Audio to SRT Converter – Free Online Subtitle Generator (SRT, LRC, ASS)
Need to turn an audio file into proper subtitles in seconds? The UD Tools Audio to SRT Converter is a free, browser-based tool that listens to your audio with a real speech-to-text engine and instantly produces timed subtitle files in SRT, LRC, or ASS format — ready for YouTube, VLC, video editors, or karaoke apps.
No software to install, no learning curve, and no watermarks. Upload an audio file or pull the audio straight out of a video, and download a clean subtitle file when you're done.
Try the Audio to SRT Converter
Upload an audio file (or extract audio from a video) and download a ready-to-use SRT, LRC, or ASS subtitle in under a minute.
Open Audio to SRT Converter- What is an Audio to SRT Converter?
- How the UD Tools Converter Works
- How to Convert Audio to Subtitles (Step-by-Step)
- SRT vs LRC vs ASS: Which Format Should You Use?
- Understanding Subtitles and Transcription Accuracy
- Working With Video Content
- Practical Examples and Use Cases
- Common Mistakes and Quick Tips
- FAQ
What is an Audio to SRT Converter?
An audio to SRT converter is a tool that takes an audio file — like an MP3 recording, podcast episode, lecture, or song — and turns the spoken words inside it into a timed subtitle file. The output file (an SRT, LRC, or ASS) tells a video player exactly what text to show, and at what second, so captions stay in sync with the audio.
The UD Tools Audio to SRT Converter does this in three steps: it transcribes your audio with a real speech-to-text model, automatically time-stamps every sentence, and packages the result into the subtitle format you choose. You don't need a video editor, a paid subscription, or any technical setup — just an audio file and a free AssemblyAI API key.
How the UD Tools Converter Works
Under the hood, the tool is simple by design. It runs entirely in your browser and talks directly to AssemblyAI's speech recognition API:
- Upload: You pick an audio file (MP3, WAV, M4A, AAC, OGG, FLAC, WEBM) or a video file. If it's a video, the built-in extractor pulls the audio track out for you on the same page.
- Transcribe: The audio is securely uploaded to AssemblyAI and run through their Universal-2 speech model, which returns time-stamped text.
- Format and download: The result is converted into the subtitle format you selected — SRT, LRC, or ASS — and offered as a direct download.
You can also preview the full transcript on screen, copy it, or edit it before downloading. The original API key is stored only in your browser's local storage if you choose the "Remember" option — UD Tools does not keep a copy.
How to Convert Audio to Subtitles (Step-by-Step)
Follow these six steps to go from a raw audio file to a finished, time-synced subtitle file.
- Get a free AssemblyAI API key. Sign up at assemblyai.com and copy your API key from the dashboard. The free tier includes up to 100 hours of transcription per month and does not require a credit card.
- Open the UD Tools converter and paste your key. Go to the Audio to SRT Converter page and paste the API key into the field. Optionally enable Remember my API key to save it locally for next time.
- Upload your audio (or video) file. Drag and drop the file or click Browse. An in-page audio player appears so you can confirm the file before converting. If you only have a video, the same page will extract the audio for you.
- Click "Convert to Subtitles". A progress bar shows the upload and transcription status. Most files under 10 minutes finish in 30 to 90 seconds.
- Review the transcript. The full text appears on screen with timestamps. You can read it, fix any obvious typos, and copy it for reuse in show notes, blog posts, or social media.
- Download your subtitle file. Choose SRT for YouTube and most editors, LRC for music and karaoke, or ASS for advanced styling. The file downloads instantly and is ready to use.
SRT vs LRC vs ASS: Which Format Should You Use?
All three formats store time-stamped text, but they were built for different use cases. Pick the one that matches where your subtitles will play.
| Format | Best for | Styling | Player support |
|---|---|---|---|
| SRT (SubRip) | YouTube, Vimeo, Facebook, VLC, Premiere, DaVinci Resolve | Plain text only | Widest support — works almost everywhere |
| LRC (Lyrics) | Music players, karaoke apps, YouTube Music-style lyric videos | Basic line-by-line, some players support word-level timing | Music-focused players and lyric apps |
| ASS (Advanced SubStation Alpha) | Anime fansubs, stylized captions, advanced editors | Custom fonts, colors, positioning, effects | VLC, Aegisub, OBS, some video editors |
Understanding Subtitles and Transcription Accuracy
What Is an SRT File?
SRT (SubRip Subtitle) is the most widely used subtitle format. It contains numbered blocks of text, each with a start and end timestamp, which video players use to display captions in sync with the audio or video. If your subtitles are for a video project, you can extract the audio directly from that video using the built-in extractor on the same page before generating your SRT file.
How Accurate Is the Transcription?
The UD Tools Audio to SRT Converter uses AssemblyAI's Universal-2 speech recognition model, which delivers high accuracy for clear audio. Accuracy can drop with background noise, multiple overlapping speakers, or heavy accents — that's why the page shows the full transcript before download so you can review and tweak anything that looks off.
What Affects Subtitle Quality?
- Audio clarity: Clean, single-speaker recordings produce the most accurate subtitles.
- Background noise: Music, crowd noise, or echo can confuse the speech model.
- Speaker count: The model handles multiple speakers, but heavy crosstalk reduces accuracy.
- Accent and language: Universal-2 supports many languages and accents well; very strong regional accents may need a quick manual pass.
Working With Video Content
Many creators start with a video file rather than standalone audio — a YouTube upload, a recorded lecture, or a podcast episode filmed on camera. Instead of hunting for a separate converter, the UD Tools page includes its own audio extraction step, so the whole process, from video to finished SRT file, happens on the same page without juggling multiple tools.
You drop in the video, the page pulls out the audio track, and the transcript is generated from that. No re-uploading, no second tool, no wasted bandwidth.
Practical Examples and Use Cases
The same converter works for very different kinds of creators. A few real scenarios where it saves the most time:
- YouTube creators: Drop a finished video's audio track in, get an SRT, and upload it as captions to improve watch time, SEO, and accessibility.
- Podcasters: Convert each episode's audio into a transcript you can repurpose as a blog post, newsletter, or social thread.
- Online course creators: Auto-generate captions for lectures so students can follow along, search inside the video, or watch muted on the go.
- Musicians and lyricists: Generate an LRC file for karaoke-style lyric videos or for music players that support synced lyrics.
- Journalists and researchers: Turn interview audio into a searchable text document in minutes.
- Educators and trainers: Caption recorded lessons and make them accessible to students who are deaf or hard of hearing.
Common Mistakes and Quick Tips
- Skipping the transcript review. Even good speech-to-text makes occasional mistakes — always skim the transcript before downloading the SRT.
- Uploading a huge uncompressed file. 20 MB is the limit. Compress to MP3 or M4A first if your recording is larger.
- Using the wrong subtitle format. Music and karaoke need LRC; most video platforms need SRT; stylized fan captions need ASS.
- Forgetting to check the API key. If the conversion fails immediately, the API key is the first thing to verify.
- Ignoring background noise. Heavy noise or music under the voice will reduce accuracy. Use the cleanest recording you have.
Frequently Asked Questions
What is an SRT file and what is it used for?
An SRT (SubRip Subtitle) file is a plain text subtitle format that contains numbered caption blocks, each with a start and end timestamp. Video players like VLC, YouTube, and most editors use SRT files to display captions in sync with the audio or video.
Can I convert MP3 to SRT for free?
Yes. The UD Tools Audio to SRT Converter accepts MP3, WAV, M4A, AAC, OGG, FLAC, and WEBM, and generates a properly timed SRT file you can download in seconds. The tool itself is free; you only need a free AssemblyAI API key for transcription.
Do I need to install any software to use the converter?
No. The converter runs entirely in your browser. You upload the audio (or extract it from a video), the file is sent to AssemblyAI for transcription, and the resulting SRT, LRC, or ASS file is generated and downloaded from the same page.
What is the difference between SRT, LRC, and ASS files?
SRT is the standard subtitle format for video platforms and editors. LRC is used by music players and karaoke apps to display scrolling, time-synced lyrics. ASS is an advanced subtitle format that supports custom fonts, colors, and positioning for stylized captions.
How accurate is the audio-to-subtitle transcription?
The tool uses AssemblyAI's Universal-2 speech recognition model, which delivers high accuracy for clear single-speaker audio. Accuracy drops with heavy background noise, strong accents, or multiple overlapping speakers, so reviewing the transcript before downloading is recommended.
Can I use this tool if I only have a video file?
Yes. The same page includes a built-in audio extractor. You can pull the audio track out of any supported video, then send it straight into the converter without downloading or re-uploading anything.
Is my API key and audio file safe?
Your AssemblyAI API key is stored only in your browser's local storage if you enable the Remember option, and your audio is uploaded directly to AssemblyAI over HTTPS for transcription. Nothing is stored on UD Tools' servers.
What is the maximum audio file size I can convert?
The converter supports audio files up to 20 MB. For longer recordings, split the file or upgrade your AssemblyAI plan for higher per-upload limits.
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Open the UD Tools Audio to SRT Converter and turn any audio file into a properly timed SRT, LRC, or ASS subtitle — free, in your browser, in under a minute.
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