One TTS job with sentence segments vs one job per sentence

If you need a voiceover as separate sentence files, make one Sume TTS job with timestamps: {words: true} and segmentation: {mode: "sentence"} instead of one job per sentence. The character price is the same, $0.0475 per 1,000, but one job means one idempotency key, one poll and one result. The result returns gapless segments[] and, for wav or raw output, a sample-exact audio_url for each (API reference).

What the single job gives you

• Gapless segments: segments[i].end equals segments[i+1].start.
• A cut that follows the last word of each sentence by boundary_lead_ms, 70 ms by default, in a range of 0 to 500. The next segment absorbs the pause.
• Slices only for wav and raw. With mp3 you get timings without per-segment audio_url.
• emit_audio defaults to true, so request wav and you get the slices.

{
  "transcript": "Hook line. Offer line. Call to action.",
  "avatar_handle": "your-voice-handle",
  "output_format": {"container": "wav", "encoding": "pcm_s16le", "sample_rate": 44100},
  "timestamps": {"words": true},
  "segmentation": {"mode": "sentence", "boundary_lead_ms": 70}
}

The case for separate jobs

One job per sentence is still right when you want to redo a line without touching the rest. A change in one sentence of a single job means a new job for the whole script. At 1,000 characters that is $0.0475, so the extra cost of a full redo is small, and the new take may differ in delivery from the earlier one. Per-line jobs keep the untouched sentences exactly as they were.

Compare the two

The trend behind it

Streaming speech is the headline: Microsoft quotes MAI-Voice-2.1-Flash at 150 ms end to end for 45 seconds of audio (Microsoft AI, read 2026-10-04). If you want sentence-level control from a job API, segmentation is the equivalent. Poll the job as the jobs docs describe and read segments[] when the result is ready.

Rule of thumb: use one job with segments for a script that is read in order, and per-sentence jobs for lines that are edited and swapped on their own.