Document virtual display and "start app" features

PR #5370 <#5370>

README.md

@@ -31,6 +31,7 @@ It focuses on:
 Its features include:
  - [audio forwarding](doc/audio.md) (Android 11+)
  - [recording](doc/recording.md)
+ - [virtual display](doc/virtual_display.md)
  - mirroring with [Android device screen off](doc/device.md#turn-screen-off)
  - [copy-paste](doc/control.md#copy-paste) in both directions
  - [configurable quality](doc/video.md)
@@ -91,6 +92,12 @@ Here are just some common examples.
     scrcpy --video-codec=h265 -m1920 --max-fps=60 --no-audio -K  # short version
     ```
 
+ - Start VLC in a new virtual display (separate from the device display):
+
+    ```bash
+    scrcpy --new-display=1920x1080 --start-app=org.videolan.vlc
+    ```
+
  - Record the device camera in H.265 at 1920x1080 (and microphone) to an MP4
    file:
 
@@ -134,6 +141,7 @@ documented in the following pages:
  - [Device](doc/device.md)
  - [Window](doc/window.md)
  - [Recording](doc/recording.md)
+ - [Virtual display](doc/virtual_displays.md)
  - [Tunnels](doc/tunnels.md)
  - [OTG](doc/otg.md)
  - [Camera](doc/camera.md)

doc/device.md

@@ -78,3 +78,48 @@ By default, on start, the device is powered on. To prevent this behavior:
 ```bash
 scrcpy --no-power-on
 ```
+
+
+## Start Android app
+
+To list the Android apps installed on the device:
+
+```bash
+scrcpy --list-apps
+```
+
+An app, selected by its package name, can be launched on start:
+
+```
+scrcpy --start-app=org.mozilla.firefox
+```
+
+This feature can be used to run an app in a [virtual
+display](virtual_display.md):
+
+```
+scrcpy --new-display=1920x1080 --start-app=org.videolan.vlc
+```
+
+The app can be optionally forced-stop before being started, by adding a `+`
+prefix:
+
+```
+scrcpy --start-app=+org.mozilla.firefox
+```
+
+For convenience, it is also possible to select an app by its name, by adding a
+`?` prefix:
+
+```
+scrcpy --start-app=?firefox
+```
+
+But retrieving app names may take some time (sometimes several seconds), so
+passing the package name is recommended.
+
+The `+` and `?` prefixes can be combined (in that order):
+
+```
+scrcpy --start-app=+?firefox
+```

doc/virtual_display.md

@@ -0,0 +1,26 @@
+# Virtual display
+
+## New display
+
+To mirror a new virtual display instead of the device screen:
+
+```bash
+scrcpy --new-display=1920x1080
+scrcpy --new-display=1920x1080/420  # force 420 dpi
+scrcpy --new-display         # use the main display size and density
+scrcpy --new-display -m1920  # ... scaled to fit a max size of 1920
+scrcpy --new-display=/240    # use the main display size and 240 dpi
+```
+
+## Start app
+
+On some devices, a launcher is available in the virtual display.
+
+When no launcher is available, the virtual display is empty. In that case, you
+must [start an Android app](device.md#start-android-app).
+
+For example:
+
+```bash
+scrcpy --new-display=1920x1080 --start-app=org.videolan.vlc
+```