1753086 - Incorrect starting or earliest possible position and origin of a media timeline

Status: NEW

(Core :: Audio/Video: Playback, defect, P3)

Description

[Ksenia Berezina [:ksenia]]

We've received a report in https://github.com/webcompat/web-bugs/issues/98307 about an issue where a video timeline is shown incorrectly- the video starts playing at 54:42, but the timeline is showing 0.

To reproduce:

1. Visit https://readingma.us/sites/default/files/2022-01/SelectBoard%2C2021-06-01%3DYouTube%3AzyAkAr0xI3E_SNIPPET.mp4 in Firefox and observe the timeline

Expected:
Timeline starts 54:42

Actual:
Timeline starts at 0

The reporter created the timeline using ffmpeg with the following command:
ffmpeg -ss '54:42' -i 'InVideo.mp4' -to '1:24:27' -c copy -copyts 'OutVideo.mp4'

This seems to be related to 521899, which is closed as duplicate of 498253, but it was closed as well.

Comment 1

[Bryce Seager van Dyk [:bryce] (he/him) - Not reading bugmail]

https://html.spec.whatwg.org/multipage/media.html#defineTimeline appears to be the relevant part of the spec. Specifically

if the media resource somehow specifies an explicit timeline whose origin is not negative (i.e. gives each frame a specific time offset and gives the first frame a zero or positive offset), then the media timeline should be that timeline.

There is also an example that follows in the spec specifically highlighting non-zero timelines.

Rather than dredge up a decade old bug (bug 498253), I suggest track any new work against this bug.

Comment 2

[Dennis Schubert [:denschub]]

Valid issue, but only affecting one site at the moment, so let's set P3 and revisit if this causes more widespread issues.