Add preview for .mov files

[varkor]

Add preview for .mov files

[timabbott]

Here's the Zulip code around this:

    def is_video(self, url: str) -> bool:                                                                                                                                                                          
        if not self.zmd.image_preview_enabled:                                                                                                                                                                     
            return False                                                                                                                                                                                           
                                                                                                                                                                                                                   
        url_type = mimetypes.guess_type(url)[0]                                                                                                                                                                    
        # Support only video formats (containers) that are supported cross-browser and cross-device. As per                                                                                                        
        # https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Containers#index_of_media_container_formats_file_types                                                                                        
        # MP4 and WebM are the only formats that are widely supported.                                                                                                                                             
        supported_mimetypes = ["video/mp4", "video/webm"]                                                                                                                                                          
        return url_type in supported_mimetypes                                                                                                                                                                     

As detailed in https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Containers#index_of_media_container_formats_file_types, the .mov format isn't supported in some major browsers, like Firefox. (I haven't found a good resource on why Firefox doesn't support it, but I'm guessing it relates to Quicktime's history as a proprietary Apple technology).

There are other ways we could handle this -- re-encoding videos is a lot of CPU and not likely a great plan, but we could consider rendering the preview elements and just hiding them on browsers that don't support codecs like this... with the downside being that it'd just fail to work for Firefox users, without much hint to the person posting the message. It's worth some testing on what firefox does with a player element for an unsupported format.

Another direction would be to just communicate when you upload a .mov that we're not generating a preview because that format isn't widely supported by all browsers.