1593790 - createImageBitmap creates an untranslated version of videos

Status: NEW

(Core :: Graphics: Canvas2D, defect, P3)

Description

[Dave Townsend [:mossop] (PTO until Aug 21st)]

MP4 videos can include a matrix to translate the rendered video. This is commonly used to rotate the video to portrait for a video recorded as landscape. Firefox and Chrome correctly apply this matrix when rendering in a <video> element. However using createImageBitmap to capture a frame of a video that is translated in this fashion behaves differently in Firefox and Chrome.

In Chrome you get an ImageBitmap containing the translated image and width/height, so exactly what you see in the page. Rendering it in a canvas shows the same image.

In Firefox you get an ImageBitmap containing the untranslated image and the untranslated withd/height. I.e. for a landscape image that is translated to display as portrait the generated ImageBitmap is landscape. Rendering it to a canvas shows a rotated version of the frame.

The spec for createImageBitmap doesn't cover what should happen in this case but Chrome's behaviour makes the most sense to me, I would expect capturing a frame from a playing video to give a bitmap the same shape as the video.

Comment 1

[Dave Townsend [:mossop] (PTO until Aug 21st)]

Looks like this also impacts ctx.drawImage(video_element) on a canvas element.