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I was trying to upload a JPEG file using chunked uploads. It is 270 MB (283,562,965 bytes) and 24576 x 29696 (730 megapixels / 729808896 pixels). The file was created using ImageMagick 6.7.9-8 2012-09-22 Q16 ("convert a.tiff a.jpg"). As soon as I try to upload it fails immediately at:

Error: http://bits.wikimedia.org/static-1.20wmf12/extensions/UploadWizard/resources/mw.UploadWizardUpload.js at line 471: NS_ERROR_FAILURE: Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMFileReader.result]

 if( this.file.type === 'image/jpeg' ) {
     var binReader = new FileReader();
     binReader.onload = function() {
         var binStr;
         if ( typeof binReader.result == 'string' ) {
>            binStr = binReader.result;
         } else {

Debugging in Firebug shows that binReader.result is undefined at the time of failure.

binReader FileReader {readyState=2,onload=[xpconnect wrapped nsIDOMEventListener],EMPTY=0, more...}
   DONE=2,
   EMPTY=0,	
   LOADING=1,
   error=null,
   onloadend=null,
   readyState=2,
   result=undefined,
   constructor=[object FileReader],
   abort=abort(),
   addEventListener=addEventListener(),
   dispatchEvent=dispatchEvent(),
   getInterface=getInterface(),
   readAsArrayBuffer=readAsArrayBuffer(),
   readAsBinaryString=readAsBinaryString(),
   readAsDataURL=readAsDataURL(),
   readAsText=readAsText(),
   removeEventListener=removeEventListener(),
   __proto__=[xpconnect wrapped native prototype] { ... }

I got the same failure in Chrome and Firefox. IE apparently has no chunked uploads support at all, as I'm unable to upload any file in it, it just claims to be uploading but uses no bandwidth.

I have no trouble uploading a smaller 90 MB JPEG file.