我需要使用 ajax 向服务器发送一个 blob，但它最终可能会变得有点大，我想减少上传时间。我已经尝试过 jszip，但这只是在 zip 中给了我一个空文件。我也尝试过 btoa()，但事实证明编码值最终只是 [object Blob] 而不是实际的 blob 数据。我有哪些压缩 blob 的选项？

这是我用于 jszip 的代码:

var zip = new JSZip();
zip.file("recording.wav", blobFile);
var content = zip.generate();

然后我将“内容”附加到 FormData 对象并将其发送到服务器。在服务器端，我解码了 POST 数据(来自 base64)。 zip 文件打开得很好，但 recording.wav 是一个 0 长度的文件。

此外，我尝试使用找到的 LZW 实现 here .这是我用来压缩它的附加代码:

var compressed;
var reader = new FileReader();
reader.onload = function(event){
   compressed = LZW.compress(event.target.result);
};
reader.readAsText(blobFile);

然而，解压它返回 null。

最佳答案

警告:压缩音频文件之类的东西最好使用专门针对此类数据的算法来完成，也许是有损的。但是，我知道找到下面提供的合理无损实现有多么困难，我非常担心很难在 Javascript 中找到专门满足您需求的那种数据的良好实现。

无论如何，我也对 Javascript 中的压缩/解压缩有这种普遍的需求，我需要相同的算法来同时在客户端(浏览器)和服务器端(node.js)工作，我需要它来处理非常大的文件。我已经检查了 jszip，我还尝试了至少五六个其他算法中的 LZW 算法，但没有一个满足要求。我不记得每个具体的问题是什么，但足以说明在 javascript 中找到一个好的和快速的压缩器/解压缩器是非常困难的，它可以在服务器端和客户端工作并处理大文件!我尝试了至少十几种不同的压缩算法实现，最后选择了这个——它还没有让我失望!

更新

这是原始出处: https://code.google.com/p/jslzjb/source/browse/trunk/Iuppiter.js?r=2

来自一位名叫 Bear 的人 - 感谢 Bear，无论你是谁，你都是最棒的。 是LZJB:http://en.wikipedia.org/wiki/LZJB

更新 2

1. 更正了缺少分号的问题 - 不应再给对象非函数错误。
2. 此实现停止处理长度少于 80 个字符的数据。所以我更新了示例以反射(reflect)这一点。
3. 意识到 base64 编码/解码方法实际上暴露在为此版本传入的对象上，所以...
4. 目前看到我们可以对特定的 blob 类型做些什么——例如，最好的方法是图像与音频等，因为这对一般的 JS 人员很有用……将在这里更新找到的内容。

更新 3

对于来自 Bear 的原始 Iuppiter 源代码，有一个比我在下面发布的更好的包装器。它由 cscott 编写并在 github 上:https://github.com/cscott/lzjb

我将切换到这个，因为它也支持流。

下面是一个在 Node.js 中使用 wav 文件的例子。但是在复制这个例子之前，让我先告诉你一个坏消息，至少对于我试过的这个 wav 文件来说是这样:

63128 Jun 19 14:09 beep-1.wav 
63128 Jun 19 17:47 beep-2.wav
89997 Jun 19 17:47 beep-2.wav.compressed 

因此它成功地重新生成了 wav(并播放)。但是，压缩后的文件似乎比原始文件大。好拍。无论如何，尝试使用您的数据可能会很好，您永远不会知道，您可能会很幸运。这是我使用的代码:

var fs = require('fs');
var lzjb = require('lzjb');

fs.readFile('beep-1.wav', function(err, wav){

    // base 64 first
    var encoded = wav.toString('base64');
    // then utf8 - you  don't want to go utf-8 directly
    var data = new Buffer(encoded, 'utf8');
    // now compress
    var compressed = lzjb.compressFile(data, null, 9);
    // the next two lines are unnecessary, but to see what kind of
    // size is written to disk  to compare with the original binary file
    var compressedBuffer = new Buffer(compressed, 'binary');
    fs.writeFile('beep-2.wav.compressed', compressedBuffer, 'binary', function(err) {});
    // decompress
    var uncompressed = lzjb.decompressFile(compressed);
    // decode from utf8 back to base64
    var encoded2 = new Buffer(uncompressed).toString('utf8');
    // decode back to binary original from base64
    var decoded = new Buffer(encoded2, 'base64');
    // write it out, make sure it is identical
    fs.writeFile('beep-2.wav', decoded, function(err) {});

});

归根结底，我认为要对大多数形式的二进制数据实现任何级别的压缩都太困难了，这些数据不会被生成的 base64 编码破坏。终端控制字符的日子至今仍困扰着我们。您可以尝试升级到不同的基础，但这也有其风险和问题。

例如看这个: What is the most efficient binary to text encoding?

还有这个: Why don't people use base128?

但有一件事，在您接受答案之前，请务必在您的 blob 上尝试一下，我主要将它用于压缩 utf-8，我想确保它适用于您的特定数据。

无论如何，它就在这里!

/**
$Id: Iuppiter.js 3026 2010-06-23 10:03:13Z Bear $

Copyright (c) 2010 Nuwa Information Co., Ltd, and individual contributors.
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice,
     this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
     documentation and/or other materials provided with the distribution.

  3. Neither the name of Nuwa Information nor the names of its contributors
     may be used to endorse or promote products derived from this software
     without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

$Author: Bear $
$Date: 2010-06-23 18:03:13 +0800 (星期三, 23 六月 2010) $
$Revision: 3026 $
*/
var fastcompressor = {};
(function (k) {
    k.toByteArray = function (c) {
        var h = [],
            b, a;
        for (b = 0; b < c.length; b++) a = c.charCodeAt(b), 127 >= a ? h.push(a) : (2047 >= a ? h.push(a >> 6 | 192) : (65535 >= a ? h.push(a >> 12 | 224) : (h.push(a >> 18 | 240), h.push(a >> 12 & 63 | 128)), h.push(a >> 6 & 63 | 128)), h.push(a & 63 | 128));
        return h
    };
    k.Base64 = {
        CA: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
        CAS: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
        IA: Array(256),
        IAS: Array(256),
        init: function () {
            var c;
            for (c = 0; 256 > c; c++) k.Base64.IA[c] = -1, k.Base64.IAS[c] = -1;
            c = 0;
            for (iS = k.Base64.CA.length; c < iS; c++) k.Base64.IA[k.Base64.CA.charCodeAt(c)] = c, k.Base64.IAS[k.Base64.CAS.charCodeAt(c)] = c;
            k.Base64.IA["="] = k.Base64.IAS["="] = 0
        },
        encode: function (c, h) {
            var b, a, d, e, m, g, f, l, j;
            b = h ? k.Base64.CAS : k.Base64.CA;
            d = c.constructor == Array ? c : k.toByteArray(c);
            e = d.length;
            m = 3 * (e / 3);
            g = (e - 1) / 3 + 1 << 2;
            a = Array(g);
            for (l = f = 0; f < m;) j = (d[f++] & 255) << 16 | (d[f++] & 255) << 8 | d[f++] & 255, a[l++] = b.charAt(j >> 18 & 63), a[l++] = b.charAt(j >> 12 & 63), a[l++] = b.charAt(j >> 6 & 63), a[l++] = b.charAt(j & 63);
            f = e - m;
            0 < f && (j = (d[m] &
                255) << 10 | (2 == f ? (d[e - 1] & 255) << 2 : 0), a[g - 4] = b.charAt(j >> 12), a[g - 3] = b.charAt(j >> 6 & 63), a[g - 2] = 2 == f ? b.charAt(j & 63) : "=", a[g - 1] = "=");
            return a.join("")
        },
        decode: function (c, h) {
            var b, a, d, e, m, g, f, l, j, p, q, n;
            b = h ? k.Base64.IAS : k.Base64.IA;
            c.constructor == Array ? (d = c, m = !0) : (d = k.toByteArray(c), m = !1);
            e = d.length;
            g = 0;
            for (f = e - 1; g < f && 0 > b[d[g]];) g++;
            for (; 0 < f && 0 > b[d[f]];) f--;
            l = "=" == d[f] ? "=" == d[f - 1] ? 2 : 1 : 0;
            a = f - g + 1;
            j = 76 < e ? ("\r" == d[76] ? a / 78 : 0) << 1 : 0;
            e = (6 * (a - j) >> 3) - l;
            a = Array(e);
            q = p = 0;
            for (eLen = 3 * (e / 3); p < eLen;) n = b[d[g++]] << 18 | b[d[g++]] <<
                12 | b[d[g++]] << 6 | b[d[g++]], a[p++] = n >> 16 & 255, a[p++] = n >> 8 & 255, a[p++] = n & 255, 0 < j && 19 == ++q && (g += 2, q = 0);
            if (p < e) {
                for (j = n = 0; g <= f - l; j++) n |= b[d[g++]] << 18 - 6 * j;
                for (b = 16; p < e; b -= 8) a[p++] = n >> b & 255
            }
            if (m) return a;
            for (n = 0; n < a.length; n++) a[n] = String.fromCharCode(a[n]);
            return a.join("")
        }
    };
    k.Base64.init();
    NBBY = 8;
    MATCH_BITS = 6;
    MATCH_MIN = 3;
    MATCH_MAX = (1 << MATCH_BITS) + (MATCH_MIN - 1);
    OFFSET_MASK = (1 << 16 - MATCH_BITS) - 1;
    LEMPEL_SIZE = 256;
    k.compress = function (c) {
        var h = [],
            b, a = 0,
            d = 0,
            e, m, g = 1 << NBBY - 1,
            f, l, j = Array(LEMPEL_SIZE);
        for (b = 0; b < LEMPEL_SIZE; b++) j[b] =
            3435973836;
        c = c.constructor == Array ? c : k.toByteArray(c);
        for (b = c.length; a < b;) {
            if ((g <<= 1) == 1 << NBBY) {
                if (d >= b - 1 - 2 * NBBY) {
                    f = b;
                    for (d = a = 0; f; f--) h[d++] = c[a++];
                    break
                }
                g = 1;
                m = d;
                h[d++] = 0
            }
            if (a > b - MATCH_MAX) h[d++] = c[a++];
            else if (e = (c[a] + 13 ^ c[a + 1] - 13 ^ c[a + 2]) & LEMPEL_SIZE - 1, l = a - j[e] & OFFSET_MASK, j[e] = a, e = a - l, 0 <= e && e != a && c[a] == c[e] && c[a + 1] == c[e + 1] && c[a + 2] == c[e + 2]) {
                h[m] |= g;
                for (f = MATCH_MIN; f < MATCH_MAX && c[a + f] == c[e + f]; f++);
                h[d++] = f - MATCH_MIN << NBBY - MATCH_BITS | l >> NBBY;
                h[d++] = l;
                a += f
            } else h[d++] = c[a++]
        }
        return h
    };
    k.decompress = function (c,
        h) {
        var b, a = [],
            d, e = 0,
            m = 0,
            g, f, l = 1 << NBBY - 1,
            j;
        b = c.constructor == Array ? c : k.toByteArray(c);
        for (d = b.length; e < d;) {
            if ((l <<= 1) == 1 << NBBY) l = 1, f = b[e++];
            if (f & l)
                if (j = (b[e] >> NBBY - MATCH_BITS) + MATCH_MIN, g = (b[e] << NBBY | b[e + 1]) & OFFSET_MASK, e += 2, 0 <= (g = m - g))
                    for (; 0 <= --j;) a[m++] = a[g++];
                else break;
                else a[m++] = b[e++]
        }
        if (!("undefined" == typeof h ? 0 : h)) {
            for (b = 0; b < m; b++) a[b] = String.fromCharCode(a[b]);
            a = a.join("")
        }
        return a
    }
})(fastcompressor);

如果没记错的话……下面是你如何使用它:

var compressed = fastcompressor.compress("0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"); // data less than this length poses issues.
var decompressed = fastcompressor.decompress(compressed);

Rgds....Hoonto/Matt

此外，我发布的内容经过缩小但经过美化，并且为了便于使用而略微做了调整。检查上面更新中的链接以获取原始内容。

关于javascript - 在javascript中压缩一个blob，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/17130387/