Change External Subtitle Position on Exoplayer

Most subtitle formats can specify for each cue where in the viewport it should be drawn. The SubtitleView is transparent and exactly overlaid on the video viewport. The SubtitleView can position the cue text (or image) anywhere within itself, as specified by the positioning information from the subtitle source data.

In some cases, the position isn’t specified in the source data . This is usually indicated by Cue.DIMEN_UNSET values for Cue.line and/or Cue.position. In that case SubtitleView decides to draw the cue in a ‘default’ position, which is bottom-center. The SubtitleView#setBottomPaddingFraction() method can change the vertical position of these cues (and specifically only the cues with no explicit positioning info from the source data). There’s currently no way to configure the horizontal position of this ‘default’.

Do you want to position all cues in a fixed location, or only those that don’t carry their own positioning info?

You can achieve either by subclassing PlayerView and mutating the Cue objects in onCues() before passing them to super.onCues(). You’ll want to change the line and position fields (and possibly lineAnchor, lineType and positionAnchor too). If you only want to move ‘default positioned’ cues, then only change a field if it’s set to Cue.DIMEN_UNSET.

Thanks for the sample project - I think I know what’s going on.

The subtitles in the stream you provided are WebVTT and don’t explicitly set the size property (i.e. width for horizontal text). The WebVTT spec tells us to default to size=100% in this case (step 3 here: https://www.w3.org/TR/webvtt1/#processing-cue-settings).

Additionally the cues all have alignment=middle (i.e. centre the text inside the cue box).

So since you pass the Cue size straight through without modifying it, the cue box will always be spanning all the way to the right hand edge of the screen (because as you adjust position and positionAnchor, the size will be shrunk just enough to avoid going out-of-bounds (i.e. > 100%)).

And then since you also pass alignment straight through, you’re only able to position cues in the middle of a box that spans all the way to the right hand edge of the screen. This makes it impossible to ever get cues into the left hand portion of the screen.

You should be able to fix this by modifying either size or alignment or both. I was able to get cues showing up on the left with your sample app by passing Layout.Alignment.ALIGN_NORMAL instead of cues.get(0).textAlignment.