Can't download mp4 files.

Sorry about the lack of info that I provided. Once you've clicked the link, on the left hand side, click "puntate integrali", which essentially means complete episodes. That takes you to another web page with pictures of several downloadable video files. If you click on one of the pictures, it should begin to play that particular video. Beneath the playing video, you may click "download" which normally triggers the file download process. It is at that stage that I am getting the error message, "quicktime player can't open mp4."

Unfortunately, you original URL is no longer valid and currently a 404 error is issued when I try to use it. The first random file i selected from the video news page returned an "not supported" error message so the files may be posted using different formats which can create additional problems. In any case, since I could not locate the original starting page, I could not follow your expanded instructions. As to the original error message, on my system it appears as soon as the targeted file is downloaded and QT attempts to open it. I suggest you go to the download folder and look at the downloaded file. If it shows just the generic MP4 icon (i.e., no preview option) and the files are extremely small (i.e., on the order of just a few hundred kilobytes, then it is not a standalone file but simply a "Reference" file which does not contain the data needed for playback and is not supported by either QT X or QT 7 players at this time—at least for the file(s) I tried. I did, however, manage to use an updated version of a third-party iTube downloader to create a file that was 1.2 GBs in size and probably represents the TV show episode I used for testing. Unfortunately, the atoms in the file will not parse correctly and so it is also incompatible QT X, QT 7, VLC, MPlayerX, or NicePlayer apps. Whether the atom problem is caused by the downloader or is a problem in source video file is, as yet, still unresolved.

I.e., the downloaded "standalone (?)" file looks like this:

While a normal MP4 file would look more like this:

I'm afraid that your level of expertise is beyond my own tech abilities. Are you saying if effect that the website has modified its programming routines to prevent my downloading of their files? I agree with you about not downloading files that can be viewed in real time in a browser, but I travel a fair amount and for instance on airplanes I enjoy watching these video files while I am not in a wireless environment.

I am saying the the files I was able to download were not compatible with any media player app I normally use.

It's an Italian website: http://www.rai.tv/dl/RaiTV/programmi/page/Page-b4d2014a-1ae4-4bdf-bf31-4f7261853 b0e.html.

The URL Reference provided is for a page of photo images. Since you did not provide a specific video URL, I picked one at random. The video I picked is a Flash MP4 video playing correctly in the Flash player plug-in under Safari. Unfortunately, you did not indicate how you are downloading MP4 files. Using the web page "download" button o nly downloads a "reference" MP4 file—not the actual standalone data file. Since the download file is not coded with a valid URL pointing to the stored video data, QT cannot "open" the file. I therefore tried a couple of specialized apps that download Tube-like site files based on the playing webpage URL reference. Neither of these apps were able to downloand the files. At this point my basic assumption is that the source web site has modified the source URL access programming routines and since the source data cannot be accessed at the moment by the means I normally use, the video data cannot be saved locally to your system. Since previous files were downloaded and stored prior to a probably change in the web site programming, they're not affected by this problem unless you try to re-download the content.

Strange but frustrating.

Hardly. Web sites frequently update their method of posting/playing content to keep up with browser changes and media handlng routines, as well as, prevent the wholesale downloading of content or unauthorized playback of files. You can, of course, still capture the video content during playback in the browser. I personally don't think its worth the file space to down load or capture files that can be freely viewed in a browser without wasting my personal storage space which is once again becoming critical for one of my RAID units.

through which service/website are you trying to download the mp4?