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The pirate bay depuis la Belgique
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How correctly show video with transparency in Qt with OpenCV + FFMpeg
11 avril 2022, par TheEnigmistI'm trying to show a video with transparency in a Qt6 application using OpenCV + FFMPEG.
Actually those are tool versions :


- 

- Win 11
- Qt 6.3.0
- OpenCV 4.5.5 (built with CMake)
- FFMPEG 2022-04-03-git-1291568c98-full_build-www.gyan.dev










I've used a base .mov video with transparency as test (link provided below).
First of all I've converted .mov video to .webm video (VP9) and I see in output text that alpha channel remains




ffmpeg -i '.\Retro Bars.mov' -c:v libvpx-vp9 -crf 30 -b:v 0 output.webm




Input #0, mov,mp4,m4a,3gp,3g2,mj2,
 ...
 Stream #0:0[0x1](eng): Video: qtrle (rle / 0x20656C72), argb(progressive),
 ...

Output #0, webm, 
 ...
 Stream #0:0(eng): Video: vp9, yuva420p(tv, progressive),
 ...



But when I show info of output file with ffmpeg it loses alpha channel :




ffmpeg -i .\output.webm




Input #0, matroska,webm,
 ...
 Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv, progressive),
 ...



If I open output.webm with OBS it is shown correctly without a background, as shown in picture :



If I try to open it with OpenCV + FFMPEG it shows a black background under bars, as shown in picture :



This is how I load video in Qt :


cv::VideoCapture capture;
capture.open(filename, cv::CAP_FFMPEG);
capture.set(cv::CAP_PROP_CONVERT_RGB, false); // try forcing load alpha channel
... //in a thread
while (capture.read(frame)) {
 qDebug() << "c" << frame.channels() << "t" << frame.type() << "d" << frame.depth(); // output: c 3 t 16 d 0
 cv::cvtColor(frame, frame, cv::COLOR_BGR2RGBA); //useless since no alpha channel is detected
 img = QImage(frame.data, frame.cols, frame.rows, QImage::Format_RGBA8888);
 emit processedImage(img); // to show image in a QLabel with QPixmap::fromImage(img)
}



I think the problem is when I load the video with OpenCV, it doens't detect alpha channel, since I can load correctly in other player (obs, html5, etc.)


What I'm wrong with all process to show this video in Qt with transparency ?


EDIT : Added dropbox link with test video + ffmpeg outputs :
sample items


-
"wrong sample count" When reading MP4 files using OpenCV
26 octobre 2022, par Object UnknownI want to marge some mp4 videos using OpenCV library, but when I try to read those videos using
cv::VideoCapture
, it outputs like that :

[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9AAE9D80] co located POCs unavailable
[h264 @ 000001EB9AAE7D80] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9A128600] co located POCs unavailable
[h264 @ 000001EB9A129840] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB9AA28E40] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9A169B00] co located POCs unavailable
[h264 @ 000001EB9A16B680] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB960CD680] co located POCs unavailable
[h264 @ 000001EB960CC8C0] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9A81DDC0] co located POCs unavailable
[h264 @ 000001EB9A81B000] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB960CB200] co located POCs unavailable
[h264 @ 000001EB960CBFC0] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB99F206C0] co located POCs unavailable
[h264 @ 000001EB99F20B40] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9A81D480] co located POCs unavailable
[h264 @ 000001EB9A81B000] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9AD02C00] co located POCs unavailable
[h264 @ 000001EB9AD02300] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9A81B480] co located POCs unavailable
[h264 @ 000001EB9A81B940] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[h264 @ 000001EB9AD02780] co located POCs unavailable
[h264 @ 000001EB9AD01E40] co located POCs unavailable
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001EB96084B80] wrong sample count



and just exited with exit value 0. I want to know why it is reporting this and how to solve it please.


Heres my demo code :


#include <string>
#include <iostream>
#include <opencv2></opencv2>core/core.hpp>
#include <opencv2></opencv2>video/video.hpp>
#include <opencv2></opencv2>imgproc/imgproc.hpp>
#include <opencv2></opencv2>videoio/videoio.hpp>
#include <opencv2></opencv2>highgui/highgui.hpp>

int main()
{
 cv::Mat frame;
 cv::VideoCapture vcap;
 for (int i = 1; i <= 60; i++)
 {
 if (!vcap.open("G:\\Users\\15819\\Desktop\\Demo\\demo (" + std::to_string(i) + ").mp4"))
 {
 std::cout << "Failed to Open File: demo (" << i << ").mp4" << std::endl;
 continue;
 }
 while (!vcap.read(frame))
 cv::imshow("video", frame);
 }
 return 0;
}
</iostream></string>


I installed the
OpenCV
andFFmpeg
library usingvcpkg
, here's the library information (displayed byvcpkg list
command) :

ffmpeg:x64-windows 4.4.1#21 a library to decode, encode, transcode, mux, dem...
ffmpeg:x86-windows 4.4.1#21 a library to decode, encode, transcode, mux, dem...
ffmpeg[avcodec]:x64-windows Build the avcodec library
ffmpeg[avcodec]:x86-windows Build the avcodec library
ffmpeg[avdevice]:x64-windows Build the avdevice library
ffmpeg[avdevice]:x86-windows Build the avdevice library
ffmpeg[avfilter]:x64-windows Build the avfilter library
ffmpeg[avfilter]:x86-windows Build the avfilter library
ffmpeg[avformat]:x64-windows Build the avformat library
ffmpeg[avformat]:x86-windows Build the avformat library
ffmpeg[openh264]:x64-windows H.264 de/encoding via openh264
ffmpeg[openh264]:x86-windows H.264 de/encoding via openh264
ffmpeg[swresample]:x64-windows Build the swresample library
ffmpeg[swresample]:x86-windows Build the swresample library
ffmpeg[swscale]:x64-windows Build the swscale library
ffmpeg[swscale]:x86-windows Build the swscale library
opencv4:x64-windows 4.6.0#6 computer vision library
opencv4:x86-windows 4.6.0#6 computer vision library
opencv4[default-features]:x64-windows Platform-dependent default features
opencv4[default-features]:x86-windows Platform-dependent default features
opencv4[dnn]:x64-windows Enable dnn module
opencv4[dnn]:x86-windows Enable dnn module
opencv4[ffmpeg]:x64-windows ffmpeg support for opencv
opencv4[ffmpeg]:x86-windows ffmpeg support for opencv
opencv4[jpeg]:x64-windows JPEG support for opencv
opencv4[jpeg]:x86-windows JPEG support for opencv
opencv4[png]:x64-windows PNG support for opencv
opencv4[png]:x86-windows PNG support for opencv
opencv4[qt]:x64-windows Qt GUI support for opencv
opencv4[qt]:x86-windows Qt GUI support for opencv
opencv4[quirc]:x64-windows Enable QR code module
opencv4[quirc]:x86-windows Enable QR code module
opencv4[tiff]:x64-windows TIFF support for opencv
opencv4[tiff]:x86-windows TIFF support for opencv
opencv4[webp]:x64-windows WebP support for opencv
opencv4[webp]:x86-windows WebP support for opencv
opencv:x64-windows 4.6.0 Computer vision library
opencv:x86-windows 4.6.0 Computer vision library
opencv[default-features]:x64-windows Platform-dependent default features
opencv[default-features]:x86-windows Platform-dependent default features
opencv[dnn]:x64-windows Enable dnn module
opencv[dnn]:x86-windows Enable dnn module
opencv[jpeg]:x64-windows JPEG support for opencv
opencv[jpeg]:x86-windows JPEG support for opencv
opencv[png]:x64-windows PNG support for opencv
opencv[png]:x86-windows PNG support for opencv
opencv[quirc]:x64-windows Enable QR code module
opencv[quirc]:x86-windows Enable QR code module
opencv[tiff]:x64-windows TIFF support for opencv
opencv[tiff]:x86-windows TIFF support for opencv
opencv[webp]:x64-windows WebP support for opencv
opencv[webp]:x86-windows WebP support for opencv



Other Environments :


OS: Windows 11 x64 Professional Workstation
IDE: Visual Studio 2022
Project C++ Standard: C++14
Project Platform: x64 Release



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