Runway sound effects API: 1 credit a second, 2 if you skip duration

Runway's sound-effects model, eleven_text_to_sound_v2, is priced at 1 credit per second of audio when you pass a duration and a flat 2 credits when you do not, with credits at $0.01 each. A 4-second effect with a duration is $0.04; the same effect with no duration is $0.02, which makes leaving the field out the cheaper choice for very short sounds.

Sume has no sound-effects model, so this page also lists what to do on Sume when a clip needs sound.

How is Runway's sound-effects call priced?

The pricing page has two rows for the model. With a provided duration the charge is 1 credit per second of audio. With no duration it is 2 credits. The API reference lists the request fields as model and promptText, both required, plus duration and an optional loop flag. Credits are sold at $0.01 in the developer portal.

The break-even is simple: with duration, a clip of exactly 2 seconds costs the same as the no-duration price, anything shorter is cheaper with duration, and anything longer is cheaper without it. The pages do not say how long a no-duration clip runs or what the model's maximum duration is, so check an output before you rely on that trick.

What does loop change?

The reference lists loop as an optional boolean for the sound-effect request, which asks for an effect that repeats cleanly. The excerpt does not state a price change for looping, and the pricing rows name only the duration case, so treat loop as included in the same per-second or flat charge until a test shows otherwise.

Looping matters for ambience beds: rain, a room tone or a machine hum that has to run under a long clip. Without it, you place a single effect repeatedly and listen for the seam.

What does Sume offer for effects?

Sume does not list a sound-effects model. Sound comes from three places: a video model that generates audio with the clip, where the create request takes generate_audio; the Music Router, which makes music and rejects a duration field; or your own effect files, placed on a Timeline with gain, fade-out and ducking.

If you need Runway-style standalone effect files, you can generate them elsewhere, import them, and mix them on the Sume Timeline. Imported media must be on Sume's media host before the timeline can use it. See the Timeline page for the soundtrack fields and refusal codes.

How should you budget a library of effects?

Decide first whether effects are standalone files or part of shots. For standalone files, count clips, multiply by seconds, and add 20 to 30 percent for regeneration, since you will discard some. For effects inside shots, the cost is part of the video charge and follows the model's resolution and duration, not a separate line.

• Short UI sounds under 2 seconds: Runway's no-duration price of 2 credits is the ceiling you pay.
• Ambient loops: set duration and loop, and budget by seconds.
• Sounds tied to one shot: write them into the video prompt on a Sume model that generates audio.
• Anything with a voice: use text to speech, not an effect model.

What should you test first?

Generate one clip each way on Runway, check the actual length of the no-duration output, and read the credits charged from your usage. Then do the same single-shot test on Sume with generate_audio on a model that supports it, and compare how well the written sounds match.

Cost is only half the choice. Sound that lands on a cut matters more than a cent saved, and that is easier to control with a file you place on the timeline than with a sound baked into a clip.