Guide: How to use AI to create a multilingual voiceover

The rise of AI voiceover is transforming how businesses localise their audiovisual content. It promises faster turnaround times, reduced costs and easy scalability. However, while the technology is impressive, utilising it to achieve the best quality results requires expertise. 

At Comtec, we’re excited to launch our new AI voiceover service, designed to help brands harness this emerging technology without compromising quality. To test it, we used one of our own webinars featuring James, our Head of Commercial, as the source material and created a Spanish version, complete with a natural-sounding, well-synced AI voiceover. 

We like to call him “Spanish James.” If you’d like to see what it looks like, here’s a sneak peek:

While, in many instances AI can deliver results at the touch of a button, this wasn’t as straightforward as you might think.

Here’s a roundup of what we learned and what content teams exploring AI voiceover need to know.

Many people assume AI voiceover is as simple as pressing a button. 

However, to do it well – and produce something your audience will actually want to watch – requires time, tools, and a lot of human expertise.

Here’s how our process worked:

1. Transcription and script prep

We started by transcribing the English audio using our AI voiceover platform. This required a detailed human QA to correct filler words, punctuation, and misheard phrases – issues that AI transcription tools still struggle with.

2. Machine translation and post-editing

Once we had a clean transcript, we utilised AI translation tools to create a first draft in Spanish. However, because the source content was creative and informal, our linguists spent over 20 hours post-editing it to ensure the tone, clarity, and flow were suitable for the Spanish audience.

3. Voice generation and linguistic QA

This is where the magic—and the challenges—of AI voiceovers truly come into play. We uploaded the final script into our AI voiceover tool, selected Spanish voices that best matched the original speakers, and generated the AI voiceover. Then came the detailed editing: shortening sentences to avoid overlap, correcting the pronunciation of acronyms and names, and adjusting the pacing to match the visuals.

Our AI voiceover platform has a voice library that lets you choose an AI voice based on gender, age and voice timbre, so you can try to closely match the AI voiceover to the original speaker.

4. Audio-video synchronisation

It’s not enough for the audio to sound natural; it also has to fit the on-screen action. We ensured that the timing was correct, the right speaker was assigned, and the rhythm matched the original video as closely as possible for a fully synchronised, localised experience.

5. Final QA and export

Finally, we exported the localised video and then conducted a final round of quality assurance (QA) before signing it off.

At the heart of a successful AI voiceover project isn’t just a clever algorithm; it’s an experienced linguist who understands how to shape the output into something natural, polished and culturally appropriate.

Silvia, one of our trusted and long-standing linguists, handled the post-editing and voiceover QA for our Spanish version of the webinar. 

Her role was absolutely critical. The AI translation alone was nowhere near ready for use: although it provided a solid draft, it struggled with tone, pacing, terminology and structure. 

Here’s where her expert input made all the difference:

1. Rewriting for clarity and fluency

AI translation tools often produce literal or awkward phrasing. Silvia reworked the copy to sound natural and authentic, which is especially important for a spoken format, where tone and flow matter as much as the meaning itself. She also adjusted the structure to suit spoken delivery, breaking up long or flat sentences and ensuring the rhythm worked well in Spanish.

2. Fixing pronunciation issues

The AI voiceover tool mispronounced key content, including acronyms, numbers, company names, and English terms. For example, “p.ej.” was read out phonetically rather than “por ejemplo”. Silvia had to manually rewrite or tag these items so the AI could generate the correct pronunciation, a fiddly but vital step that ensured the final voiceover didn’t sound clunky or confused.

3. Timing and alignment

One of the most challenging aspects of the project was matching the Spanish audio to the original English video. Translations are rarely the same length, and voiceover tools can only do so much to automate this process. Silvia shortened strings, rephrased content, and adjusted speech tempo to avoid overlapping dialogue or unnatural pauses – all while preserving the meaning and keeping the content engaging.

4. Real-time fine-tuning

Using our AI voiceover platform, Silvia could test each edit immediately against the video, listening live to how the voiceover fit. This real-time feedback loop enabled her to refine pronunciation, pacing, and tone line by line, resulting in a final product that felt smooth and polished.

Our AI platform lets you finetune the translation so the new audio fits the visual of the speaker. It makes the end product as natural-looking and sounding as possible.

5. Strategic judgement
Beyond the technical tasks, Silvia brought cultural intelligence and content judgement to the table. She knew when to prioritise fluency over literal translation, when to preserve our brand tone, and how to adapt to the expectations of a Spanish-speaking audience. This level of decision-making is something AI simply can’t replicate.

So, was it worth it? Did we save time and/or money?

In a word: Absolutely. 

Using AI voiceover cut the total cost of localisation by around a third and shaved 4–5 days off the delivery time compared to using human voiceover.

For this type of internal or marketing content, where fast turnaround and budget efficiency are key, the advantages are clear.

When does it make the most sense to use AI voiceover?

AI voiceover is not a replacement for professional voice actors, particularly when nuance, emotion or brand tone are paramount. 

But for specific content types, it’s a brilliant addition to your localisation toolkit:

• Marketing videos – product explainers, launch videos, campaign assets, social media
• Training and eLearning – especially when content needs to be updated frequently
• Internal comms – to engage multilingual teams at speed

As tempting as it may be to attempt an AI voiceover yourself, without the correct workflow, linguistic insight, and technical oversight, you risk producing poor-quality outputs that may alienate or confuse your audience. And with the time it would take to set it up, overlay the audio, correct the dialogue etc., you might even spend more time on it.

From a viewer’s perspective, mistranslations, awkward timing, robotic delivery and mispronounced names can quickly undermine the professionalism of your content. Your audience may tune out your content or, worse, laugh for the wrong reasons.

At Comtec, we combine powerful AI tools with expert human linguists and project managers. That’s what turns raw technology into professional-quality content that connects with your audience, and often for much less than you’d think.

Would you like to discuss a project and receive a quick quote? Get in touch; we’d love to help!