Qt Linux ad ffmpeg6

mrdebug

Hi, I have got an incomprensible linking problem with Linux (Debian 12) and ffmpeg 6.
This is my .pro file

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

INCLUDEPATH += ../../ffmpeg-6.0/
LIBS += ../../ffmpeg-6.0/libavcodec/libavcodec.a
LIBS += ../../ffmpeg-6.0/libavdevice/libavdevice.a
LIBS += ../../ffmpeg-6.0/libavfilter/libavfilter.a
LIBS += ../../ffmpeg-6.0/libavformat/libavformat.a
LIBS += ../../ffmpeg-6.0/libavutil/libavutil.a
#LIBS += ../../ffmpeg-6.0/libpostproc/libpostproc.a
LIBS += ../../ffmpeg-6.0/libswresample/libswresample.a
LIBS += ../../ffmpeg-6.0/libswscale/libswscale.a
LIBS += ../../ffmpeg-6.0/libavcodec/decode.o

SOURCES += \
    main.cpp \
    qfmainwindow.cpp

HEADERS += \
    qfmainwindow.h

FORMS += \
    qfmainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

but on linking time I obtain this error:

/home/denis/Cpp/ffmpegTest/ffmpegTest/main.cpp:-1: error: undefined reference to `avcodec_send_packet(AVCodecContext*, AVPacket const*)'

The libraries libavcodec.a and the others exist and there are in the right place.
I haven't got this type of error using the old version 4.2.2.

mrdebug

Hi, in order to use ffmpeg 6 libraries in a custom software it is mandatory to compile the source using this swich "--enable-pic"
and include the header in this way:

extern "C" {
    #include <libavutil/frame.h>
    #include <libavutil/mem.h>
    #include <libavcodec/avcodec.h>
}

kkoehne

@mrdebug said in Qt Linux ad ffmpeg6:

The libraries libavcodec.a and the others exist and there are in the right place.

But does it contain above exported symbol? You can check e.g. with nm -g | c++filt...

mrdebug

@kkoehne

denis@tomcat:~/Cpp/ffmpeg-6.0/libavcodec$ nm -g libavcodec.a | grep avcodec_send_packet
                 U avcodec_send_packet
0000000000001080 T avcodec_send_packet
                 U avcodec_send_packet
                 U avcodec_send_packet
                 U avcodec_send_packet
                 U avcodec_send_packet
denis@tomcat:~/Cpp/ffmpeg-6.0/libavcodec$

Christian Ehrlicher

I would take a look in the sources of ffmpeg if this function with the exact signature is in there or e.g. deprecated and therefore not compiled.

JoeCFD

@mrdebug
from here: https://ffmpeg.org/doxygen/3.1/avcodec_8h.html
The interface might have been changed.
avcodec_send_packet (AVCodecContext *avctx, const AVPacket *avpkt)

your call avcodec_send_packet(AVCodecContext*, AVPacket const*) is not right in the main.cpp. const is missed.

mrdebug

@JoeCFD Adding "const" has no affect.
By the way the problem is not at compile time but linking time.
I trying the 3 functions founded in the example ffmpeg-6.0/doc/examples/decode_video.c placed in a Qt empty project.

Christian Ehrlicher

Either you forward declared (wrongly) this function somewhere or you are using the wrong outdated headers.

JonB

@mrdebug

undefined reference to `avcodec_send_packet(AVCodecContext*, AVPacket const*)`

Since the last parameter ought be const AVPacket *, and (C++ expert correct me if I am wrong) AVPacket const * is not the same thing, I am with @Christian-Ehrlicher: start by searching all your sources and all that you include for avcodec_send_packet() declarations. Any chance it is incorrectly declared in one place?

JoeCFD

@JonB const AVPacket * means: const instance of AVPacket. Only const funcs of class AVPacket can be called.
AVPacket const * means: this is a constant pointer and its address can be changed.

Two different things.

mrdebug

The code is good because executing "make examples", the example from I have copied out the functions waw been compiled. I think the problem is related to some switch to add at the .pro file.

JoeCFD

@mrdebug the order of the libs matters. Change the order of static libs in the pro file.

JonB

@JoeCFD said in Qt Linux ad ffmpeg6:

Two different things.

I know. And the error message AVPacket const* does not match what it should be, which is const AVPacket *. Which make sit look like there is a declaration and call to AVPacket const* erroneously somewhere.

JonB

@JoeCFD said in Qt Linux ad ffmpeg6:

@mrdebug the order of the libs matters. Change the order of static libs in the pro file.

This is a good point. @mrdebug: do you call avcodec_send_packet() from your own code (e.g. main.cpp)? Because if not, and its internal, and you put libavcodec.a as the first library, and only a later library calls that function, it may not have been included. Do you get that order/list of linking the libraries from some documentation?

I haven't got this type of error using the old version 4.2.2.

Hmm ;-)

mrdebug

@JonB Hi, I have tried to edit the libraries order without any effect.
Now code is:

#include <libavutil/frame.h>
#include <libavutil/mem.h>
#include <libavcodec/avcodec.h>

int main(int argc, char *argv[])
{
    AVCodecContext *dec_ctx;
    AVPacket *pkt;
    avcodec_send_packet(dec_ctx, pkt);
    return 0;
}

and the .pro file is the one above. The error is the same:

/home/denis/Cpp/ffmpegTest/ffmpegTest/main.cpp:25: error: undefined reference to `avcodec_send_packet(AVCodecContext*, AVPacket const*)'

and to include only the library (libavcodec.a) that contains the function does not resolve.

JoeCFD

@mrdebug
Try the following

int main(int argc, char *argv[])
{
    AVCodecContext *dec_ctx{};
    const AVPacket *pkt{};
    avcodec_send_packet(dec_ctx, pkt);
    return 0;
}

or

int main(int argc, char *argv[])
{
    AVCodecContext *dec_ctx{};
    AVPacket * const pkt{};
    avcodec_send_packet(dec_ctx, pkt);
    return 0;
}

SGaist

@mrdebug hi,

Can you show the .pro file of your minimal project ?
Are you sure you are linking to the expected version of ffmpeg ?
Do you have your distribution provided ffmpeg development packages installed ?

mrdebug

@JoeCFD Tried both. The behaviour is the same.
Tomorrow I'll try on a Mac and Windows

mrdebug

Hi, in order to use ffmpeg 6 libraries in a custom software it is mandatory to compile the source using this swich "--enable-pic"
and include the header in this way:

extern "C" {
    #include <libavutil/frame.h>
    #include <libavutil/mem.h>
    #include <libavcodec/avcodec.h>
}