Move burned captions: design.placement.anchor_ratio on Sume

Send design: {"placement": {"anchor_ratio": 0.6}} with a caption request to put the center of the caption line at 60 percent of the frame height from the top. The Sume captions docs list anchor_ratio and landscape_anchor_ratio as the placement fields, defined as the center of the line as a fraction of frame height. The punch and tiktok-green styles do not support design, so use one of the other styles if you need to move text.

Defaults by style

The accepted range is 0.05 to 0.95 and the defaults are from the caption renderer source in the Sume repository, not from the docs page. Treat them as values that can change.

Steps

• Find where your platform draws its own buttons, captions or labels on a vertical frame. Take that from the platform, since Sume does not know it.
• Grab a still with video_frames or video_inspect and mark the clear band.
• Add design.placement.anchor_ratio to the caption body. Values outside the range get a 400 at request time, so a bad number does not cost a render.
• Restyle with source_caption_id instead of video_url to try another ratio without a second transcription. The docs say the price does not change.
• Look at the result frame and adjust.

A lower ratio moves the line up, since the ratio counts from the top. Moving up from 0.74 to 0.6 lifts the line by 14 percent of frame height, which is about 269 pixels on a 1920-pixel-tall vertical.

Landscape and vertical

anchor_ratio is for portrait frames. For landscape frames use landscape_anchor_ratio, which is the same idea for a wide picture. Both are fractions of frame height measured from the top. If you send a vertical clip you only need the first.

Change one thing at a time. If you also change the style, the font, or the phrasing, you cannot tell which change moved the text. The design object merges over the style, so a request with only placement keeps every other style value.

Keep a note of the ratio that worked for each platform and style, so the next batch starts from a known value instead of a guess.

Budget and detail

To work out a ratio from a pixel position, divide the pixel height of the line centre by the frame height. A line centred 1300 pixels from the top of a 1920-pixel frame is 1300 / 1920, or about 0.677. Round to two decimals and send 0.68. Check the range, 0.05 to 0.95, before you send, since a value outside it returns a 400 at request time rather than a bad render.

What Sume does not do

Sume does not carry platform safe-zone maps, and it does not move captions automatically when a label appears. The number is yours to choose.