QtCam Application Build issue in Ubuntu 18.04

[fadhel086]

when building the application as mentioned in INSTALL doc:

Using Console:

1. Goto your git clone path.
2. cd src/
3. Set LAUNCHPAD macro in common.h to 0.
4. qmake --->

response obtained is
No LSB modules are available.
Project MESSAGE: x86_64 bit libs
Project ERROR: Unknown module(s) in QT: multimedia qml quick

Similarly when installing dependencies the following error is obtained:
E: Unable to locate package qtdeclarative5-dialogs-plugin
E: Unable to locate package qtdeclarative5-qtmultimedia-plugin

[e-consystemgit]

The above packages "qtdeclarative5-dialogs-plugin" and "qtdeclarative5-qtmultimedia-plugin" will not have support in 18.04 .Instead of it you can install "qml-module-qtquick-dialogs" and "qml-module-qtquick-extras" packages to get rid of project Error it shown.We updated the INSTALL file with these packages.You can refer it in case of any doubt.

[Ravisurya-VN]

I am trying to compiler qtcam sample camera application on the ubuntu 18.04 LTS version. I am also using Logitech HD Webcam C310 as it is one of the supported USB 2.0 Cameras by the application.

My development environment looks like below:-
HOST : Ubuntu 18.04 LTS
Qt Version : 5.11.3
Compiler: gcc x86 64

I have two questions :-
Q1 : - When I set the LAUNCHPAD as 0, the application builds fine and launches the application also fine but the camera view is not showing up. Please let me know what could be the problem.

Q2:- I also have target IMX7 embedded board for which I have the
compiler:- arm-linux-generic-elf-32bit
Qt: 5.11.3
I have also installed gstreamer good,bad ,ugly and gstream1.0-libav packages, when compiled for the target I am getting error as "libavcodec/avcodec.h is not a file or a directory", how to fix this issue?