We all know not to click on those shifty-looking attachments in emails, or to download files from dubious websites, but as file delivery of media increases, should we be worried about viruses in media files? In the case of the common computer virus, the answer is “probably not” – the structure of media files and applications used to parse or open MXF, QuickTime and other files do not make “good” hosts for this type of virus. Compared to an executable or any kind of XML-based file, media files are very specific in their structure and purpose – only containing metadata, video and audio – with any element labeled appropriately sent to the applicable decoder. Any labels that are not understood or supported by the parser are simply ignored.

However, this behavior of ignoring unsupported or unrecognized labels facilitates the existence of “dark metadata,” and this is a potential area of weakness in the broadcast chain. Dark metadata isn’t necessarily as menacing as the name could suggest and is most commonly used by media equipment and software vendors to store proprietary metadata that can be used downstream to inform dynamic processes – for example, to change the aspect ratio conversion mode during up or down conversion, or audio routing in a playout video server. When you know what dark metadata you have, where it is and what it means, it can add value to the workflow chain.

Since dark metadata will usually be ignored by parsers that don’t understand/support the proprietary data it carries, it can also be passed through the media lifecycle in a completely harmless way. However, if you are not aware of the existence of dark metadata and/or the values of the data it carries, then there is a risk that processes in the media path could be modified or activated unintentionally and unexpectedly. In this case, the media is in some way carrying a virus and in the worst case, could result in lost revenue.

The anti-virus software installed on your home or work PC isn’t going to be much help in this instance, but there are simple steps that can be taken to ensure that you don’t fall foul of “unknown unknowns.” 

• Implement a “normalization” stage at the entry point for media into your workflow. You can read other articles in this blog about the benefits of using a mezzanine file format, but even if files are delivered in the same format you use in-house, a simple re-wrapping process to “clean” and normalize the files can be a very lightweight process that adds little or no latency into the workflow.
• Talk to your suppliers and vendors to make sure you’re aware of any proprietary metadata that may be being passed into your workflow.
• If you have an automated file-QC tool, check whether it has a “dark metadata” test and switch it on – unless you definitely use proprietary metadata in your workflow, this won’t generate false positives and shouldn’t add any significant length to the test plan.

We’ll be looking at some of the other security concerns in future blogs, but as long as you know your dark metadata, there’s little risk of viral infection from media files.