________________________
>>
>> I got a bit further on this; the problem is in the frame rate!
> It looks like that the recording is incorrectly identified as 24Hz instead
> of as 50Hz.
>
> When everything is OK it works like this as I understand it:
> (1) Broadcast signal is 50Hz interlaced
> (2) The playback info box shows this as 25.00fps
> (3) De-interlacing then generates 50 fps.
> (4) The Nvidia driver is set to 50Hz by MythTV/xrandr
> (5) This is shown in the System Status / Display box (very useful new
> addition)
> (6) The actual framerate is also shown on my TV as 50Hz
>
> With the problematic recording steps (1) to (3) are the same.
> The difference is:
> (4) The Nvidia driver is set to 23.98Hz by MythTV/xrandr
> (5) This is shown in the System Status / Display box (very useful new
> addition)
> (6) The actual framerate is also shown on my TV as 50Hz
>
> When the first 10 megabytes of the recording are removed then the playback
> is correct.
>
> This happened twice in the last two weeks in about 100 recordings or so.
> The broken recording is created with multirec; the previous recording on
> that
> channel was still running at the moment the new recording started.
> I have also in the past observed that the start of playback of recordings
> created
> by multirec has sometimes blocks.
>
> My tentative conclusion at this moment is:
> - there is something not correct in the first 10MB of the file
> - the frame rate is obtained from the first 10MB of the file
> - this frame rate is used to set the Nvidia with xrandr
> - later the correct frame rate is obtained as shown in the playback box
> - but the Nvidia framerate setting is never updated
>
>
> Typo correction: with the problematic recording the TV shows the actual
frame rate as 24Hz.
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