Video boot intro

[schmurtzm]

Related to this discussion : #1325
Note that it would impact the boot time of course but if it optional why not.
A simple use of ffplay could come just after init_system function

echo 0 > "/sys/module/gpio_keys_polled/parameters/button_enable"
LD_PRELOAD=$miyoodir/lib/libpadsp.so $sysdir/bin/ffplay -autoexit -vf "hflip,vflip" -i -nostats  $sysdir/boot.mp4
echo 1 > "/sys/module/gpio_keys_polled/parameters/button_enable"

We could run it even before audioserver but it would triggers a second pop sound at boot :

/customer/app/tinymix set 6 70    # avoid too loud sound
echo 0 > "/sys/module/gpio_keys_polled/parameters/button_enable"
$sysdir/bin/ffplay -autoexit -vf "hflip,vflip" -i -nostats  $sysdir/boot.mp4
echo 1 > "/sys/module/gpio_keys_polled/parameters/button_enable"

Note that we disable the controls during the boot video.
Optimizing the video encoding is a good idea for example : h264,640x480, mono sound, mp3 128mbps

It could be nice to load some Onion components in background during the boot video (time sync for example but it would require to disable the UI (bootScreen binary) if the video is still playing. Also the video could replace the Onion splash.

May be we don't need any Tweaks app new option : the video is launched only if the file exist.