While a MHTML-encoded file contains portions that are pure HTML code, complications can occur when attempting to convert MHTML to HTML. Several programs are able to read MHTML — or Multipurpose Internet Mail Extensions (MIME) HyperText Markup Language (HTML) — files and derived formats, but a special type of program is required to convert and write the file’s contents to HTML. Problems could occur, because digital data from the website are encoded within the file and reconstructing the website with the correct links to all of the information locally can be a daunting task. Programs exist for most operating systems that allow MHTML to HTML conversions, although extra work might be required on the part of the user.
The primary issue for converting files from MHTML to HTML is the binary data that are written in the file. The data are saved in a way that allows the MHTML file to be read and displayed by a web browser but does not make it easy to convert that same file. MHTML is stored as a kind of embedded code that uses different variables to keep the locations of the digital files organized. The binary information, such as an image that is online, is stored on the original website with links to the online locations. This information is removed and translated into local variables with MHTML files, making it difficult to actually match up the binary media to its proper location and formatting within the HTML document.
Few programs are available that can convert MHTML to HTML. There are plug-ins and other add-ons that can allow a program to load, edit and then re-save the file back into MHTML, but there are only a handful of standalone programs that will attempt to convert it to HTML. Frequently, these programs require the user to look at the code to sort out where the binary files should be placed in the code, allowing them to reconstruct the page from the archive.
Not all web pages can be accurately saved as an MHTML file. A variety of complex formats that can be embedded as media on a website will not save properly, if at all. This includes Java® applets, streaming media and many scripts that rely on other files on the server to which the browsing computer has no access.
The most effective way to convert MHTML to HTML is to find standalone programs and plug-ins that will incrementally convert the files from one format to another and, finally, possibly to HTML. Certain operating systems do not even have support for MHTML files within their own browsers. Failing everything else, it is possible to manually decode the binary MIME information in the file by hand with a base 64 decoder, extract only the HTML and attempt to manually reconstruct the website held in the archive, but this process would be very labor intensive.