XHR2 is one part of the APIs required for my use case as that is the easiest way to download for example a music file. However, while downloading, there's no way to pipe the download(ing) blob to the HTML5 Audio element as to play Audio it requires an object URL, and an object URL can (currently) only point to a static Blob, as well as the fact that a Blob cannot be appended. This would be important for listening streaming audio that needs to be processed in JavaScript or cached to persistant storage using the Filesystem APIs without having to wait for the entire file to be downloaded into an ArrayBuffer or Blob.
I'm not really sure about the <device> tag fitting in with this as it seems to be more about reading serial ports and cameras from what I've seen, however any streaming interface that could be specified could be also used in the device API to stream binary content to devices. My suggestion was for another alternative version of Blob and/or createObjectUrl that mimicks how a HTTP request can be parsed and (in the case of audio or video) start playing before it has finished downloading (e.g. got to the content-length or had a connection close) by pushing content when it is appended to the blob and then the "virtual connection" can be closed when the Blob has finished being built by calling a close() function. I've also thought of other alternatives, but I'd make sure that there isn't already a way to do this with the current (specified) APIs, and I think this has the most other use cases as any data that takes a while to process can be streamed to the user or other parts of the browser. Thanks, -- Adam Malcontenti-Wilson On Sat, Jan 22, 2011 at 5:55 AM, David Flanagan <da...@davidflanagan.com> wrote: > Doesn't the current XHR2 spec address this use case? > Browsers don't seem to implement it yet, but shouldn't something like this > work for the original poster? > > x = new XMLHttpRequest() > x.open("GET", "http://my-media-file"); > x.responseType = "blob"; > x.send(); > var nbytes = 0; > x.onprogress = function(e) { > var blob = x.response.slice(nbytes, e.loaded-nbytes); > nbytes += blob.size; > var reader = new FileReader(); > reader.readAsArrayBuffer(blob, function() { > // process blob content here > }); > > } > > David Flanagan > > On 01/21/2011 02:02 AM, Jeremy Orlow wrote: >> >> Would something like this tie in to the<device> work that's being done >> maybe? >> >> ---------- Forwarded message ---------- >> From: Adam Malcontenti-Wilson<adman....@gmail.com> >> Date: Fri, Jan 21, 2011 at 6:21 AM >> Subject: [chromium-html5] File API Streaming Blobs >> To: Chromium HTML5<chromium-ht...@chromium.org> >> >> >> Hi. >> I'm trying to make an application which will download media files from >> a server and cache them locally, as well as playing them back but I'm >> trying to figure out how I could do so without making the user wait >> for the entire file to be downloaded, converted to a blob, then >> saved. >> >> For example, suppose that I create a new BlobBuilder, append "hello", >> get the Blob, and then create an object url from that blob, and then >> open the object url. Any other text that I append to the BlobBuilder >> would not go into the old blob that I created a url for, and hence not >> shown making "streaming" impossible. >> >> Is there any other methods in the spec(s) to implement such >> streaming? >> >> If not, perhaps there needs to be yet another object to have a way of >> creating a "StreamingBlob" that doesn't "close" the virtual connection >> to the browser until a close method is called, thereby facilitating >> streaming. >> >> Thanks, >> > > -- Adam Malcontenti-Wilson