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译文提交 - “一个更好的视频码头”（An even Better Video Wharf） (#29086)
* 申请翻译 ID: Drwhooooo 时间：2023/4/6 - 15:30 * 译文提交 - “一个更好的视频码头”（An Even Better Video Wharf） 译者ID : Drwhooooo * 译文提交 - “一个更好的视频码头”（An Even Better Video Wharf） 译者ID : Drwhooooo * Rename 目标语言/技术/20210111 an even better video wharf.md to translated/tech/20210111 an even better video wharf.md --------- Co-authored-by: Xingyu.Wang <xingyu.wang@gmail.com>
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[#]: subject: "an even better video wharf"
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[#]: via: "https://jao.io/blog/2021-01-11-an-even-better-video-wharf.html"
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[#]: author: "jao https://jao.io"
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[#]: collector: "lujun9972"
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[#]: translator: "Drwhooooo"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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an even better video wharf
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======
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A couple of days ago, [i was writing][1] about [embark][2] and my first experiment defining a new embarking to play remote video streams. Omar Antolín Camarena, embark's author, has been kind enough to not only read it, but comment on a couple of significant improvements that i think well deserve this follow-up.
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First, you'll remember that we were defining a function to detect a video URL:
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```
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(defun jao-video-finder ()
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"Check whether we're looking at a video URL.
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Return (video-url . <URL>) if so."
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(when-let ((url (thing-at-point-url-at-point)))
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(when (string-match-p jao-video-url-rx url)
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(cons 'video-url url))))
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```
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Once we've got a non-null `url` value, even if it's not a video URL, it's still certainly a URL, and embark has a `url` category, so we could save a new parsing by the default URL finder by saying:
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```
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(when-let ((url (thing-at-point-url-at-point)))
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(cons (if (string-match-p jao-video-url-rx url) 'video-url 'url) url))
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```
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This has the potential drawback that we're overriding embark's finder, `embark-target-url-at-point`, and we might prefer to keep the latter.
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Turns out that we can do that thanks to embark's _target transformers_. One can add to `embark-transformers-alist` an arbitrary function to be applied to a target of any given category, and embark will apply its actions to the transformed value. Omar calls this process, very aptly, a refinement of the target; here's how we would do it:
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```
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(defun jao-refine-url-type (url)
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"Refine type of URL in case it is a video."
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(cons (if (string-match-p jao-video-url-rx url) 'video-url 'url) url))
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(add-to-list 'embark-transformer-alist '(url . jao-refine-url-type))
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```
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With this strategy, we don't need `jao-video-finder` at all, and it also makes lots of sense, conceptually, to have our `video-url` defined as a refinement rather than a new target[1][3]. Omar's second suggestion is also in line with this concept: surely we want all actions available for `url` also for our `video-url`, don't we? Well, that's exactly the reason why the `embark-define-keymap` macro we used to define our actions can inherit all the actions already defined in another keymap, using the `:parent` keyword[2][4]:
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```
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(embark-define-keymap jao-video-url-map
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"Actions on URLs pointing to remote video streams."
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:parent embark-url-map
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("p" jao-play-video-url))
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(add-to-list 'embark-keymap-alist '(video-url . jao-video-url-map))
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```
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It is worth noting that this ability to inherit a keymap is not really an embark add-on: vanilla Emacs keymaps already have it, via the standard function `set-keymap-parent`. You could actually define `jao-video-url-map` without using `embark-define-keymap` at all, and it'd work exactly the same.
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So, our code has become shorter and more featureful: thanks, Omar!
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### Footnotes:
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[1][5]
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There's a scenario where keeping jao-video-finder could make sense, namely, if we want to alter the URL detection function. For instance, i use emacs-w3m, and there often a URL is stored as a text property (the actual text being the link text). To retrieve the URL at point there, one needs to call `w3m-anchor`, and `embark-target-url-at-point` will miss it. For that scenario, i ended up writing (and using) `jao-video-finder` defined with:
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```
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(when-let ((url (or (w3m-anchor) (thing-at-point-url-at-point))))
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(cons (if (string-match-p jao-video-url-rx url) 'video-url 'url) url))
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```
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Another way of accomplishing the same thing (with another tip of the hat to Omar) would be to add a specific finder for w3m anchors (and keep using the transformer for video-url):
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```
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(defun jao-w3m-url-finder ()
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(when-let ((url (w3m-anchor)))
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(cons 'url url)))
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(add-to-list 'embark-target-finders #'jao-w3m-url-finder)
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```
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This way is more modular and, depending on your taste, more elegant. These functions are small and there's not a big difference between the two approaches, but if one keeps adding finders, things can easily get uglier with the former approach.
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[2][6]
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In my original example, i was adding also `browse-url` and `browse-url-firefox` to the video map. The former is no longer necessary, because it's already present in `embark-url-map`. If we wanted to make `browse-url-firefox` available to _all_ URLs, we could add it to `embark-url-map` (remember, embark's keymaps are just Emacs keymaps). That's yet another simple way of extending embark.
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[Tags][7]: [emacs][8]
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--------------------------------------------------------------------------------
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via: https://jao.io/blog/2021-01-11-an-even-better-video-wharf.html
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作者：[jao][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://jao.io
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[b]: https://github.com/lujun9972
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[1]: https://jao.io/blog/2021-01-09-embarking-videos.html
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[2]: https://github.com/oantolin/embark
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[3]: tmp.VUqMT3Yft2#fn.1
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[4]: tmp.VUqMT3Yft2#fn.2
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[5]: tmp.VUqMT3Yft2#fnr.1
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[6]: tmp.VUqMT3Yft2#fnr.2
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[7]: https://jao.io/blog/tags.html
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[8]: https://jao.io/blog/tag-emacs.html
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121
translated/tech/20210111 an even better video wharf.md
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121
translated/tech/20210111 an even better video wharf.md
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@ -0,0 +1,121 @@
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[#]: subject: "an even better video wharf"
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[#]: via: "https://jao.io/blog/2021-01-11-an-even-better-video-wharf.html"
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[#]: author: "jao https://jao.io"
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[#]: collector: "lujun9972"
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[#]: translator: "Drwhooooo"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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一个更好的视频码头
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======
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几天前，[我在写][1] 有关 [embark][2] 的内容，我的第一设备为启动远程视频流设计了一个新的 embark。作为 embark 的作者，Omar Antolín Camarena，不仅阅读了这篇内容，还点评了一下我认为值得跟进的一些重大改进.
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首先，你应该记得我们曾定义过一个检测视频 URL 的函数：
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```
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(defun jao-video-finder ()
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"Check whether we're looking at a video URL.
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Return (video-url . <URL>) if so."
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(when-let ((url (thing-at-point-url-at-point)))
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(when (string-match-p jao-video-url-rx url)
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(cons 'video-url url))))
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```
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当我们得到了一个非空的 `url` 值，即便它不是一个视频链接，但它仍然是一个确切的 URL，并且 embark 已有了一个 `url` 类别，所以我们可以借助默认的 URL 寻检器存储一个新的句法分析,语句如下：
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```
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(when-let ((url (thing-at-point-url-at-point)))
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(cons (if (string-match-p jao-video-url-rx url) 'video-url 'url) url))
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```
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这里有一个潜在的缺点就是：我们重写了 embark 的寻检器，`embark-target-url-at-point`，所以我们可能更愿意保留后者。
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实际上多亏了 embark 的 _目标转换器_ 我们才能做成。我们可以在 `embark-transformers-alist` 中添加任意一个函数，应用于任何一个给定类别的目标，而 embark 会将其转换后的值应用于它的操作中。Omar 很贴切地把这个过程称为“目标的精化”;我们具体做法如下：
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```
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(defun jao-refine-url-type (url)
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"Refine type of URL in case it is a video."
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(cons (if (string-match-p jao-video-url-rx url) 'video-url 'url) url))
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(add-to-list 'embark-transformer-alist '(url . jao-refine-url-type))
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```
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通过这种策略，我们就不再需要 `jao-video-finder` 了，而且从概念上来说，我们的 `video-url` 应该被定义为一个精化操作而并非是一个目标[1][3]。Omar 的第二个提议也与这个概念相契合：想必我们都希望所有关于 `url` 和我们的 `video-url` 的操作都是可用的，不是吗？
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唔，这就是为什么我们用来定义行为的 `embark-define-keymap` 的宏可以通过使用关键字[2][4] `:parent` 继承其他键映射中已经定义的所有操作的原因：
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```
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(embark-define-keymap jao-video-url-map
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"Actions on URLs pointing to remote video streams."
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:parent embark-url-map
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("p" jao-play-video-url))
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(add-to-list 'embark-keymap-alist '(video-url . jao-video-url-map))
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```
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这种继承键映射的功能并非是 embark 的附属功能：vanilla Emacs 键映射通过标准函数 `set-keymap-parent` 已经搞定它了。你可以完全不用 `embark-define-keymap` 来定义 `jao-video-url-map`，工作原理是一样的。
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这样，我们的代码就能够更短，特征更多：谢谢你，Omar!
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### 脚注：
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[1][5]
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在某些情况下，保留 jao-video-finder 是有意义的，即，如果我们想要改变检测 URL 的功能的话。例如，我在使用 emacs-w3m 的时候，经常有一个 URL 作为文本属性储存了起来(实际文本是个链接文本)。要通过那里检索 URL，就需要调用 `w3m-anchor`，而用 `embark-target-url-at-point` 就会错过它。对于这种情况，我最终编写(并使用)`jao-video-finder` 将其通过下文定义:
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```
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(when-let ((url (or (w3m-anchor) (thing-at-point-url-at-point))))
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(cons (if (string-match-p jao-video-url-rx url) 'video-url 'url) url))
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```
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另一种达成同件事情的方式（再次向 Omar 致敬）便是为 w3m 的锚点放置一个特定的巡检器（且继续使用 video-url 的转换器）：
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```
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(defun jao-w3m-url-finder ()
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(when-let ((url (w3m-anchor)))
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(cons 'url url)))
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(add-to-list 'embark-target-finders #'jao-w3m-url-finder)
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```
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这种方法更加模块化，并且取决于你们的喜好，且更加巧妙。这些功能都很小巧并且两种方法之间并没有太大的差别，但是如果其中某一种继续加入更多寻检器的话，前一种方法用起来来反而会让一切变得更糟。
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[2][6]
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在我最开始的例子中，我在视频地图中还添加了 `browse-url` 和 `browse-url-firefox`。前一个已不再重要，因为它已经在 `embark-url-map` 中出现过了，如果我们想让 `browse-url-firefox` 对 _所有_ 的 URLs 可用,我们可以将其加入到 `embark-url-map` （谨记，embark 的键映射只是 Emacs 的键映射）。这是另一种扩展 embark 的简便方法。
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[标签][7]: [emacs][8]
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--------------------------------------------------------------------------------
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via: https://jao.io/blog/2021-01-11-an-even-better-video-wharf.html
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作者：[jao][a]
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选题：[lujun9972][b]
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译者：[Drwhooooo](https://github.com/Drwhooooo)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://jao.io
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[b]: https://github.com/lujun9972
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[1]: https://jao.io/blog/2021-01-09-embarking-videos.html
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[2]: https://github.com/oantolin/embark
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[3]: tmp.VUqMT3Yft2#fn.1
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[4]: tmp.VUqMT3Yft2#fn.2
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[5]: tmp.VUqMT3Yft2#fnr.1
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[6]: tmp.VUqMT3Yft2#fnr.2
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[7]: https://jao.io/blog/tags.html
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[8]: https://jao.io/blog/tag-emacs.html
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