Bug 299164 – REGRESSION (iOS 26): MediaRecorder produces corrupted video/audio files, resulting in some loss of content

• Status: RESOLVED
• Resolution: FIXED
• Component: Media

[liuyun]

Hello WebKit Team,

We are writing to report a critical regression in the MediaRecorder API behavior observed in the iOS 26 beta. 
This issue is causing critical failures in our application, as well as in several other third-party libraries we have tested. After recording audio or video, the playback duration is significantly shorter than expected. For instance, a one-minute recording might only have 20 seconds captured correctly, with the remaining 40 seconds of content being lost.

We are unsure how to resolve this problem and would appreciate your confirmation and guidance. 

Thank you.

[Alexey Proskuryakov]

Thank you for the report! Could you please provide more information to make it actionable? E.g.
- whether this reproduces with iOS 26 release;
- a URL and steps for us to reproduce this;
- which hardware models you have seen this with.

[Radar WebKit Bug Importer]

<rdar://problem/160982017>

[liuyun]

Thank you for your reply.

-Yes, this issue occurs in iOS 26 release.

-I've provided a URL that demonstrates the problem：
  <https://addpipe.com/media-recorder-api-demo-audio>
  when you click on the video at this URL, the resulting MP4 file, which should be one minute long, only has 29 seconds of footage.

-I encountered this issue on my iPhone 13 Pro.
  I haven't observed this problem on Android devices or another versions of iOS (18).

Thank you.

[Jer Noble]

Is this unique to MP4 or does it happen when recording in WebM as well?

[liuyun]

Thanks for your reply.
-Yes, I've only found issues with MP4. I've tested WebM and found no issues. It's recording in WebM  fine.
Thank you!

[Jer Noble]

It looks like this is not unique to iOS; I can reproduce the same problem on macOS Safari 26, and only when the output file is .mp4.

[Jer Noble]

It also looks like it's the _end_ of the recording that's missing. A 30 second recording where I'm just listing numbers from 1-30 will cut off at around 15.

[Jean-Yves Avenard [:jya]]

Pull request: https://github.com/WebKit/WebKit/pull/51596

[EWS]

Committed 300824@main (812a4cd88295): <https://commits.webkit.org/300824@main>

Reviewed commits have been landed. Closing PR #51596 and removing active labels.

[liuyun]

Hello WebKit Team,

Thank you for your prompt reply.
It seems the issues mentioned above have been fixed, is that correct? 
I haven't seen an iOS version update yet. 
May I ask when this fix is approximately scheduled for release?

Thank you.

[Axel]

Hello WebKit Team

We are still encountering this issue on iOS 26.1: when using the MediaRecorder API, only the first 20–30 seconds of the recording are present in the final file. The behavior matches the original report for this bug.

I have not seen any reference to the associated fix in the release notes for iOS 26.1 or for the iOS 26.2 Beta 3 builds. Could you provide any information on whether the fix has been included in the 26.x branch, or when it is expected to ship?

Thanks for looking into this

[Alexey Proskuryakov]

Thank you for the follow up, this should be fixed in 26.2 beta 3 (probably earlier betas too).