在我的网页上,标签内有一个音频文件。
<!DOCTYPE html>
<html>
<audio src="myTrack.mp3" controls preload="auto"></audio>
</html>
我想将该标签中存储的文件切成多个10秒的音频文件,然后将它们作为自己的音频文件插入单独的<audio>
标签中,然后插入网页中。
是否可以在javascript中执行此操作?
是的,当然可以!:)
ArrayBuffer
并使用解码AudioContext
revokeObjectURL()
)。一个缺点是,当然,您必须在处理文件之前将整个文件加载到内存中。
希望我用于演示的文件可以通过当前的CDN来获得,该CDN用于允许CORS使用(我拥有版权,可以随时将其用于测试,但只能进行测试!:))。加载和解码可能需要一些时间,具体取决于您的系统和连接,因此请耐心等待...
理想情况下,您应该使用异步方法来分割缓冲区,但是该演示仅针对所需的步骤,以使缓冲区段可作为新文件片段使用。
还要注意,我没有考虑到最后一个段比其他段短(我使用floor,您应该使用ceil来计算段数并缩短最后一个块的长度)。我将其留给读者作为练习。
var actx = new(AudioContext || webkitAudioContext)(),
url = "//dl.dropboxusercontent.com/s/7ttdz6xsoaqbzdl/war_demo.mp3";
// STEP 1: Load audio file using AJAX ----------------------------------
fetch(url).then(function(resp) {return resp.arrayBuffer()}).then(decode);
// STEP 2: Decode the audio file ---------------------------------------
function decode(buffer) {
actx.decodeAudioData(buffer, split);
}
// STEP 3: Split the buffer --------------------------------------------
function split(abuffer) {
// calc number of segments and segment length
var channels = abuffer.numberOfChannels,
duration = abuffer.duration,
rate = abuffer.sampleRate,
segmentLen = 10,
count = Math.floor(duration / segmentLen),
offset = 0,
block = 10 * rate;
while(count--) {
var url = URL.createObjectURL(bufferToWave(abuffer, offset, block));
var audio = new Audio(url);
audio.controls = true;
audio.volume = 0.75;
document.body.appendChild(audio);
offset += block;
}
}
// Convert a audio-buffer segment to a Blob using WAVE representation
function bufferToWave(abuffer, offset, len) {
var numOfChan = abuffer.numberOfChannels,
length = len * numOfChan * 2 + 44,
buffer = new ArrayBuffer(length),
view = new DataView(buffer),
channels = [], i, sample,
pos = 0;
// write WAVE header
setUint32(0x46464952); // "RIFF"
setUint32(length - 8); // file length - 8
setUint32(0x45564157); // "WAVE"
setUint32(0x20746d66); // "fmt " chunk
setUint32(16); // length = 16
setUint16(1); // PCM (uncompressed)
setUint16(numOfChan);
setUint32(abuffer.sampleRate);
setUint32(abuffer.sampleRate * 2 * numOfChan); // avg. bytes/sec
setUint16(numOfChan * 2); // block-align
setUint16(16); // 16-bit (hardcoded in this demo)
setUint32(0x61746164); // "data" - chunk
setUint32(length - pos - 4); // chunk length
// write interleaved data
for(i = 0; i < abuffer.numberOfChannels; i++)
channels.push(abuffer.getChannelData(i));
while(pos < length) {
for(i = 0; i < numOfChan; i++) { // interleave channels
sample = Math.max(-1, Math.min(1, channels[i][offset])); // clamp
sample = (0.5 + sample < 0 ? sample * 32768 : sample * 32767)|0; // scale to 16-bit signed int
view.setInt16(pos, sample, true); // update data chunk
pos += 2;
}
offset++ // next source sample
}
// create Blob
return new Blob([buffer], {type: "audio/wav"});
function setUint16(data) {
view.setUint16(pos, data, true);
pos += 2;
}
function setUint32(data) {
view.setUint32(pos, data, true);
pos += 4;
}
}
audio {display:block;margin-bottom:1px}
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