Most AI music tools hand you whatever length the model decides. That is fine for a demo, but real projects need a runtime: a 15-second ad, a 2-minute vlog bed, a 6-minute focus loop. A good AI music generator lets you set song duration on purpose. Here is how to set custom length on GenMusicLab and how to pick the right duration.
How to set a custom length
1. Open the generator Go to the AI Music Generator and start a track with a prompt, or attach an image, video, or audio as your reference.
2. Set the duration In the form, choose a preset or enter a custom value from 10 to 360 seconds. Out-of-range values snap to the nearest limit (5 becomes 10, 400 becomes 360).
3. Or pick Auto Not sure how long the idea wants to be? Choose Auto and let the model decide, then trim or regenerate if you need a fixed runtime.
4. Generate and check The track comes back at your chosen length. Preview, keep the take you like, and download it royalty-free.
Which length fits which job
- 10 to 30 seconds: product ads, YouTube intros, TikTok and Shorts beds, stingers.
- 60 to 120 seconds: vlogs, explainer videos, social promos, gameplay loops.
- 180 to 360 seconds: lofi focus sessions, ambient background, full songs, long-form ambience.
Matching the runtime to the job saves you from trimming a 3-minute track down to a 15-second ad — or stretching a jingle across a 10-minute video.
Tips for cleaner results
- Decide the length before you prompt. A 15-second clip and a 3-minute song want different structure, so tell the generator first.
- Use loops for background. For focus or ambience, longer tracks with a smooth feel work better than short ones on repeat.
- Pair length with input mode. If you score a video, set the duration close to the clip. If you hum a melody, let Auto find the natural length, then adjust.
- Trim after, if needed. Download the file and cut it in your editor for a precise ending.
Why custom length matters
Stock libraries force your edit to fit their tracks. A generator with real length control flips that: the music is built to your runtime. For creators who publish regularly, that difference is the gap between "good enough" and "fits exactly."
You can also turn a photo into a song or guide a track from a reference clip using the same length controls.
FAQ
Q: Can I set a custom song length in an AI music generator? A: Yes. GenMusicLab lets you pick a preset or enter a custom duration from 10 to 360 seconds. You can also choose Auto and let the model decide the length.
Q: What is the shortest and longest track I can make? A: The custom range is 10 to 360 seconds. Values outside that range snap to the nearest allowed limit, so a 5-second request becomes 10 seconds and a 400-second request becomes 360.
Q: When should I use a short track versus a long one? A: Short tracks (10 to 30 seconds) suit ads, intros, and shorts. Mid tracks (60 to 120 seconds) suit vlogs and explainers. Long tracks (180 to 360 seconds) suit ambience, focus sessions, and full songs.
Q: What does Auto duration do? A: Auto lets the model choose a length that fits the musical idea. Use it when you care more about the arrangement than a fixed runtime.
Q: Is the music still royalty-free at any length? A: Yes. Tracks generated at any duration on GenMusicLab are royalty-free and cleared for YouTube, social media, podcasts, ads, and client work.