It's up in the URL: a string of eleven characters

就在網址裡面：一列共11位的字元，

that uniquely identifies which video you want.

用來顯示出你要的影片。

Now, YouTube has millions and millions of videos.

時至今日，YouTube 上有數以百萬計的影片。

The last stats that they released said they have

最近有統計指出在 YouTube

400 hours of video being uploaded every minute.

每分鐘有超過400小時的影片被上傳

So: are they ever going to run out of those IDs?

那麼問題來了：「代碼會有用盡的一天嗎？」

Well, to find out, let's talk about counting systems.

嗯，要想知道著個答案，我們先來談談記數系統

People count in Base 10. 0 to 9.

我們人類數數以 10 為底，從 0 到 9。

That'll be, hopefully, familiar to you.

關於這點，希望你不會感到陌生

Computers count in base 2, in binary,

電腦 (計算機) 則是以 2 為底的 2 進位，

but that's difficult for humans to read,

但那對我們人類閱讀上來說有困難

it gets too long to write really, really quickly,

因為要在短時間內寫下來實在是太長了

so often computers will display it in base 16, hexadecimal.

所以來說一般在電腦 (計算機) 上是以 16為底的 16 進位

You have 0 to 9, and then A to F,

你會從 0 算到 9 再來是 A 到 F (10 ~ 15)，

and then you start adding to the next column.

之後你再進到下一位。

Humans can't understand that easily,

對於 16 進位人類無法一看就懂，

but it's efficient if we have to type it in somewhere,

但若是要記下來的話還是可以的，

and 16 - 2 to the power of 4 - is also easy for computers to deal with.

再說16，也就是 2 的 4 次方，對電腦 (計算機) 來說也是很容易處理的。

So how about Base 64?

那麼 64 進位呢？

That'd be a ridiculous counting system, right? Except.

你想說那是個很愚蠢的記數方式，是吧？然而，

64 is another one of those easy numbers for computers,

64 對電腦 (計算機) 來說只不過是另一個簡單的數字罷了

it is 2 to the power of 6.

它 (64) 是 2 的 6 次方

And humans can get to 64 very easily:

人類想要湊出 64 也並非難事：

0 to 9, then capital letters A to Z,

從 0 到 9，然後大寫的 A 到 Z

then small letters a to z, and two other characters.

再加上小寫的 a 到 z，最後再加兩個其他符號。

Most Base 64 uses slash and plus,

大部分的時候是用 / 和 + (斜線和加號)

but they don't work so well in URLs,

但在網址中他們有別的功能，

so YouTube uses hyphen and underscore.

所以 YouTube 改用 - 和 _ (連字號和底線)

That YouTube URL, that unique ID,

我們說的 YouTube 的網址，那串獨一無二的代碼

is really just a random number in base 64.

就只是一串以 64 為底的亂碼罷了。

They could have have picked base 10 or base 16,

他們 (YouTube) 大可選用以 10 為底或是以 16 為底，

but they didn't: they went with 64,

但他們 (YouTube) 沒有：他們選擇以 64 為底，

because it will let you cram a huge number into a small space

如此一來便可將一個巨大的數字壓縮成短短的幾位數

and still make it vaguely human readable.

並且讓人類在某種程度上是可閱讀的

Author and programmer Sam Hughes, by the way,

順帶一提，身為作家和工程師的 Sam hughes

pushed this to the limit, and invented Base 65,536,

將此一方法發揮到了極致，創造了 65536 進位，

which includes basically every character from every language.

這種進位法也囊括了幾乎所有語言的所有字符。

It is ridiculous and unnecessary,

這無疑是可笑且無用的，

but when has that ever stopped programmers?

但工程師們從來就是對此一行為樂此不疲。

So why didn't YouTube just start counting at 1 and work up?

那麼為什麼 YouTube 不從 1 開始然後往上加就好了呢？

Well, first, they would have to synchronise their counting

這麼說吧，若是如此他們首先必須要

between all the servers handling the video uploads,

先將負責上傳影片的伺服器同步，或是

or they'd have to assign each server a block of numbers.

他們必須要先劃分清楚每一台伺服器負責的數字區間。

Either way, there's a lot of tracking to do,

但無論以上哪種方法，都要不斷的檢查、

a lot of making sure that it's never duplicated.

重複確認影片的編號絕對不會重複。

Instead, they just generate a random number for each video,

相反地，現在他們只要為每一部影片產出一組亂數，

see if it's already taken, and if not, use it.

並確認該組亂數沒有被使用就夠了。

And secondly, it is a really, really bad idea

第二點，在網址中使用單純的

to just count 1, 2, 3 and so on in URLs.

1, 2, 3 等等的數字絕對不是一個好主意。

Incremental counters, as they're called, can be a big security flaw:

使用遞增記數的話，會產生非常嚴重的安全漏洞：

if you see video 283 up there, then you might wonder:

如果你看見了一個編號 283 的影片，你一定會想：

what's video 284? Or video 282?

編號 284 的影片是什麼？那 282 呢？

It's easy to enumerate, as it's called,

這種編排法是很容易被類推的，

to run through the entire list.

換句花說：很容易被看光光。

YouTube Unlisted videos, the ones that don't appear publicly

用遞增記數的話就做不到影片非公開了（YouTube 上的非公開影片，

but that you can send the link to people, those wouldn't work.

雖說是非公開，但你仍然可以把網址發給你的朋友。）

And by the way? Lots of badly designed sites do use incremental counters.

喔對了，有不少設計不良的網站就是用這種遞增記數的

And it is a terrible idea.

真的是遭透了。

It might tell your competitors exactly how many customers you have,

這就好像在告訴你的競爭對手說你有多少使用者，

'cos they can just count them.

他們只要稍微數一下就知道了。

It might let people download all your records easily,

也很容易讓有心人下載你所有的記錄，

'cos they can just run through them.

只要他們把數字都試了個遍。

And in one site that someone in Florida emailed me about this week,

有個在佛羅里達州的人跟我說他知道有個網站，

it lets you look at other people's personal details.

甚至讓你有辦法查看其他人的個人資料。

Don't use incremental counters if you're building a web site. Use a random number.

如果你要架設網站的話請記住要用『亂數』， 『不、要、用、遞、增、記、數』

Which brings me to the question:

回到我們的問題：

just how big are the numbers that YouTube uses?

YouTube 到底用了多大的數字？

Well, let's work it out.

我們來算一下吧。

One character of base 64 lets you have 64 ID numbers.

64 進位的一位數可以有 64 個不同的 ID

Two characters? That's 64 by 64, or 4,096.

兩位數？就是 64 x 64 = 4096

Three characters? 64 times 64 times 64 -- or 64 to the power of 3.

三位？64 x 64 x64 或是 64 的三次方。

That is already more than a quarter of a million.

而這個數字已經超過 25 萬了

And if we go to four? Well, now we're above 16 million.

四位數呢？那就是大於 1600 萬了

If you use Base 64, then you can assign an ID number

如果用 64 進位的話，就可以生產出足以

to everyone who lives in London down there twice over,

超出倫敦居住人口數兩倍的影片代碼了，

and you'll only need four characters.

而這，僅僅只用了四、位、數。

This gets big fast. We can keep on doing this,

這數字成長的飛快。若我們繼續下去的話

and by seven characters we're already at four quadrillion.

當我們用了七位數的時候就會得到超過 四兆 組的代碼。

Now, I assume that YouTube checks through a dictionary,

呃...在這邊我希望 YouTube 有先檢查過，

and doesn't allow any actual words to appear up there --

確保上面那串代碼不會有「單字」的出現

particularly anything rude.

尤其是那些不好的字眼

But that is going to be a tiny minority of the URLs,

當然那只佔了眾多網址中一小部分罷了，

so for our purposes, we can pretty much just ignore that.

所以在這邊我們可以暫時先忽略那些

At YouTube's 11 characters, we are at 73 quintillion 786 quadrillion

而 YouTube 用 11 位數產生的代碼可供 7378 京 (京：10^16)

976 trillion 294 billion 838 million

6976 兆 2948 億

206 thousand and 464 videos.

3820 萬 6464 部影片使用

That's enough for every single human on planet Earth

而這足以讓這顆星球上的 每、一、個、人

to upload a video every minute for around 18,000 years.

以每分鐘上傳一部影片的速度，持續大約18000年

YouTube planned ahead.

YouTube 在這方面領先群雄啊

Can they run out of URLs? Technically, yes.

他們的網址會有用完的一天嗎？ 理論上來說，會。

Practically? No. And if they did?

實際上呢？並不會。 但如果真的用完的話呢？

They could just add one more character.

他們只需要再進一位就好啦（11--->12）

[Translating these subtitles? Add your name here!]

翻譯：Andy Lin

Ha! One take! One take! Yes!

哈！一鏡到底！一鏡到底啦！YES！