Podcast audio to a vertical video: cover stills plus a spine, $0.30

To turn an audio-only podcast file into a vertical video, use your cover art as still slots on Timeline 1.0 and the episode audio as the spine, then caption the result. A 59-second clip costs $0.10 for the render plus $0.20 for captions, $0.30 in all (read 2026-10-08). Stills are static holds, so the picture does not move, and the captions carry the motion.

How the program is built

Set audio.url to the imported episode file and audio.source_in to the second where your clip starts; the output length is still audio.duration_seconds. Then add stills as video[] slots. video[0].start must be 0, later starts must increase, and the last slot may end no more than 0.5 seconds before the spine ends. A still given a motion value is accepted but ignored, with a motion_ignored warning, which is a warning and not a failure.

Cost

The render reserves ceil(audio.duration_seconds / 60) minutes, so 59 seconds is one minute. Standalone captions are $0.20 for videos of up to 60 seconds; the audio must contain speech, because a silent clip fails with caption_no_speech.

The request

Three stills at about 20 seconds each keep the frame from feeling frozen. The body below uses a gentle fade between them. Run POST /v1/timeline-1.0/plan first if you want the billable minutes confirmed before spending.

curl -X POST https://api.sume.com/v1/timeline-1.0/render \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: ep42-audiogram-01" \
  -d '{
    "audio": { "url": "https://media.sume.com/artifacts/artf_demo/ep42.wav", "source_in": 812, "duration_seconds": 59 },
    "video": [
      { "source_url": "https://media.sume.com/artifacts/artf_demo/cover.png", "start": 0, "duration": 20 },
      { "source_url": "https://media.sume.com/artifacts/artf_demo/quote.png", "start": 20, "duration": 20,
        "transition": { "type": "fade", "duration": 0.5 } },
      { "source_url": "https://media.sume.com/artifacts/artf_demo/guest.png", "start": 40, "duration": 19,
        "transition": { "type": "fade", "duration": 0.5 } }
    ],
    "output": { "width": 1080, "height": 1920 }
  }'

Then caption

Pass the rendered MP4 URL to POST /v1/video-captions. Pick a style that keeps the words readable over a still: black-outline is the safe default for Hangul, and slam for Latin text. If the episode is not in English, hint it with language.