Fixing Piper Text-to-Speech Issues With Incorrect Model JSON Downloads
Hey everyone, let's dive into an issue where Piper, a popular text-to-speech (TTS) engine, fails to work correctly due to incorrect download addresses for the model's JSON files. This article will break down the problem, its root cause, and how to fix it. This can impact usability, and correcting the problem helps maintain a smooth experience for all users. Understanding the technical details behind this issue ensures we can prevent similar problems in the future. This article serves to inform and guide users facing similar challenges.
Understanding the Issue
The core problem lies in how the JSON files for Piper's models are downloaded. Specifically, when using the Pied snap on Ubuntu 24.04, the downloaded JSON files contain errors, rendering them unusable. This issue manifests as a parsing error when Piper attempts to load the model, leading to the TTS engine's failure.
The Technical Breakdown
When installing the Pied snap on Ubuntu 24.04, the system places model files in the ~/snap/pied/common/models/ directory. For example, when installing the Czech voice model "cs_CZ Jirka medium," two files are created:
cs_CZ-jirka-medium.onnxcs_CZ-jirka-medium.onnx.json
However, attempting to use these files with Piper results in an error. The following command, typically extracted from ~/.config/speech-dispatcher/modules/piper.conf, demonstrates the failure:
~/snap/pied/common/piper/piper --model ~/snap/pied/common/models/cs_CZ-jirka-medium.onnx -s 0 --output_raw | aplay -t raw -c 1 -r 22050 -f S16_LE
This command produces the following error:
Playing raw data (...)
terminate called after throwing an instance of 'nlohmann::json_abi_v3_11_2::detail::parse_error'
what(): [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: '�'
This error indicates that the JSON file itself is malformed or contains invalid data. Let's dig into why this happens.
Root Cause: Incorrect JSON Content
The real culprit is the content of the cs_CZ-jirka-medium.onnx.json file. Instead of valid JSON, the file contains an error message:
✖ Invalid option: expected one of "true"|"1"|"yes"|"on"|"y"|"enabled"|"false"|"0"|"no"|"off"|"n"|"disabled"
→ at download
This error message suggests that the download process itself is the source of the problem. The file isn't being downloaded correctly, leading to this invalid content. This is a big deal, guys, because it means your TTS is dead on arrival.
The Erroneous Download Link
The issue stems from the download link used to fetch the JSON file. The link, found in places like VOICES.md on the Piper GitHub repository, looks like this:
https://huggingface.co/rhasspy/piper-voices/resolve/v1.0.0/cs/cs_CZ/jirka/medium/cs_CZ-jirka-medium.onnx.json?download=true.json
Notice the ?download=true.json at the end? That's the troublemaker! This extra .json extension in the GET attribute causes the download to fail, returning an error page instead of the actual JSON content. On the flip side, the ONNX file's download link, which looks like this:
https://huggingface.co/rhasspy/piper-voices/resolve/v1.0.0/cs/cs_CZ/jirka/medium/cs_CZ-jirka-medium.onnx?download=true
works perfectly fine. The key difference is the absence of the .json suffix in the download=true attribute.
The Fix: A Simple Change, A World of Difference
To fix this, all you need to do is replace the erroneous JSON file with one downloaded from the correct link. After obtaining a valid cs_CZ-jirka-medium.onnx.json file, Piper works as expected:
[2025-07-23 10:15:06.137] [piper] [info] Loaded voice in 0.243574008 second(s)
[2025-07-23 10:15:06.138] [piper] [info] Initialized piper
Ahoj
[2025-07-23 10:15:13.031] [piper] [info] Waiting for audio to finish playing...
[2025-07-23 10:15:13.031] [piper] [info] Real-time factor: 0.07763075986535904 (infer=0.042360694 sec, audio=0.5456689342403628 sec)
As you can see, the voice loads successfully, and Piper is ready to speak. The log output confirms that the voice model was loaded without issues. So, a small tweak in the download process can save the day.
Addressing the Problem: Piper vs. Pied
The million-dollar question now is: Who's responsible for this mess? Is it Piper's fault for having incorrect links, or is it Pied's fault for using those links? This issue might not be unique to just one language or voice model; it could potentially affect all JSON files. This is a critical question because the answer dictates who needs to implement the fix.
Is Piper the Culprit?
If Piper's voice list (like the one in VOICES.md) contains these incorrect links, then the onus is on Piper to update them. This would ensure that anyone using Piper directly or relying on its data gets the correct files. If Piper maintains the list of download links and these links are incorrect, then the fix needs to happen within the Piper project itself. It’s like having a bad map – you need to update the map, not just tell people to drive around the wrong turns.
Could Pied Be the Issue?
Alternatively, if Pied is referencing or storing the links incorrectly, the fix needs to happen within the Pied snap. This could involve correcting how Pied fetches or handles these links. If Pied is responsible for fetching the model files, it needs to ensure it’s using the correct URLs. It's possible that Pied is misinterpreting the links or adding the extra .json suffix during the download process. This would mean the issue lies in how Pied handles the download links. We need to ensure that Pied is correctly handling the download links and not introducing the .json suffix.
A Likely Broader Issue: All JSON Files
It's highly probable that this isn't an isolated incident. If one JSON file download is broken, there's a good chance others are too. This implies a systemic issue in how these files are being downloaded or referenced. Therefore, the fix needs to be comprehensive, addressing all JSON files to prevent future errors. We need to look at the download process for all JSON files, not just the one identified, to ensure we’ve covered all bases.
Steps to Resolve the Issue
To resolve this issue effectively, several steps should be taken to ensure a seamless experience for users of Piper and Pied.
Step 1: Verify and Correct Download Links
The initial step involves verifying the download links for all voice models. The focus should be on ensuring the links for JSON files are accurate. Any link ending with a faulty suffix like ?download=true.json needs immediate correction. This might involve checking the master list of voice models and their corresponding download URLs. We need to meticulously review all download links to catch any other potential errors.
Step 2: Update Piper's Voice List
If the issue originates from Piper's voice list, the list needs updating with the correct download links. This ensures that anyone using Piper's default configuration will receive the correct JSON files. This step is essential for the broader Piper community, as many users rely on the default voice lists. It's like correcting a central database that many users depend on.
Step 3: Patch Pied's Download Mechanism
If Pied is at fault, the mechanism by which it downloads the JSON files needs patching. The patch should ensure that the correct URLs are used and no extra suffixes are added during the download process. This might involve modifying Pied’s code to correctly parse and use the download links. It’s crucial to ensure Pied isn’t inadvertently altering the URLs during the download process.
Step 4: Distribute the Fix
Once the appropriate fixes are in place, they need to be distributed to users. For Piper, this might mean releasing a new version or updating the voice list. For Pied, this means pushing an updated snap package to the Snap Store. This step is all about getting the fix out to the users, whether it’s through a new release or an update. It’s the final mile in the resolution process.
Step 5: Inform the Community
Finally, informing the community about the issue and the fix is essential. This can be done through blog posts, release notes, or forum discussions. Keeping users in the loop ensures they are aware of the problem and know how to resolve it. We need to make sure users are aware of the issue and how to resolve it. This could involve posting on forums, writing blog posts, or including information in release notes.
Conclusion: A Collaborative Effort
In conclusion, the issue with Piper and the incorrect JSON download addresses highlights the importance of accurate links and proper download mechanisms. Whether the root cause lies in Piper or Pied, resolving it requires a collaborative effort. By verifying and correcting download links, updating voice lists, patching download mechanisms, and informing the community, we can ensure a seamless text-to-speech experience for everyone. This is all about ensuring a smooth and reliable text-to-speech experience for everyone. It's a great example of how collaborative troubleshooting can lead to a better user experience for everyone involved.
So, let’s roll up our sleeves and get this fixed, guys! Happy synthesizing!