C++ & Qt

14 November 2025 22:43

Just point at Big Buck Bunny — it's commonly used for testing video stuff.

C++ & Qt

14 November 2025 19:58

When I copy the frame into a new image (with QPainter) and then save this new picture, everything is as expected.

C++ & Qt

14 November 2025 19:56

Have you guys seen this?

C++ & Qt

14 November 2025 19:55

I'm not really sure what causes this.

C++ & Qt

14 November 2025 19:53

But sounds reasonable! 😊

C++ & Qt

14 November 2025 19:25

I wrote a suggestion for Qt: https://bugreports.qt.io/browse/QTBUG-141989

C++ & Qt

14 November 2025 19:19

I'd probably implement it with grabbing the frame whenever it changes and then drawing it after rotation in the paint event.

C++ & Qt

14 November 2025 19:18

Funny coincidence! 😉

C++ & Qt

14 November 2025 19:16

I investigated this a bit last night and this morning, and I haven't figured out a good way to do this.

The way to do this that is most optimized would be to do the video playback in Qt Quick, and embed it in your Widgets app using a QQuickWidget — this way you get optimized rendering.

I don't know of a "pure widgets" way to do it, but another way that occurred to me is to do it in a QGraphicsScene - as that provides a way to transform Qt Widgets.

C++ & Qt

13 November 2025 18:34

Hey - question about video playback. How do you change orientation of the video? I couldn't find anything to that end in QMediaPlayer or QVideoSink.

C++ & Qt

12 November 2025 14:22

and interesting thing: if you make the same set and pass func as simple i64* ptr — it may be optimized and may be optimized completely if you use instead of vector<> MyStruct*

C++ & Qt

12 November 2025 09:40

but this is preference, not reliable. use constexpr or templates hell (but it's crazy)

C++ & Qt

12 November 2025 09:38

and x3 mem, but for small arrs copy approach is the best

C++ & Qt

12 November 2025 09:34

never overuse constexpr or templates

calc, save to file, read. — anything that's faster can be cached, etc

C++ & Qt

11 November 2025 22:42

I think this does it all at compile time:

#include <ranges>
#include <array>
#include <iostream>

auto evenArray = std::views::iota(0, 10) | std::views::filter([](const auto& even) { return even % 2 == 0; })
        | std::ranges::to<std::array>();

static_assert(even_numbers.size() == 5, "Incorrect size");

C++ & Qt

14 November 2025 22:43

https://github.com/keithel/multimedia-video-modify-orientation

C++ & Qt

14 November 2025 19:57

Looks to me as if color spaces are off.

C++ & Qt

14 November 2025 19:56

Unfortunately, I don't have a video right now that I could share for a bug report.

C++ & Qt

14 November 2025 19:55

A separate observation: When grabbing a frame and saving it to disk (as a png or jpg), for SOME videos, the saved image will be much brighter than the video.

C++ & Qt

14 November 2025 19:49

I suppose a QOpenGLWidget subclass could be more efficient

C++ & Qt

14 November 2025 19:20

But then, the playback isn't really optimized. It's then all software.

C++ & Qt

14 November 2025 19:18

But thanks - that would be great.

C++ & Qt

14 November 2025 19:17

I'll shoot a link to the repo I used for my testing... I haven't implemented the QGraphicsScene approach.

C++ & Qt

13 November 2025 18:35

If it doesn't exist, I'll just create a derived class that does. 😉

C++ & Qt

12 November 2025 14:26

some simple deobfuscation theory of handlers graph from simple stack base vm's that ommit scratch)

C++ & Qt

12 November 2025 13:46

btw, templates are a feature to copy-past functions with different type but where overload not enough

if you can't understand stl decl from a quick glance — you dont know them to use right. to say, few one can use them

C++ & Qt

12 November 2025 09:39

lambda'll break optimization chain to flatten it — inline pass, then check deps graph and precalc it

C++ & Qt

12 November 2025 09:36

and check disasm, it'll generate code

C++ & Qt

12 November 2025 08:41

Welcome to the group, @faddistyoungman! :-)

Wanna share your story of how you started with Qt, QML or C++? Maybe some nice feature that made you stick with it.
Rules are set on the description of the group. :)

C++ & Qt

11 November 2025 22:25

Other people of course may have different opinions about what can be "immediately understood"! 😊