Bug 287516 – WebCodecs VideoDecoder Outputs Frames in Incorrect Order

• Status: NEW
• Component: Media

Created attachment 474211 [details]
Video sample exhibiting the issue (if applicable).

Description:

When using the WebCodecs VideoDecoder API in Safari, video frames are received in an incorrect order. This issue does not occur in Chrome, where frames are correctly decoded and presented in the expected sequence.

Steps to Reproduce:

Use WebCodecs VideoDecoder to decode a video containing B-frames.

Observe the output frame order.

Expected Behavior:

The VideoDecoder should output frames in the correct display order, as specified by the video encoding and the WebCodecs specification.

Actual Behavior:

In Safari, the decoder appears to output frames in the wrong order, likely due to incorrect handling of B-frames. The raw samples are not monotonically ordered by their timestamp, yet Chrome correctly orders them upon decoding, whereas Safari does not.

Additional Observations:

Safari successfully decodes B-frames correctly in other videos (e.g., Big Buck Bunny), so this issue may be specific to certain video files.

The issue suggests that Safari’s VideoDecoder is not fully spec-compliant in handling reordering of frames.

[Radar WebKit Bug Importer]

<rdar://problem/145093697>

[Ahmad Saleem]

Does it impact any live website or product? Plus if you have any test case or minimal reduction to reproduce the issue?