Firefox/Shutdown Decoders: Difference between revisions

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=Overview=
=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.
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.
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.


The drawback 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.
== 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.  
In the prototype (Phase 0), we have enabled this feature on the Firefox Nightly channel for any video element. We also add telemetry to collect needed information, especially on the resuming time. Currently (Phase 1), we are going to enable this feature on the Firefox Release channel for videos that is able to be resumed quickly and the criteria is '''1) videos without audio track''' or '''2) videos with both audio and video tracks but with low resolution (480P for now)'''. In the future (Phase 2), our goal is to enable this feature on all videos without observable latency while resuming.
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.
The following is a step-by-step description of suspending decoder working flow.
# At the very beginning of the decoding framework, the raw media data is sent to demuxer.
# At the very beginning of the decoding framework, the raw media data is sent to demuxer.
Line 15: Line 17:
[[File:Fx_Shutdown_Decoder_Architecture_v2.png|800px|frameless]]
[[File:Fx_Shutdown_Decoder_Architecture_v2.png|800px|frameless]]


=Overall Project Health=
<font color="green">'''[GREEN]'''</font>
=Target Milestone=
Firefox55


=Status=
=Engineer Owner=
==Phases==
Tzuhao Kuo [:kaku]
=='''Program Status'''==
{| class="wikitable"
! style="text-align: center;" | Milestone
! style="text-align: center;" | Target
! style="text-align: center;" | Status
|-
| Phase 1
| 54 on Nightly
! style="background:#00EC00;" |
|-
| Phase 2
|
! style="background:#FFFF00;" | NOT STARTED
|}


* '''Phase 1''': Using a blank video decoder to replace video decoder instead of shutdown decoders directly. In this phase, the mechanism is applied to 1) Low-resolution video (480P) and 2) Video film without audio track
=QA Contact=
* '''Phase 2''': We're going to enhance the mechanism and make sure it can apply to all video files.
Simona Badau <simona.marcu@softvision.ro>


= Testing =
= MVP Scope-Bug Tracking =
*{{Bug|1293963}} -[Meta] Suspend-video-decoder: phase-1 shipping
<onlyinclude>
<bugzilla>
{
    "blocks": "1293963",
    "include_fields": "id, priority, summary, status,resolution,assigned_to, last_change_time",
    "order": "bug_id"
}
</bugzilla>
</onlyinclude>


Test cases: [https://moztrap.mozilla.org/manage/cases/?pagenumber=1&pagesize=20&sortfield=created_on&sortdirection=desc&filter-tag=3802 Phase 1]
<bugzilla>
    {
        "id":["1345768", "1345403", "1309492", "1346120", "1346498", "1346116", "1309494", "1346705", "1345034", "1345339", "1344357", "1345179"],
        "include_fields": "id, priority, summary, status, resolution, assigned_to, last_change_time",
        "order": "bug_id"
    }
</bugzilla>




=Signoff-Report by Simona Badau <simona.marcu@softvision.ro> =
==Feature testing status: ==


== MVP Scope ==
==Bugs tracking ==
{{Bug|1293963}} - [Meta] Suspend-video-decoder: phase-1 shipping
<bugzilla>
<bugzilla>
     {
     {
         "blocks":[1293963],
         "id":["1348864", "1348432", "1346235"],
         "include_fields": "id, priority, component, assigned_to, summary, status, target_milestone"
         "include_fields": "id, priority, summary, status, resolution, assigned_to, last_change_time",
        "order": "bug_id"
     }
     }
</bugzilla>
</bugzilla>


=Other Resources=
=UX Spec=
* [https://goo.gl/0dylCY Meeting Minute]
*UX Spec : [https://mozilla.invisionapp.com/share/K48PCVSEM UX Spec


=Reference=
=others=
===Decoder resuming latency===
===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.
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.
Line 60: Line 72:
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.  
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.  


''Related telemetries'':
* [https://telemetry.mozilla.org/new-pipeline/dist.html#!cumulative=0&end_date=2016-08-28&keys=All!AV%252C241-480!V%252C241-480!AV%252C481-720&max_channel_version=nightly%252F51&measure=VIDEO_SUSPEND_RECOVERY_TIME_MS&min_channel_version=null&product=Firefox&sanitize=1&sort_keys=submissions&start_date=2016-08-18&table=0&trim=1&use_submission_date=0 VIDEO_SUSPENDED_RECOVERY_TIME_MS]
''Related bugs'':
* [https://bugzil.la/1272919 Bug 1272919 - Video shows the frame that was on screen when I switched from youtube to a different tab for a fraction of a second]
===Video element as content source===
The situation is about the video element itself is used as a content source and its decoder might be suspended at the same time. This issue could be split into two cases:
* Case 1: The decoder is suspended '''AFTER''' the {cpatureStream(), drawImage(), createImageBitmap()} is called.
* Case 2: The decoder is suspended '''BEFORE''' the {cpatureStream(), drawImage(), createImageBitmap()} is called.
'''Case 1''' is relatively easy, we could mark the video element as being a content source while {cpatureStream(), drawImage(), createImageBitmap()} is invoked and then its decoder should never be suspended.
'''Case 2''' is rather complicated. The critical issue is that resuming decoder is an async operation with latency. So, while {cpatureStream(), drawImage(), createImageBitmap()} is invoked on an already-suspended-video, there must be several "blank" frames been leaked, even though we resume the decoder immediately. To completely solve this problem, we must make "resuming decoder" a blocking operation, however, it might block the main thread; otherwise, we leak the blank frames.
''Related bugs'':
* [https://bugzilla.mozilla.org/show_bug.cgi?id=1284389 Bug 1284389 - Don't suspend video elements captured via mozCaptureStream()]
* [https://bugzilla.mozilla.org/show_bug.cgi?id=1295921 Bug 1295921 - Don't suspend video decoder for elements as sources to drawImage() and createImageBitmap()]
=== Optimizations ===
* [https://bugzil.la/1282710 Bug 1282710 - Suspend and resume foreground video decoders according to visibility events]
** done.
* [https://bugzil.la/1282012 Bug 1282012 - Seek to nearest keyframe when resuming videos with no audio]
** [https://bugzil.la/1294657 Bug 1294657 - Seek to nearest keyframe when resuming videos with no audio - with audio track but muted]
*** pending, excluded from phase 1.
** [https://bugzil.la/1294658 Bug 1294658 - Seek to nearest keyframe when resuming videos with no audio - with audio track but might be silent]
*** pending, excluded from phase 1.
** [https://bugzil.la/1294656 Bug 1294656 - Seek to nearest keyframe when resuming videos with no audio - no audio track]
*** done.
* [https://bugzil.la/1274919 Bug 1274919 - Resume suspended video decoders on tab mouse hover.]
** under review.
* [https://bugzil.la/1284389 Bug 1284389 - Don't suspend video elements captured via mozCaptureStream()]
** WIP.
* [https://bugzil.la/1295921 Bug 1295921 - Don't suspend video decoder for elements as sources to drawImage() and createImageBitmap()]
** WIP.
* Resume video when keyboard is used to change tags - Needs Bug
** For example, if it's possible to detect the direction of cycling and videos are within, say, 5 tabs of the current tab, then start decoding again.
** Need to hook into the tab navigation/change code and alert media elements, like bug 1274919
=== Telemetry ===
* '''Amount of time hidden''' - measure of user value (Bucket results by resolution; i.e. are 720p videos hidden less often?)
** [http://bugzil.la/1285419 Bug 1285419 - Telemetry to support background video decoder suspend: Hidden play time]
** [https://mzl.la/2c0493i VIDEO_HIDDEN_PLAY_TIME_MS]
** [http://bugzil.la/1287987 Bug 1287987 - Telemetry to support background video decoder suspend: Percentage hidden/total play time, keyed by audio presence and height ranges]
** [https://mzl.la/2c04hQl VIDEO_HIDDEN_PLAY_TIME_PERCENTAGE]
** [http://bugzil.la/1293145 Bug 1293145 - Telemetry to support background video decoder suspend: Percentage video-decode-suspended/total play time]
** [https://mzl.la/2c07M9s VIDEO_INFERRED_DECODE_SUSPEND_PERCENTAGE]
* '''Recovery time''' - measure of user cost (separate for noisy vs silent videos) (Bucket results by resolution; i.e. do 720p videos take longer to recover?)
** [https://bugzil.la/1294349 Bug 1294349 - Telemetry to support background video decoder suspend: Recovery time from video-decode-suspended]
** [https://mzl.la/2c947Iv VIDEO_SUSPEND_RECOVERY_TIME_MS]
* '''Key frame spacing''' - distribution allows better tuning
** [http://bugzil.la/1289668 Bug 1289668 - Telemetry to support background video decoder suspend: Inter-keyframe timings]
** [https://mzl.la/2c04Utr VIDEO_INTER_KEYFRAME_AVERAGE_MS]
** [https://mzl.la/2c956bN VIDEO_INTER_KEYFRAME_AVERAGE_PERCENTAGE]
=== Mochitests ===
* [https://bugzil.la/1284177 Bug 1284177 - Add tests for video suspend in background]
** done
* [https://bugzil.la/1294358 Bug 1294358 - Add test for suspended videos still fire 'ended' event]
** done
* [https://bugzil.la/1295844 Bug 1295844 - Test suspended videos with webm files]
** done
=Team=
'''Eng:''' Alastor Wu , JW Wang <br />
'''Program Management:'''Rachelle Yang <br />
'''UX:''' Mark, Morpheus  <br />
'''QA:'''  Simona Badau <simona.marcu@softvision.ro>
<br />
<br />

Revision as of 03:19, 23 March 2017

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.

Fx Shutdown Decoder Architecture v2.png

Overall Project Health

[GREEN]

Target Milestone

Firefox55

Engineer Owner

Tzuhao Kuo [:kaku]

QA Contact

Simona Badau <simona.marcu@softvision.ro>

MVP Scope-Bug Tracking

  • bug 1293963 -[Meta] Suspend-video-decoder: phase-1 shipping

Bugzilla query error

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


Bugzilla query error

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


Signoff-Report by Simona Badau <simona.marcu@softvision.ro>

Feature testing status:

Bugs tracking

Bugzilla query error

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


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.


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