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[Feature Request] Precise positioning when exporting to Substation Alpha (ASS/SSA) #840
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Originally created by @yukichigai on GitHub (Aug 10, 2025).
The current method used for exporting SubStation Alpha format uses a combination of white space characters and line breaks to position caption text. However, both SSA and ASS are capable of far more precise positioning for text, both through Margin overrides and the "\posX,Y" manual placement tag.
The current WebVTT export includes more precise positioning information using the "line" tag, but player support for placement tags is spotty. Comparatively, SubStation Alpha is supported by far more software and devices. Using similar logic to what is present in the WebVTT export code it should be possible to add precise positioning information to SSA/ASS exported subtitles.
@sairajsachinpatil commented on GitHub (Jan 26, 2026):
PR #1885 appears to address the core feature request by adding guarded ASS/SSA \pos positioning for CEA-608 captions.
I also noticed the follow-up mention referencing #1108, so I wanted to check whether the current implementation fully covers the intended use cases. Please let us know if any further changes or validation are still expected.
@yukichigai commented on GitHub (Jan 26, 2026):
On first examination this doesn't seem to fully, no. My big concern is the "guarded" limitation to the lower third of the video area, as this may cause issues when captions are deliberately displayed at the top, e.g. to avoid overlapping with on-screen credits. I'll need to run some samples through it to check the output.
Regardless PR 1885 is a great change that I am glad to see.