Firefox/Shutdown Decoders

Overview

Background

Suspending video element's video decoder, when the video element is in background tabs or is invisible even in the foreground tab, is a Firefox feature that reduces CPU/GPU & memory usage.

The mechanism is that, when a video element is invisible, we replace its original video decoder with blank video decoder which only produces white frames with right resolution and right time information. The original video decoder is released and the black video decoder is light so that we reduce CPU/GPU & memory usage.

Trade-off

The trade-off is that, while the suspended-video-element is switched back to be visible again, we should resume its original video decoder. The resuming operation must be asynchronous and might be time-consuming which depends on the resolution of the video file and whether it contains audio tracks or not.

Working flow

The following is a step-by-step description of suspending decoder working flow.

1. At the very beginning of the decoding framework, the raw media data is sent to demuxer.
2. Demuxer helps to separate a combined signal, e.g., a streaming can be separated into audio data and video data by demuxer. After that, audio and video data are sent to audio and video decoder separately.
3. In data decoding period, audio decoder keeps working as normal because a user may be listening to the music. But, Firefox uses a blank video decoder to replace current video decoder if the video element is invisible.

Overall Project Health

[GREEN]

Target Milestone

Firefox55

Engineer Owner

Tzuhao Kuo [:kaku]

QA Contact

Simona Badau <simona.marcu@softvision.ro>
Adrian Florinescu <adrian.florinescu@softvision.ro

MVP Scope-Bug Tracking

• bug 1293963 -[Meta] Suspend-video-decoder: phase-1 shipping
• tracking things only under the scope of phase-1 shipping.

Bugzilla query error

Array ( [type] => error [message] => http-bad-status [params] => Array ( [0] => 429 [1] => Unknown Error ) ) 1

• bug 1352007- [Meta] Suspend-video-decoder
• the highest level meta bug tracking all things related to the suspend-video-decoder feature.

Bugzilla query error

Array ( [type] => error [message] => http-bad-status [params] => Array ( [0] => 429 [1] => Unknown Error ) ) 1

• bug 1276556-[META] Tracking enable of background tab video decoder suspend
• tracking basic functionalities which are all completed

Bugzilla query error

Array ( [type] => error [message] => http-bad-status [params] => Array ( [0] => 429 [1] => Unknown Error ) ) 1

UX Spec

• UX Spec : [https://mozilla.invisionapp.com/share/K48PCVSEM UX Spec

others

Decoder resuming latency

While the suspended-video-element is switched back to be visible again, we should resume its original video decoder. The resuming operation must be asynchronous since we don't want to block the main thread and might be time-consuming which depends on the resolution of the video file and whether it contains audio tracks or not.

Currently, we have no way to boost the resuming time, however, we have telemetries for collecting the needed time of different resolutions on different platforms.