Pause between narration lines: TTS pause markers or audio concat?

Put the pause where the audio is made, not where it is joined. Deepgram's Flux TTS supports pause markers of 500 to 3000 ms, but Sume's timeline audio concat joins clips sample by sample with no silence added at the seams, so a gap between two separately generated lines has to already exist inside one of the clips.

What Deepgram's pause markers allow

The Deepgram changelog entry dated September 30 describes pause markers in Flux TTS with fixed limits, plus inline IPA pronunciation and a cap on speed when pauses are used.

What the Sume concat does at a seam

Sume's timeline audio job with operation: "concat" takes 1 to 20 ordered parts and returns one gapless file. The docs describe the join as sample-domain with no re-synthesis and no silence at the seams. The result includes segments[] with index, start and duration_seconds, which are the offsets you use to re-base video starts. The job costs $0.01 flat and the default output is sample-exact wav.

The consequence is simple: two lines concatenated will play back to back. If you want a beat between them, generate it in the line, for example with a vendor pause marker.

Choosing where to pause

• Short beats inside a sentence or between two sentences of one line: use the pause markers your TTS supports, within its per-request cap.
• Many lines in one scene: keep each line a separate clip so you can re-time a single line, then concat once and read segments[] for the offsets.
• More than 8 pauses in a read: split the text across requests so that each stays under the cap.

A concat request with trimmed edges

A part can carry source_in and duration, which lets you trim breath or tail from a line before the join. Trimming is the opposite of padding: it tightens the rhythm. Preview the result, then adjust.

curl -X POST https://api.sume.com/v1/timeline-1.0/audio \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: narration-concat-001" \
  -d '{
    "operation": "concat",
    "parts": [
      { "url": "https://media.sume.com/artifacts/artf_demo/line1.wav" },
      { "url": "https://media.sume.com/artifacts/artf_demo/line2.wav", "source_in": 0.1, "duration": 1.8 }
    ]
  }'