<div dir="ltr">It is probably related to how turbo boost works. You need to tune your OS for CPU latency (governor performance on Debian/Ubuntu), it has to do with the delay changing between low power states and performance states. When you sleep continuously, you cannot reach peak CPU clock speed. When you don't use the sleep, you are using peak clock speed all the time.<div><br></div><div>Cheers,</div><div><br></div><div>Omar. </div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">El sáb., 1 jun. 2019 a las 19:33, Paul Sanderson (<<a href="mailto:nannapie@hotmail.co.uk">nannapie@hotmail.co.uk</a>>) escribió:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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I think Carl’s point is interesting. It could be something funky with sleep which if I remember right is a Linux/ Debian based call. Maybe try a different method of making your program hang and see if the problem persists.
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<div>All my best,</div>
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<div>Paul <br>
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<div id="gmail-m_1335320627791674332AppleMailSignature" dir="ltr">Sent from the top a castle using a moderately sized European swallow </div>
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On 1 Jun 2019, at 16:17, Lukas Bommes <<a href="mailto:lukas.bommes@gmx.de" target="_blank">lukas.bommes@gmx.de</a>> wrote:<br>
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<div>I'm just buffled because OpenCV uses the same code <span style="font-family:sans-serif"> (in fact I copied the retrieveFrame funtion from the videoio module 1:1)</span> and it does not show this weird behaviour. There, the runtime of sws_scale is constant
regardless of the calling frequency and retrieving one frame takes always around 1.3 ms.</div>
<div dir="auto">However, my OpenCV build (version 4.1) uses FFMPEG 3.4.6, not 4.1. So, I'm gonna try building my code with FFMPEG 3.4.6 and see if the problem persists. </div>
<div dir="auto">Alternatively, I add a function to the OpenCV videoio module which retrieves frame + motion vectors. However, altering the OpenCV API brings a lot of other challenges.</div>
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<div dir="auto">But maybe someone else has noticed a similar issue with sws_scale in FFMPEG 4.1 before.</div>
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<div class="gmail_extra" dir="auto">Lukas</div>
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<div class="gmail_quote">On 1 Jun 2019 7:04 pm, Carl Eugen Hoyos <<a href="mailto:ceffmpeg@gmail.com" target="_blank">ceffmpeg@gmail.com</a>> wrote:<br type="attribution">
<blockquote class="gmail-m_1335320627791674332quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<p dir="ltr">Am Do., 30. Mai 2019 um 11:59 Uhr schrieb lukas <<a href="mailto:lukas.bommes@gmx.de" target="_blank">lukas.bommes@gmx.de</a>>:</p>
<p dir="ltr">> I wrote a program which extracts motion vectors from a video stream and<br>
> encountered the problem that the runtime of sws_scale changes depending<br>
> on whether I put a sleep command in the main loop of the caller.</p>
<p dir="ltr">Shouldn't you ask this your CPU provider?</p>
<p dir="ltr">Carl Eugen<br>
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