Bug 290002 – Critical Issue: MediaRecorder Failing for video/mp4 variants on iOS 18.4 Beta

• Status: RESOLVED
• Resolution: DUPLICATE
• Component: WebRTC

[FS]

Hi there,

MediaRecorder is not working properly for recording video in Safari iOS 18.4 beta or any other iOS browsers (Chrome, Firefox) when using video/mp4 codec variants. This issue can be reproduced using the MediaRecorder sample. While the site isn’t mobile-optimized, the core problem is more severe—the lack of support for MP4 variants in iOS 18.4 beta.

Steps to Reproduce:
1. Click Start Camera and grant permissions.
2. Select any video/mp4 codec from the Recording format dropdown.
3. Click Start Recording—the recording proceeds as expected.
4. Click Play after recording. Instead of playing, a broken play icon appears, indicating playback failure.
This issue was not present in earlier iOS versions but is severe in 18.4 beta, consistently reproducible across three different iPhones running the beta.

This needs an urgent fix—breaking a previously functional feature is a significant regression! Looking forward to a swift resolution.

Thanks,
FS.

[FS]

(In reply to FS from comment #0)
> Hi there,
> 
> MediaRecorder is not working properly for recording video in Safari iOS 18.4
> beta or any other iOS browsers (Chrome, Firefox) when using video/mp4 codec
> variants. This issue can be reproduced using the MediaRecorder sample. While
> the site isn’t mobile-optimized, the core problem is more severe—the lack of
> support for MP4 variants in iOS 18.4 beta.
> 
> Steps to Reproduce:
> 1. Click Start Camera and grant permissions.
> 2. Select any video/mp4 codec from the Recording format dropdown.
> 3. Click Start Recording—the recording proceeds as expected.
> 4. Click Play after recording. Instead of playing, a broken play icon
> appears, indicating playback failure.
> This issue was not present in earlier iOS versions but is severe in 18.4
> beta, consistently reproducible across three different iPhones running the
> beta.
> 
> This needs an urgent fix—breaking a previously functional feature is a
> significant regression! Looking forward to a swift resolution.
> 
> Thanks,
> FS.

The URL to the site is: https://webrtc.github.io/samples/src/content/getusermedia/record/

[youenn fablet]

Thanks for the report, I believe this is fixed in https://bugs.webkit.org/show_bug.cgi?id=288459.

[youenn fablet]

*** This bug has been marked as a duplicate of bug 288459 ***

[FS]

Hi youenn, thanks for the reply. I have checked the most recent iOS 18.4 beta update and I still don't the issue being fixed there. 

As for the issue duplicate, I am not sure how they are connected. Can we get a little more explanation? Thanks!

[youenn fablet]

@FS, have you tried iOS 18.4 beta 4?
I would expect this beta to have the fix I mentioned, but not the previous iOS 18.4 beta 3.

[FS]

@youenn Yes I think it has been resolved in beta 4. We are still testing more thoroughly. Can we get a little more explanation reason for this issue? Thanks!

[Jean-Yves Avenard [:jya]]

The MediaRecorder internals have been fully rewritten to add support for webm and new codec support (hevc, av1, alas, pcm etc).
The crash in questions was due to a thread data race if a call to requestData was performed repeatedly while writing to the mp4 was pending.

This could only happen writing mp4. It wouldn't have affected webm recordings.

[FS]

Thanks for the update @Jean-Yves Avenard [:jya]. This helps clarify few things. 

We observe few things while testing the rewrites (so far it's good on video/mp4):

1. If the mimeType selected for MediaRecorder is video/mp4; codecs=avc1, it changes to video/mp4; codecs=avc1.42000a onstop or ondatavaailable events. We don't see an issue there, but an observation that makes us curious what and why is this added? 

2. If we use video/webm, we see the video recorded is rotated to landscape for a portrait video. I believe this has to be a new issue posted. 

Thanks again!

[Jean-Yves Avenard [:jya]]

1. The mime type returned is what was actually created as required by the spec. It doesn't have to be what the MediaRecorder was created with. Before MediaRecorder would only work with aac and h264. Now it can do much more, including generating HDR or > 8 bits content. As such `codecs=avc1` isn't sufficient. avc1 only was never correct anyway and wasn't following any standards. We kept support for it to ensure backward compatibility. 
2. Yes, this is a known issue. The webm container doesn't allow like mp4 to indicate in the metadata that the video should be rotated. We will have to physically rotate the image before compressing it.

[Jean-Yves Avenard [:jya]]

1. The mime type returned is what was actually created as required by the spec. It doesn't have to be what the MediaRecorder was created with. Before MediaRecorder would only work with aac and h264. Now it can do much more, including generating HDR or > 8 bits content. As such `codecs=avc1` isn't sufficient. avc1 only was never correct anyway and wasn't following any standards. We kept support for it to ensure backward compatibility. 
2. Yes, this is a known issue. The webm container doesn't allow like mp4 to indicate in the metadata that the video should be rotated. We will have to physically rotate the image before compressing it.

[FS]

@Jean-Yves Avenard [:jya],

On #1, thanks for the clarification. Few follow up question on this getting fixed on 18.4 beta 4, 
- Is there a exact/tentative timeline on when 18.4 will be publicly released?
- Is there a way we can detect if an iOS 18.4 is on beta < 4? We don't see User Agent being reliable for getting an idea on different versions of beta. 

On #2, we have reported the issue here: https://bugs.webkit.org/show_bug.cgi?id=290223. I believe it will be appropriate to follow up there. Thanks!