Synthesia works well -- until it doesn't. And when something breaks, the error messages aren't always helpful. "Generation failed" is not a fix. "Rendering error" doesn't tell you what to try next.
I've run into most of these problems personally, and I've tracked down the practical causes and fixes. The issues below cover the majority of what people actually run into with Synthesia.
New to Synthesia and just trying to get started? Read the how to use Synthesia guide first. This article assumes you know what you're trying to do -- you just can't get it done.
1. Video Generation Stuck or Failing
You click Generate, a progress bar appears, and then it just... sits there. Or it fails with a vague error after a few minutes.
This is the most common complaint, and there are a few likely causes:
Try a hard refresh first. Ctrl+Shift+R on Windows/Linux, Cmd+Shift+R on Mac. Not regular F5 -- a hard refresh clears the cached state and re-establishes your session with Synthesia's servers. If your connection got stale during generation, this often resolves it and shows you the actual video status.
Switch browsers. Try Chrome if you're on Firefox or Edge, or vice versa. Synthesia communicates with your browser in real time during generation. Browser extensions, especially ad blockers or privacy tools, sometimes interfere with this connection. Testing in a fresh browser window rules it out fast.
Check Synthesia's status page. Like any cloud video platform, Synthesia has occasional server-side failures and maintenance windows. If your videos are consistently failing across multiple attempts, check their current service status. If it's a platform issue, waiting is the only option.
Video length. Longer videos have higher failure rates. If your script is very long and generation keeps failing, try splitting the project into shorter segments -- under 5 minutes per video is a good target.
Check whether your credit was consumed. If a generation fails, Synthesia should restore the credit. This doesn't always happen automatically. If a credit went missing on a failed generation, contact support -- they'll restore it.
2. Avatar Looks Robotic or Unnatural
The video generated fine technically. But the avatar's delivery feels stilted -- speaking too fast, clipping between phrases, or just "off" in a way you can't exactly explain.
Almost always a script issue, not an avatar issue.
Punctuation controls pacing. The avatar's speech rhythm is determined entirely by your script's punctuation. Commas create short pauses. Periods create longer pauses. Ellipses (...) create the longest pauses. A script written like a document -- long sentences, minimal punctuation -- will be delivered like a machine reading a legal filing. Write it like you'd actually speak it.
Break up long sentences. This is the single biggest cause of robotic avatar delivery. Any sentence over 20-25 words should become two sentences. Not for grammar -- for how it sounds when spoken. Read your script aloud before you submit it. Anywhere you naturally pause or take a breath, add punctuation.
Acronyms and unusual terms get mispronounced. "SQL" might come out as "S-Q-L" instead of "sequel." Your product name might get mangled. Any technical term, brand name, or unusual word is worth checking in preview. Write the phonetic pronunciation if you need to: "MySQL (my sequel)" or just rewrite to "my-sequel" in the script itself.
Try a different avatar. Not all avatars are equal in expressiveness. Some have more natural head movement and expression variation than others. If a particular avatar consistently feels off, try another. Premium or newer avatars are generally more natural.
3. Audio Sync Problems
The avatar's mouth movements don't match the audio -- the lip sync is clearly off.
This is typically a rendering issue, not a permanent problem. If you're watching a freshly generated video and the sync looks wrong, try regenerating the video. Occasionally a generation run will have sync degradation, especially for longer scenes. Regenerating usually produces a correct result.
Watch for this particularly at the start and end of scenes. Lip sync errors tend to cluster at scene boundaries -- the first word of a scene or the last word before a cut. If the rest of the scene looks fine but the edges are off, regenerating the affected scene (not the whole video) is the fix.
Very fast delivery creates sync issues. If your script has run-on sentences and the avatar is speaking rapidly, the lip sync engine has a harder time keeping up. Slowing down the script by adding pauses and splitting sentences reduces sync errors.
Check your voice/avatar combination. Some voice-avatar pairings produce better sync than others. If you're consistently seeing sync problems with a specific combination, try a different voice with the same avatar and see if it improves.
4. Account and Login Issues
You can't log in, your activation email never arrived, or your account shows the wrong plan status.
Check spam and promotions folders first. Synthesia's activation and password reset emails routinely end up in spam or in Gmail's Promotions tab. Search your entire inbox for "synthesia" before trying anything else.
Wait before clicking "Resend." If you just signed up and nothing arrived: wait at least five minutes. Email delivery can be delayed, and clicking Resend repeatedly too quickly can trigger rate limiting. Wait, then try resend once.
Activation link expiration. Synthesia's email verification links expire after 24-48 hours. If you're trying to use an old email, the link won't work. Request a fresh verification email.
Clear browser cache for synthesia.io. Incomplete previous sessions can cause login conflicts. Clear cookies and cache for synthesia.io specifically, then attempt login fresh.
Corporate email blocking. Some corporate IT setups filter verification emails from unknown senders. If you signed up with a work email and nothing arrives, try a personal Gmail address. If you need your work email for SSO, involve your IT team.
Plan not reflecting correctly. If you upgraded your plan but the interface still shows the previous tier: hard refresh the dashboard (Ctrl+Shift+R). If that doesn't update it, log out completely and log back in. Payment processing can occasionally lag a few minutes before the platform recognizes the upgrade.
5. Export Failing or File Issues
The video generated fine, but the download is failing or the exported file won't work.
Use the direct download link. Synthesia provides both a hosted shareable link and a direct download option. If the download button is failing, try the shareable link approach -- it sometimes works when the direct download doesn't.
Check your connection. Large video files (a 5-minute 1080p video can be 200-400MB) will time out on slow or unstable connections. If your download keeps failing at a percentage: try pausing and resuming via your browser's download manager.
Check export settings. If your file is unexpectedly large, verify the export resolution. 4K exports are much larger than 1080p. For web distribution and social media, 1080p is the right setting.
The video may legitimately be large. A long video at high resolution will produce a large file. If file size is a constraint, either use Synthesia's shareable hosting link (no download required) or consider breaking the video into shorter segments.
Re-export from the project. If a downloaded file is corrupted or won't play: go back to the project, locate the completed video, and re-download. The server-side copy is usually intact even if the download had issues.
6. Browser Compatibility Problems
Synthesia acts strange, loads slowly, or some features don't appear in your browser.
Chrome is Synthesia's primary supported browser. Other browsers work, but Chrome tends to have the fewest compatibility issues. If you're experiencing interface problems in Firefox, Safari, or Edge, try Chrome first before troubleshooting further.
Disable browser extensions for testing. Ad blockers, privacy extensions (uBlock Origin, Privacy Badger), and VPN extensions can interfere with Synthesia's real-time video generation connection. Create a browser profile with no extensions, or use incognito/private mode which disables most extensions by default.
Clear cache and cookies. A cached old version of the Synthesia interface can cause display bugs, missing buttons, or incorrect feature availability. Clear cache specifically for synthesia.io and reload.
Check WebGL and JavaScript. Synthesia's editor uses WebGL for previews. In some corporate or restricted environments, WebGL is disabled. If the editor looks blank or certain features won't load, this could be the cause. Your IT team can confirm whether WebGL is blocked.
Try a fresh browser window after logging in. If you've had the Synthesia tab open for many hours, session tokens can expire. Opening a fresh window and logging in again resolves most session-related interface weirdness.
7. Credit and Quota Issues
You ran out of credits faster than expected, or you're seeing quota limit errors.
Credits scale with video length. A short video (under a minute) costs one credit. Longer videos cost more. The exact credit cost is visible before you click Generate -- check it before starting a long video if you're running low.
Regenerating costs credits. Every time you click Generate on a video, it consumes a credit (or partial credit). If you're iterating heavily on a script and regenerating multiple times, those credits add up. Get your script as close to final as possible in preview before generating.
Failed generations should refund credits. Synthesia's policy is to restore credits for generation failures. If a credit was consumed on a failed generation, check your credit balance and contact support if needed. This doesn't always happen automatically.
Starter plan limits are strict. The $29/month Starter plan includes 10 credits per month. If you're hitting that ceiling regularly, the math on upgrading to Creator is worth doing -- unlimited generation at $89/month makes sense if you're producing more than 10 videos per month.
Custom avatar generation counts against quotas. Creating or refreshing a custom avatar from your own footage uses credits. These don't just cost credits at setup -- regenerating a custom avatar (for example, to add a new phrase) uses additional credits.
If Synthesia's support is needed, they're reachable via the in-app chat widget. Response times are generally reasonable for paid plan subscribers.
Most Synthesia problems have straightforward fixes. The platform is solid for AI avatar video production -- but cloud video rendering has inherent edge cases, and knowing what to try first saves a lot of frustration.
For help getting started with Synthesia's full feature set, see our how to use Synthesia guide. For how Synthesia compares with other AI video tools, see our best AI video generators roundup. And if you're evaluating HeyGen as an alternative, our HeyGen troubleshooting guide covers that platform's common issues.
Disclosure: TechSifted does not currently have an affiliate relationship with Synthesia. Links to Synthesia in this article are direct, non-affiliate links -- we earn nothing if you sign up. Synthesia is on our affiliate application list for March 19, 2026. This article was written before any affiliate relationship exists and reflects our honest assessment.
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