Do captions help the TikTok algorithm?
Yes — indirectly. Captions raise watch-time and completion rate, both of which feed TikTok's For You ranking. They also help TikTok's content classifier index your video correctly.
Detail
TikTok doesn't publicly weigh captions as a direct ranking signal, but two indirect effects are well-documented. First, captioned videos retain ~30% more watch-time on muted feeds (which is most of TikTok). Higher watch-time directly feeds the For You ranking. Second, TikTok's content classification system uses ASR on uploaded videos to understand topic — uploading or burning in clean captions disambiguates your topic for the classifier and improves topical recommendation accuracy. Net effect: captions are a free, large lift on TikTok performance.
56–72px on a 1080×1920 canvas — about 6–8% of frame width. Use heavier fonts at the smaller end of the range and thinner fonts at the larger end.
Yes. YouTube indexes uploaded SRT/VTT transcripts in its search index. A clean transcript lifts discoverability 20–30% over auto-captions.