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Can I start Android App not in FullScreen mode?

I saw that youtube app can minimize to small window that displays over all other windows.
I want to do the same with my app.
What strings in manifest (or any other string) do it?
Thanks,
I am about this:

Take a look at google documentation about this topic, it is called picture-in-picture

You need to add the first two lines to your activity which will handle Picture in Picture (PIP) mode.
The third line needs to be added so that your activity will not relaunch once layout changes occur, such as device screen rotation.
android:resizeableActivity="true"
android:supportsPictureInPicture="true"
android:configChanges="screenSize|smallestScreenSize|screenLayout|orientation"
You can find more information about this in the android documentation.
Here is a tutorial on how to implement it.

You can refer to the following tutorials which are nice to understand
picture in picture feature
https://medium.com/#mujtahidah/making-picture-in-picture-android-4120ac73efb4
http://www.zoftino.com/android-picture-in-picture-mode-example

How do i make my android app accessible from the lockscreen?

I'm creating an app to be used during emergencies and it's important that the app can be started from the lockscreen. Is this possible(it seems to be posssible, since i see apps like this on the Google Playstore) and how would i achieve this?

You might be better off replacing the lock screen. You'll have more control and be able to provide a better user experience. Downside is you have a lot of code to write.
See this:
Creating an Android Lock Screen App.

Making a lock screen widget was possible in between android 4.4.2 until android lollipop. All other version do not have this ability. As such the best alternative would be for your app to replace the built in launcher and create its own lockscreen which you would be able to customize yourself.

Using the camera inside an Android app

I want to create an Android app which uses a camera, but I don't want the app to redirect to the default camera app on the device.
I want a custom-made camera app specifically for the app. How do I implement it?

Here is a nice tutorial to accomplish it.
Camera Integration with Surface View
You can make your custom changes on the SurfaceView according to your requirements.

Look into this tutorial http://www.airpair.com/android/android-camera-surface-view-fragment
Link 2
you can use SurfaceView Fragment.

I used https://github.com/commonsguy/cwac-camera to get custom camera done.
The library #commonsware made, great library with great documentation and support.

Working with java media framework in Android

Is it possible to use JMF in Android? JMF has good functionality?
I'm basically trying to create a video in my android app. So any other ideas for creating the video are welcome.
Thank you.

JMF will not work in Android.use MediaPlayer API instead.
Media and Camera

Xuggler doesn't work on android...
You should compile and use FFMEP, like in this tutorial :
FFMEP tutorial

Fingertip drawing applications on Android?

I'm a new user to this interesting forum!
I want start developing an application for android and before starting i want learn about some android features...
The first android feature is how to correlate finger motion on the screen with java...
Are there any source code examples that show how to draw with your finger on an android screen?
Can you suggest a good place for me to download an example?
thanks

The ApiDemos that come with the SDK have an example called TouchPaint that does exactly this... it's a simple little finger drawing app. The source is actually very easy to read and it shows all of the basics.

Check out this tutorial on drawing with a canvas in Android. There are some source code examples there for you as well.
Also, the Android developer's guide and tutorials on the Google site are great. That's what I started with.