Changes to the WebM file format

Oct 13, 2025 by magicalceylontours.com 92 views

Uncaught Error: Current Matroska Cluster Exceeded Its Maximum Allowed Length When Muxing Both Audio and Video

Problem

When attempting to mux both audio and video, you may encounter the error Uncaught Error: Current Matroska cluster exceeded its maximum allowed length of 32768 milliseconds. In order to produce a correct WebM file, you must pass in a key frame at least every 32768 milliseconds. even if keyframes are placed correctly at or before the 32768ms mark. This issue arises due to the writing logic's assumption that the first chunk in a cluster will always be a video frame. However, this assumption can lead to an audio chunk extending the size of the current cluster, resulting in the error.

Cause

The root cause of this issue lies in the writing logic of the Matroska cluster. The logic assumes that the first chunk in a cluster will always be a video frame. However, this assumption is not always true, especially when muxing both audio and video. When an audio chunk is queued, it is added to the current cluster, even if the cluster is not yet full. This can cause the audio chunk to extend the size of the current cluster, resulting in the error.

To illustrate this issue, let's consider an example. Suppose we have audio chunks with timestamps (ms) as follows:

  [ 
    0,
    33000 // <-- need to be written in second cluster
  ]

And video frames at:

  [ 
    0,
    33001 // <-- will create second cluster
  ]

At the time we encode the second video frame, currentCluster is still the first cluster we created. The audio chunk is queued. Since we encode all audio chunks before the video chunk, we try to add the audio chunk to the wrong cluster. This results in the audio chunk extending the size of the current cluster, leading to the error.

Proposed Fix

To resolve this issue, we propose allowing the creation of new chunks from queued audio chunks, even if we are also muxing video in the same file. This will ensure that audio chunks are added to the correct cluster, preventing the error from occurring.

Here's an example of how this can be implemented:

// Create a new chunk from the queued audio chunk
if (audioChunks.length > 0) {
  const newChunk = new Chunk();
  newChunk.addAudioChunk(audioChunks.shift());
  clusters.push(newChunk);
}

By implementing this fix, we can ensure that audio chunks are added to the correct cluster, preventing the error from occurring. This will result in a correct WebM file being produced.

Benefits of the Proposed Fix

The proposed fix has several benefits, including:

Improved accuracy: By allowing the creation of new chunks from queued audio chunks, we can ensure that audio chunks are added to the correct cluster, resulting in a more accurate WebM file.
Reduced errors: The proposed fix will reduce the occurrence of the error Uncaught Error: Current Matroska cluster exceeded its maximum allowed length of 32768 milliseconds.
Enhanced reliability: By implementing this fix, we can enhance the reliability of the WebM muxer, ensuring that it produces correct WebM files even when muxing both audio and video.

Conclusion

In conclusion, the error Uncaught Error: Current Matroska cluster exceeded its maximum allowed length of 32768 milliseconds. occurs when muxing both audio and video due to the writing logic's assumption that the first chunk in a cluster will always be a video frame. By allowing the creation of new chunks from queued audio chunks, we can resolve this issue and produce correct WebM files. The proposed fix has several benefits, including improved accuracy, reduced errors, and enhanced reliability.
Uncaught Error: Current Matroska Cluster Exceeded Its Maximum Allowed Length When Muxing Both Audio and Video - Q&A

Q: What is the cause of the error `Uncaught Error: Current Matroska cluster exceeded its maximum allowed length of 32768 milliseconds.`?

A: The error occurs due to the writing logic's assumption that the first chunk in a cluster will always be a video frame. However, this assumption is not always true, especially when muxing both audio and video. When an audio chunk is queued, it is added to the current cluster, even if the cluster is not yet full. This can cause the audio chunk to extend the size of the current cluster, resulting in the error.

Q: What is the proposed fix for this issue?

A: The proposed fix is to allow the creation of new chunks from queued audio chunks, even if we are also muxing video in the same file. This will ensure that audio chunks are added to the correct cluster, preventing the error from occurring.

Q: How does the proposed fix work?

A: The proposed fix involves creating a new chunk from the queued audio chunk and adding it to the cluster. This ensures that the audio chunk is added to the correct cluster, preventing the error from occurring.

Q: What are the benefits of the proposed fix?

A: The proposed fix has several benefits, including:

Improved accuracy: By allowing the creation of new chunks from queued audio chunks, we can ensure that audio chunks are added to the correct cluster, resulting in a more accurate WebM file.
Reduced errors: The proposed fix will reduce the occurrence of the error Uncaught Error: Current Matroska cluster exceeded its maximum allowed length of 32768 milliseconds.
Enhanced reliability: By implementing this fix, we can enhance the reliability of the WebM muxer, ensuring that it produces correct WebM files even when muxing both audio and video.

Q: Can you provide an example of how the proposed fix can be implemented?

A: Yes, here's an example of how the proposed fix can be implemented:

// Create a new chunk from the queued audio chunk
if (audioChunks.length > 0) {
  const newChunk = new Chunk();
  newChunk.addAudioChunk(audioChunks.shift());
  clusters.push(newChunk);
}

Q: How can I test the proposed fix?

A: To test the proposed fix, you can create a test scenario where you are muxing both audio and video. Then, you can add the proposed fix to the code and test it to see if the error is resolved.

Q: What are the potential risks of implementing the proposed fix?

A: The potential risks of implementing the proposed fix include:

Changes to the WebM file format: The proposed fix may require changes to the WebM file format, which could potentially break existing code that relies on the current format.
Incompatibility with certain players: The proposed fix may cause incompatibility issues with certain players that do not support the new chunk format.

Q: How can I ensure that the proposed fix is safe to implement?

A: To ensure that the proposed fix is safe to implement, you should:

Thoroughly test the fix: Test the fix in a variety of scenarios to ensure that it works correctly and does not cause any issues.
Review the code changes: Review the code changes to ensure that they are correct and do not introduce any new bugs.
Consult with experts: Consult with experts in the field to ensure that the fix is safe to implement and does not cause any issues.

Q: What are the next steps after implementing the proposed fix?

A: After implementing the proposed fix, you should:

Monitor the fix: Monitor the fix to ensure that it is working correctly and does not cause any issues.
Test the fix: Continue to test the fix in a variety of scenarios to ensure that it works correctly.
Review the code changes: Review the code changes to ensure that they are correct and do not introduce any new bugs.