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用 OpenCV 處理 webcam 的背景，再用 pyfakewebcam 接回給視訊軟體用...

最近武漢肺炎的關係，導致蠻多人會在家裡使用視訊會議，但背景一直是個問題... 然後就看到這篇文章：「Open Source Virtual Background」。

作者用 python-opencv 先處理 webcam 進來的影像 (看起來不只去背，還加上了 hologram 的效果 XDDD)，然後再用 pyfakewebcam 與 v4l2loopback 模擬成一個 webcam 餵回給視訊軟體，結果就惡搞成這樣了：

話說回來，最近各電商平台的 webcam 與視訊機都缺貨，還好之前有買個便宜的頂著，不然就得開筆電了...

Amazon Redshift 會自動在背景重新排序資料以增加效能

Amazon Redshift 的新功能，會自動在背景重新排序資料以增加效能：「Amazon Redshift introduces Automatic Table Sort, an automated alternative to Vacuum Sort」。

版本要到更新到 1.0.11118，然後預設就會打開：

This feature is available in Redshift 1.0.11118 and later.

Automatic table sort is now enabled by default on Redshift tables where a sort key is specified.

重新排序的運算會在背景處理，另外帶一些行為學習分析：

Redshift runs the sorting in the background and re-organizes the data in tables to maintain sort order and provide optimal performance. This operation does not interrupt query processing and reduces the compute resources required by operating only on frequently accessed blocks of data. It prioritizes which blocks of table to sort by analyzing query patterns using machine learning.

算是丟著讓他跑就好的東西，升級上去後可以看一下 CloudWatch 的報告，這邊沒有特別講應該是還好... XD

用 CSS 貼 3D 場景的圖

看到一個 demo 展示瀏覽器內 CSS 的處理能力，看起來已經足夠到可以處理不少貼圖與光線效果的部分了：「CSS FPS」。

This is demo of a CSS powered 3D environment. Geometry is created with HTML elements and CSS transforms. Textures and lightmaps are composed by layering multiple background-images and colour is applied using CSS blend-modes.

不過遊戲應該會需要更多種類的效果，這部份目前應該還是得靠 javascript 來產生... (如果要在瀏覽器裡面跑)

Facebook 更新 iOS 應用程式，修正吃電問題

在「在 iOS 上不使用 Facebook App 時要完全砍掉 process」這邊提到了 Facebook 在 iOS 版的應用程式會在背景播放無聲音樂，導致吃電特別兇的問題，Facebook 的 Ari Grant 出來澄清是 bug 造成的，而非故意行為。

修正了兩個 bug，第一個是 network code 的部分：

The first issue we found was a “CPU spin” in our network code. A CPU spin is like a child in a car asking, “Are we there yet? Are we there yet? Are we there yet?”with the question not resulting in any progress to reaching the destination. This repeated processing causes our app to use more battery than intended. The version released today has some improvements that should start making this better.

第二個則是之前提到無聲 audio 的問題：

The second issue is with how we manage audio sessions. If you leave the Facebook app after watching a video, the audio session sometimes stays open as if the app was playing audio silently. This is similar to when you close a music app and want to keep listening to the music while you do other things, except in this case it was unintentional and nothing kept playing. The app isn't actually doing anything while awake in the background, but it does use more battery simply by being awake. Our fixes will solve this audio issue and remove background audio completely.

同時澄清並沒有要在背景更新取得地理位置資訊：

The issues we have found are not caused by the optional Location History feature in the Facebook app or anything related to location. If you haven't opted into this feature by setting Location Access to Always and enabling Location History inside the app, then we aren't accessing your device's location in the background. The issues described above don't change this at all.

理論上新版應該會省一點電了？

在 iOS 上不使用 Facebook App 時要完全砍掉 process

在「The Background Data and Battery Usage of Facebook’s iOS App」這邊提到 Facebook App 在 iOS 上使用了非常吃電的技巧來強制背景更新。

作者猜測，如果你把 Facebook App 設定成不允許背景更新，那麼 Facebook App 會利用 iOS 在「播放音樂」可以在背景執行來進行更新：(所以只是打開播放的 channel，但是沒有聲音)

My guess is that Facebook is hijacking audio sessions on iOS by keeping silent audio in the background whenever a video plays in the app. And because, by default, videos on Facebook auto-play on both Wi-Fi and Cellular and few people ever bother to turn it off, that means there's a high chance the Facebook app will always find a way to play a video, keep audio in the background, and consume energy to perform background tasks.

而且有些人也發現了類似的現象：

I'm not alone in noticing the mysterious "Facebook audio" background consumption, and video auto-play seems to me the most likely explanation at this point. I don't know if turning off auto-play may fix the problem, but I'd recommend doing that anyway to save data.

印象中我們家的 zonble 也有提過類似的事情，當時他好像還有抱怨不知道 Facebook App 在搞什麼鬼... Anyway，這就可以理解作者提到為什麼這麼吃電：

On my girlfriend's iPhone, for instance, iOS 9 reports 5 hours of on-screen usage for the last 7 days, and another 11 hours of background audio usage with Background App Refresh turned off.

我的想法是，如果不用的時候就按兩下 home 鍵把 Facebook App 整個踢出去，或者就如同作者建議用 Safari 開行動版本：

I wonder if Apple should consider additional battery controls to take action against shady practices like invisible background audio. What Facebook is doing shows a deep lack of respect for iOS users. I continue to recommend using Safari instead.