WEBVTT
NOTE
Background for Voice1 should apply.
The other two backgrounds should not render because non-data URLs are not supported.
STYLE
::cue(v[voice=Voice1])
{
    background: url(data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7)
}
::cue(b)
{
    background: url("support/background.png")
}
::cue(i) {
    background: url("support/background.png");
    background: -webkit-image-set(url("support/background.png") 1x, url("support/background.png") 2x);
}
00:00:00.000 --> 00:00:05.000
<v Voice1>This <i>is</i> a <b>test</b> subtitle
00:00:00.000 --> 00:00:05.000
<v Voice2>Here <i>is</i> a <b>second</b> subtitle
