Getting ffmpeg output with QProccess

rktech

I have this code in QT:

#include <QCoreApplication>
#include <QProcess>
#include <QDebug>
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QProcess p;
    QString ba;
    QString exec = "ffmpeg.exe";
    QStringList params;
    params << " -i S01E01.mp4 2>&1";
    p.start(exec, params);
    p.waitForFinished(); // sets current thread to sleep and waits for p end
    QString output(p.readAllStandardOutput());
    qDebug()<<output;
    return a.exec();
}

When I ran the command directly I get this:
ffmpeg.exe -i S01E01.mp4 2>&1
ffmpeg version git-2020-04-24-a501947 Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 9.3.1 (GCC) 20200328
configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
libavutil 56. 42.102 / 56. 42.102
libavcodec 58. 81.100 / 58. 81.100
libavformat 58. 42.101 / 58. 42.101
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 79.100 / 7. 79.100
libswscale 5. 6.101 / 5. 6.101
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'S01E01.mp4':
Metadata:
major_brand : mp42
minor_version : 512
compatible_brands: isomiso2avc1mp41
creation_time : 2017-01-01T15:13:24.000000Z
title : The Simpsons S01E01 Simpsons Roasting on an Open Fire
encoder : HandBrake 0.10.5 2016021100
Duration: 00:23:12.98, start: 0.000000, bitrate: 247 kb/s
Chapter #0:0: start 0.000000, end 18.282000
Metadata:
title : Chapter 1
Chapter #0:1: start 18.282000, end 334.488000
Metadata:
title : Chapter 2
Chapter #0:2: start 334.488000, end 584.364000
Metadata:
title : Chapter 3
Chapter #0:3: start 584.364000, end 831.534000
Metadata:
title : Chapter 4
Chapter #0:4: start 831.534000, end 1314.951000
Metadata:
title : Chapter 5
Chapter #0:5: start 1314.951000, end 1392.930000
Metadata:
title : Chapter 6
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/smpte170m/bt709), 480x360, 191 kb/s, 30.30 fps, 30.30 tbr, 90k tbn, 60.61 tbc (default)
Metadata:
creation_time : 2017-01-01T15:13:24.000000Z
handler_name : VideoHandler
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 49 kb/s (default)
Metadata:
creation_time : 2017-01-01T15:13:24.000000Z
handler_name : Mono
Stream #0:2(eng): Data: bin_data (text / 0x74786574)
Metadata:
creation_time : 2017-01-01T15:13:24.000000Z
handler_name : SubtitleHandler
At least one output file must be specified

But when I run it using the code mentioned before, I get "". What I am doing wrong?

SGaist

params << "-i" << "S01E01.mp4"

In any case, "2>&1" is command prompt specific, so it does not make sense to put it there and might even interfere.

SGaist

Hi,

Remove the channel handling at the end of the command.
Also the proper way to pass parameters is to build a QStringList with each element separately.

rktech

@SGaist

params << " -i"<<" S01E01.mp4";

Still nothing

SGaist

Is that video file located in the same folder as the executable ?
You should also check whether the command failed and its standard erreur channel.

rktech

@SGaist

Is that video file located in the same folder as the executable ?

Yes, it is like this

You should also check whether the command failed and its standard erreur channel.

How?

SGaist

QProcess::readStandardError
QProcess:exitCode
QProcess::exitStatus

rktech

@SGaist How to correctly use readStandartError? Print in qDebug?

rktech

@rktech exitStatus: QProcess::NormalExit, exitCode: 1

SGaist

@rktech said in Getting ffmpeg output with QProccess:

@SGaist How to correctly use readStandartError? Print in qDebug?

That's one way yes.

rktech

@rktech readStandartError
ffmpeg version git-2020-04-24-a501947 Copyright (c) 2000-2020 the FFmpeg developers\r\n built with gcc 9.3.1 (GCC) 20200328\r\n configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf\r\n libavutil 56. 42.102 / 56. 42.102\r\n libavcodec 58. 81.100 / 58. 81.100\r\n libavformat 58. 42.101 / 58. 42.101\r\n libavdevice 58. 9.103 / 58. 9.103\r\n libavfilter 7. 79.100 / 7. 79.100\r\n libswscale 5. 6.101 / 5. 6.101\r\n libswresample 3. 6.100 / 3. 6.100\r\n libpostproc 55. 6.100 / 55. 6.100\r\n[NULL @ 0000024fd452b800] Unable to find a suitable output format for ' -i'\r\n -i: Invalid argument\r\n

I would drop error, but same as in my first post.

rktech

@rktech That was caused by splitting parametrs into list, but the problem with wrong error continues:
"ffmpeg version git-2020-04-24-a501947 Copyright (c) 2000-2020 the FFmpeg developers\r\n built with gcc 9.3.1 (GCC) 20200328\r\n configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf\r\n libavutil 56. 42.102 / 56. 42.102\r\n libavcodec 58. 81.100 / 58. 81.100\r\n libavformat 58. 42.101 / 58. 42.101\r\n libavdevice 58. 9.103 / 58. 9.103\r\n libavfilter 7. 79.100 / 7. 79.100\r\n libswscale 5. 6.101 / 5. 6.101\r\n libswresample 3. 6.100 / 3. 6.100\r\n libpostproc 55. 6.100 / 55. 6.100\r\nOutput #0, mp4, to ' -i S01E01.mp4':\r\nOutput file #0 does not contain any stream\r\n"

SGaist

Try removing the spaces in the parameter list.

rktech

Done like this:

params << "-i S01E01.mp4 2>&1";

Getting this error:
"ffmpeg version git-2020-04-24-a501947 Copyright (c) 2000-2020 the FFmpeg developers\r\n built with gcc 9.3.1 (GCC) 20200328\r\n configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf\r\n libavutil 56. 42.102 / 56. 42.102\r\n libavcodec 58. 81.100 / 58. 81.100\r\n libavformat 58. 42.101 / 58. 42.101\r\n libavdevice 58. 9.103 / 58. 9.103\r\n libavfilter 7. 79.100 / 7. 79.100\r\n libswscale 5. 6.101 / 5. 6.101\r\n libswresample 3. 6.100 / 3. 6.100\r\n libpostproc 55. 6.100 / 55. 6.100\r\nUnrecognized option 'i S01E01.mp4 2>&1'.\r\nError splitting the argument list: Option not found\r\n"

rktech

The

2>&1

Is not the problem, it drops same error without it.

SGaist

params << "-i" << "S01E01.mp4"

In any case, "2>&1" is command prompt specific, so it does not make sense to put it there and might even interfere.

rktech

@SGaist Thanks, now it works