不是什麼魔法，其實是改產品面上的規格 (但是發表到 Instagram Engineering 上)：「Video Upload Latency Improvements at Instagram」。
最原始的版本是所有的格式都轉完後才可以上架：
然後把規格改成最高畫質的版本轉完後就可以先上架：
The idea is, instead of blocking until all video versions are available, we can publish the video once the highest-quality video version is available.
然後是把影片切段上傳，所以傳一半就可以先處理一半，變成 pipeline 的概念，但增加程式的複雜度，以及被迫要調整影片品質的參數：
Segmented uploads reduce upload latency in many cases but come with a few tradeoffs. For instance, segmented uploads increase the complexity of the pipeline. There are some quality metrics that are only available per segment at transcode time, such as SSIM. These metrics are not helpful to us on a per segment basis. Therefore, we need to do a duration weighted average of the SSIM of all segments to come up with the SSIM of the whole video. Similarly, handling exceptions is more complex since there are more cases to handle.
另外有一種特例是上傳的影片本身就已經符合伺服器的規格，這樣的話可以直接放行 (不過這樣不會有 security concern 嗎...)：
Another performance optimization we use to improve the upload latency and save CPU utilization is something we call a “passthrough” upload. In some cases, the media that is uploaded is already ready for playback on most devices.
都是想的出來而且會帶有 tradeoff 的方法，而不是完全正面的改善 :o
