[WIP] Fix repaint bug in Gradio UI for audio generation

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Repaint from Gradio UI recreates entire song - does not respect repainting start and end seconds</issue_title>
<issue_description>Describe the bug
Repaint from Gradio UI recreates entire song - does not respect repainting start and end seconds

To Reproduce

1. Using the Gradio UI, select "Repaint"
2. load audio and load or type all the lyrics
3. leave caption blank
4. select a repainting start and end (~5 seconds)
5. click "generate music"

Expected behavior
Only the selected period should be replaced.
Instead, the entire song is regenerated/replaced.

Desktop (please complete the following information):

• OS: Windows 11
• Browser: Chrome 145.0.7632.76
• Commit 7004992

Additional context
I think this worked on the version I used ~2 weeks ago (after first release of Ace Step 1.5) but after an update a few days ago I found this problem.

• I have tried pt and vllm LM backend models and neither work
• I tried providing the entire lyrics and changing just the part I want to modify corresponding to the repaint start/end, and also just providing the lyrics for that period - neither method works
• I tried providing the original caption, or a caption that says I want to modify this part of the song - neither works

When I click generate and I look at the console, I don't see the start/end seconds logged anywhere, I wonder if they are actually being provided to the backend? Is there some way I can confirm the UI is providing the right inputs?
Is there a way I can work around this using the API directly? If so, does anyone have an example POST request I can make that gets the backend to repaint part of the audio?

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Repaint from Gradio UI recreates entire song - does not respect repainting start and end seconds #646

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