Creating a video file in Qt

mrjj

Hi
For fast way, i would just use ffmpeg
http://hamelot.io/visualization/using-ffmpeg-to-convert-a-set-of-images-into-a-video/
with QProcess.

As creating a mp4 from scratch is pretty involving due to codex compressing and all the header info.

ffmpeg runs on linux, mac and windows so its only if u use android it would be a bad idea.

Pablo J. Rogina

@NIXIN what about trying with a QML Camera component?

NIXIN

@mrjj Thanks for your response. Based on your suggestion I tried this:

void Video::slot_generateVideo()
{
QStringList arguments;
QString imgPath("home/uidm9805/images/pic%04d.png");
int fps = 2;
QString frameRate;
QString compressionLevel("image2");
QString resolution("1920x1080");
QString startFrame("1");
QString videoFrames("1000");
QString codec("libx264");
QString quality("25");
QString pixelFormat("yuv420p");
QString outputFile("\"home/uidm9805/images/test.mp4\"");

arguments << "-r";
arguments << frameRate.setNum(fps);

arguments << "-f";
arguments << compressionLevel;

arguments << "-s";
arguments << resolution;

arguments << "-start_number";
arguments << startFrame;

arguments << "-i";
arguments << imgPath;

arguments << "-vframes";
arguments << videoFrames;

arguments << "-vcodec";
arguments << codec;

arguments << "-crf";
arguments << quality;

arguments << "-pix_fmt";
arguments << pixelFormat;

arguments << outputFile;

qDebug() << arguments;
videoProcess = new QProcess(this);
connect(videoProcess, SIGNAL(started()), this, SLOT(monitorStarted()));
connect(videoProcess, SIGNAL(error(QProcess::ProcessError)), this, SLOT(monitorError(QProcess::ProcessError)));
connect(videoProcess, SIGNAL(readyReadStandardOutput()), this, SLOT(readOutput()));
videoProcess->start("ffmpeg", arguments);
videoProcess->waitForFinished(-1);
}

void Video::monitorStarted()
{
    qDebug() << "Video Process started";
}

void Video::monitorError(QProcess::ProcessError error)
{
    qDebug() << "Video Process error: " << error;
}

void Video::readOutput()
{
    qDebug() << videoProcess->readAllStandardOutput();
}

I am working on ubuntu.
when I run the same set of commands from terminal everything is working fine, test.mp4 is generated.
But using QProcess, I got this output:
Video Process error: 0
I don't understand what might be the problem, any help will be appreciable.
Thank you

jsulm

@NIXIN "QString imgPath("home/uidm9805/images/pic%04d.png");" you're missing / in front of home. Also why do you have % in file name?
Same here QString outputFile("\"home/uidm9805/images/test.mp4\""); and remove \" as Qt will do it for you.

NIXIN

I tried giving the following paths:

QString folderName ="images/pic"
QString imgPath("/home/uidm9805/" + folderName + "%04d.png");
QString outputFile("/home/uidm9805/images/test.mp4");

still not working, getting same errors

mrjj

Hi
Code seems fine.
try with full path to ffmpeg
also
folderName ="images/pic"

Depending on how it uses this, it might not be correct.

NIXIN

@mrjj
Tried this

videoProcess->start("usr/bin/ffmpeg", arguments);

but got the same errors.

NIXIN

@mrjj

folderName ="images/pic"

Depending on how it uses this, it might not be correct.

Can you explain this please.....

mrjj

@NIXIN

If something just appends that to other path or use it relative,
it might not work as expected.
Like
somewhere = "/home"
open (somewhere + folderName )
"/homeimages/pic"
and so one.
but if it adds / when doing + , all is fine.

since there is no error reported with QProcess i assume it runs the app but app do not produce output for some reason.

SGaist

Hi,

You are missing the leading / in your path to ffmpeg.

jsulm

@NIXIN said in Creating a video file in Qt:

usr/bin/ffmpeg

Please take a closer look at the path. You're doing same mistake over and over even after it was pointed out.

Vijaykarthikeyan

@NIXIN you can use opencv to write the frames into .avi or any other format you want to write.