[mythtv-users] Running mythcommflag on another PC?

Ian Evans dheianevans at gmail.com
Sun Mar 3 05:37:41 UTC 2024

On Sat, Mar 2, 2024 at 11:31 PM Ian Evans <dheianevans at gmail.com> wrote:

> On Sat, Mar 2, 2024 at 7:02 PM Stephen Worthington <
> stephen_agent at jsw.gen.nz> wrote:
>> As for mythcommflag performance, for processors 10 years old or
>> younger and not the super cheap variety, then they can normally do
>> commflagging on one recording per CPU core/thread in real time.  So
>> for a 4 core dual threaded CPU, you could do 8 mythcommflag processes
>> simultaneously in real time as 8 recordings happen together.  The
>> trick with real time commflagging is that it gets done in RAM, on the
>> buffered recording data before it gets written to disk.  Once the data
>> has been written to disk, reading it back again slows down
>> commflagging, as there is then the problem of contention for the disk,
>> with the heads having to move between recordings.  So you also need
>> enough RAM, as well as the CPU resources.
>> I gave up doing commflagging a long time ago as here in New Zealand,
>> it never gave useful results.  So I have not tried commflagging with
>> the current generations of CPU, which are much faster again than 10
>> year old ones.  They may well be able to do more than one mythcommflag
>> operation per CPU thread, maybe even three or four.
>> I would recommend a starting position of one commflag operation per
>> CPU core/thread being run on the main recording box, starting the
>> commflagging when the recording starts.  Then just let any more
>> simultaneous recordings that go over that limit have their
>> commflagging queued to be done later.  There should not be any need to
>> have another box doing commflagging unless you are recording 20 things
>> at once all day.
> Just a quick background. My wife and I are currently working on another
> place and I've just MacGyver'd a temporary setup so we'd have a PVR and I
> could tiner with v34.
> The backend is currently running on an old Toshiba Satellite laptop. It
> has 8 gig of RAM and a i7-3720QM CPU.
> According to Intel ARK:
>    - Total Cores 4
>    - Total Threads 8
>    - Max Turbo Frequency 3.60 GHz
>    - Intel® Turbo Boost Technology 2.0 Frequency‡ 3.60 GHz
>    - Processor Base Frequency 2.60 GHz
>    - Cache 6 MB Intel® Smart Cache
> When I tried running commercial detection a few months ago, I remember the
> load spiking to 2.00. Can't remember if I had that running post recording
> while there were other recordings. I may have not set it for real-time
> detection thinking a laptop couldn't handle it. I'll have to change the
> setup when my the SVU marathon is over.

An update. Went into setup and allowed commercial detection to start
immediately. CPU setting was Low.

Created a 15 minute manual recording a few minutes away and allowed
commercial detection for that recording. The recording started.

According to the queue it first looked up the metadata and then ran
mythcommflag. According to top, load spiked to 3.97, and mythcommflag's CPU
% was around 97%. During the whole 15 minutes of the recording it never got
past "looking for logo:

When the recording ended, it finally started processing. Load dropped down
to about 1.75 and CPU% for mythcommflag was around 37%. According to the
job queue it was running at about 97.0251 fps.

Why would the logo detection spike so high?
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