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    <p>From <a href="https://wiki.mozilla.org/Audio_Data_API" rel="nofollow">https://wiki.mozilla.org/Audio_Data_API</a></p> <p>The data you're looking for is in the framebuffer property of the event object passed to your listener function</p> <p>To access a particular section of historical data, simply cache previous framebuffer captures yourself</p> <pre><code>var channels, rate, frameBufferLength, samples; function audioInfo() { var audio = document.getElementById('audio'); // After loadedmetadata event, following media element attributes are known: channels = audio.mozChannels; rate = audio.mozSampleRate; frameBufferLength = audio.mozFrameBufferLength; } function audioAvailable(event) { var samples = event.frameBuffer; var time = event.time; for (var i = 0; i &lt; frameBufferLength; i++) { // Do something with the audio data as it is played. processSample(samples[i], channels, rate); } } </code></pre> <p>ADDENDUM:</p> <p>OK, so you need your program to look into the future. As far as I know, this isn't doable unless you can use some kind of clever preload solution (although I suspect this won't work either - perhaps a subscription to the moz mailing list may enable you to request this as a future feature).</p> <p>I still don't know what exactly it is you're trying to do, but I have an HTML5 player that uses a drawn waveform background and draws an oscilloscope during playback using RAW audio data which I rip from the audio file myself on the server - I don't use the mozilla API because I want it to work in all ogg-supporting browsers, so I load a separate data blob altogether. This of course means a) it is not pure HTML5 and Javascript, and b) my player only plays files that originate from my server. In any case, the stages are:</p> <p>1) Use a command-line utility (I recommend sox) to extract the RAW data - I downmix it to mono, 8-bit 1khz PCM which is relatively small yet high enough resolution to be useful (1kb/sec). If you want to keep it (to draw an oscilloscope during playback in non-mozilla browsers) cache it in a database as a blob.</p> <p>2) Use the RAW PCM to draw a PNG of the wave using php_gd, and cache that (for your player background)</p> <p>3) if using the RAW data then you can load it into javascript as a base64-encoded string</p> <p>It is not impossible for you to do this even with external audio files if you use your server simply as a proxy to extract the RAW data, but then you will need to take care of the security issues that introduces.</p> <p>If this applies to you at all then let me know and I'll post some source code for these. The program in question will be released as an open source project at <a href="http://jukenix.org" rel="nofollow">http://jukenix.org</a> as soon as I've tidied it up a bit.</p> <p>P.S. screenshot of this in action is at bottom of page of link above</p>
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    1. POAudio data preprocessing using <audio> tag and Javascript
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    1. COThanks, 1360050. Your answer is helpful, but haven't solved my problem. Please see the UPDATE above, which may have described my problem more clearly. Thx.
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    2. COThanks Clancy. I believe your solution works. I have already thought about some solutions like yours, but a pure HTML5 solution would better meet my requirements. Perhaps I can find some wave decoders written in Javascript which might help me more.
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    3. COYes you will, but one way or another if you intend to use javascript to read an audio wave that originates in a binary audio file then you will have to convert the binary data yourself into something more grokkable. As far as I know, the mozilla Audio Data API is the only thing close to a solution which skips creating a separate RAW stream yourself, and as you say it only knows the state of the buffer. If you solve your problem, I'd be very interested to know what you decided.
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