why QMediaPlayer can not play from QThread?

Mozzie

I am trying to play vedio file from another thread, but got application crash, and after i using windbg to analyze dump file , I found following message:

FAILURE_BUCKET_ID: NULL_POINTER_READ_c0000005_dsengine.dll!Unknown

//////////////////////////////////.h
#ifndef TESTMEDIAPLAYER_H
#define TESTMEDIAPLAYER_H

#include <QObject>
#include <QMediaPlayer>

class TestMediaPlayer : public QObject
{
	Q_OBJECT
	QMediaPlayer* player = nullptr;
public:
	explicit TestMediaPlayer(QObject *parent = nullptr);

signals:
	void play();
};

#endif // TESTMEDIAPLAYER_H
//////////////////////////////////.h

//////////////////////////////////cpp
#include "TestMediaPlayer.h"

TestMediaPlayer::TestMediaPlayer(QObject *parent) : QObject(parent)
{

	player = new QMediaPlayer(this);

	connect(this, &TestMediaPlayer::play, this, [this](){
		player->setMedia(QUrl::fromLocalFile("2021_05_06_10_59_00.flv"));
		player->play();
	}, Qt::QueuedConnection);
}
//////////////////////////////////cpp

//////////////////////////////////gui.cpp

		TestMediaPlayer* test = new TestMediaPlayer();

		QThread* thread = new QThread;
		test->moveToThread(thread);
		thread->start();

		test->play();
//////////////////////////////////gui.cpp

thanks for your help

SGaist

Hi,

QMediaPlayer will render video data which is a GUI activity. This can only happen in the GUI thread.
There might also be backends that do not support that kind of setup.

Mozzie

@SGaist
thank you very much

Mozzie

@SGaist
hello, can I ask more question?
today, I test two different version of Qt with the same code,
and I found my code will crash on Qt5.12.10 but on Qt5.14.2, It would work.
Is there any bug on Qt5.12 or something changed after Qt5.12, I read changed logs from Qt5.13.0 to Qt5.14.2 but could not notice which change will cause this.

Kent-Dorfman

If it crashes on 12 then it's problably wrong on 14 as well. 14 may just be more tolerant of your bugs.

jsulm

@Mozzie You should post the stack trace after crash, else only guessing is possible.

Mozzie

@Kent-Dorfman @SGaist @jsulm

emmm.... you are right, today I find more evidence.

I found, my system is diffirent from my colleague. they are using win10 home or win10 professional version, my system is "win10 Enterprise ltsc" and they can run my code without crash. and I also installed two version of win10 in my virtualbox software. and also my code just crash on "win10 Enterprise ltsc"

Mozzie

@jsulm
thank you. this is a good idea
I had create windows dump file, could you tell me what information is helpful and I am using windbg debug tool

jsulm

@Mozzie Useful is the stack trace