[Feature Request] Option to disable automatic speech speedup / time-stretching in Text-to-Speech

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
csharp
Domain
audio-video-rtc, desktop

Research direction

Start by locating the Text-to-Speech window and the code that fits generated speech to subtitle block duration. Trace how that code calls the TTS engine and applies time-stretching, then identify where a setting can control that behavior. Done means the setting preserves natural 1.0x playback when disabled; the optional subtitle end-time adjustment is not required by the request.

Written by the indexing model from the issue text.

Description

Is your feature request related to a problem? Please describe.
When generating audio using the Text to Speech feature, Subtitle Edit automatically speeds up / time-stretches the generated speech if the target text exceeds the duration of the subtitle block.

While this keeps audio synced when embedding it directly with video, it creates a major issue when exporting/converting to standalone WAV audio files:

  1. The speedup results in unnatural, overly fast, or distorted speech.
  2. When generating a standalone WAV file (rather than hardcoding/multiplexing audio with video), forced time synchronization is often unnecessary. The speed adjustments defeat the primary purpose of generating a clean, natural-sounding audio track.

Describe the solution you'd like
It would be great to have an option (e.g., a checkbox or toggle in the Text-to-Speech window) to disable automatic speech acceleration / time-stretching.

If this option is disabled:

  • The TTS engine generates audio at its natural 1.0x playback speed regardless of the subtitle duration bounds.
  • (Optional) Subtitle line end-times could automatically extend to match the full length of the generated speech block when exporting.

Describe alternatives you've considered
Currently, the only workaround is manually extending every subtitle duration on the waveform before running TTS, or heavily trimming translated text to avoid triggering the speedup algorithm.

Additional context
When the goal is simply to export a WAV audio file from the subtitles, natural speech flow and voice quality are far more important than forcing the audio duration to fit strict timecode limits.

Dominant language
C#
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