Question

我需要使用ajax将blob发送到服务器，但它最终会变得有点大，我想减少上传时间。我已经尝试过jszip了，但是这只是在zip中给了我一个空文件。我也尝试了btoa（），但事实证明编码值最终只是[object Blob]而不是实际的blob数据。压缩blob有哪些选择？

以下是我用于jszip的代码：

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

然后我将“content”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文件打开很好，但recording.wav是一个0长度的文件。

此外，我尝试使用here找到的LZW实现。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);

但是，解压缩会返回null。

Answer 1

警告：使用专门针对该类型数据的算法，可能更有效地压缩像音频文件之类的东西。但是，要知道如下所示找到合理的无损实现是多么困难，我非常担心在Javascript中很难找到满足您需求的特定数据类型的实现。

无论如何，我对Javascript中的压缩/解压缩也有这种普遍需求，我需要相同的算法来同时运行客户端（浏览器）和服务器端（node.js），我需要它处理非常大的文件。我检查了jszip，我还尝试了至少五到六个LZW算法，其中没有一个满足要求。我不记得每个具体的问题是什么，但足以说在javascript中找到一个兼容服务器和客户端并处理大文件的好的和FAST压缩器/解压缩器是非常困难的！我尝试了至少十几种不同的压缩算法实现，最后用这个算法解决了 - 它还没有让我失望！

<强>更新

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

由一个名叫熊的人 - 感谢贝尔，无论你是谁，你都是最好的。它是LZJB：http://en.wikipedia.org/wiki/LZJB

更新2

纠正了分号丢失的问题 - 不应再为对象提供功能错误。
此实现停止处理长度小于约80个字符的数据。所以我更新了示例来反映这一点。
实现了base64编码/解码方法实际上暴露在此版本传入的对象上，所以......

目前看看我们可以对特定的blob类型做些什么 - 例如最好的方法是图像与音频等，因为这对于一般的JS人来说是有用的...将在这里更新所发现的内容。 / LI>

更新3

Bear的原始Iuppiter源周围有一个比我下面发布的更好的包装器。它由cscott和github编写：https://github.com/cscott/lzjb

我将切换到这个，因为它也会流式传输。

以下是Node.js中与wav文件一起使用的示例。但在复制示例之前，让我先给你一个可怕的消息，至少对于我尝试过的这个wav文件：

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（并播放了它）。但是，压缩的一个似乎比原始大。好好拍。在任何情况下，尝试你的数据可能会很好，你永远不会知道，你可能会很幸运。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) {});

});

在一天结束时，我认为在大多数形式的二进制数据上实现任何级别的压缩都太难了，而这些二进制数据并没有被生成的base64编码所破坏。终端控制角色的日子一直困扰着我们。您可以尝试升级到不同的基础，但这也存在风险和问题。

请参阅此示例： What is the most efficient binary to text encoding?

这个： Why don't people use base128?

但有一件事，肯定在你接受答案之前，请在你的blob上尝试一下，我主要用它来压缩utf-8，我想确定它适用于你的具体数据。

无论如何，这是！

/**
$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);

如果记忆服务......这就是你如何使用它：

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

RGDS .... Hoonto /马特

另外，我发布的内容是缩小但美化，并且非常适合易用性。检查上面更新中的链接，了解原始内容。

Answer 2

JS Zip工作正常，只需更正您的语法..

function create_zip() {
    var zip = new JSZip();
    zip.add("recording.wav", blobfile);//here you have to give blobFile in the form of raw bits >> convert it in json notation.. or stream .. 
    zip.add("hello2.txt", "Hello Second World\n");//this is optional..
    content = zip.generate();
    location.href="data:application/zip;base64," + content;
}

你也可以添加多个文件..

只要zip.file将成为zip.add

然后zip.generate（）将完成其余的工作..正如您所做的那样，

或者参考old Post它的最后一部分JavaScript，如果你可以利用你可以忽略的使用Objective C的帖子用户记录，那么NativeBridge会很有用，但是你可以使用JavaScript和Socket发送这个对象/可以利用..

我希望这会...... ...）

在javascript中压缩blob

2 个答案: