Computing: Computer Basics

Multimedia: MP4 and WebM - What are they, and how to convert them?

I guess that most video files, that you have locally stored on your computer are MP4 files. This is the most used format on video download sites. However, you may also find the videos in other formats. Lots of files on YouTube are available as both MP4 and WebM. What are these two file formats, what are their advantages and disadvantages, how can we convert a video from WebM to MP4?

MP4 (MPEG-4 Part 14), is a container format that follows ISO/IEC standards for storing audio and videos. It can also store other data like images and subtitles. MP4 is extremely popular and finds use in almost all modern-day use cases. It is an almost ubiquitous file format and can be run on any browser, platform, device, etc. Further, MP4 videos can also be easily streamed, shared, and transmitted over the Internet.

WebM is a media file format that was introduced in 2010 by Google. It is open-source and 100% free. The file structure of WebM format is based on the Matroska container, which allows it to support amazing video qualities. WebM was designed specifically for the web and is one of the more prominent video standards supported in HTML5. All the modern browsers support the WebM format. You can use the WebM video format to upload your digital videos to YouTube. WebM is also compatible with ooVoo, Skype, etc.

The previous paragraphs, as most of the comparison below, are based on the article WebM vs MP4 - Detailed Comparison, published by Pratik Wadgaonkar at Gumlet, that contains a lots more detailed description of the two file formats than this text.

MP4 vs WebM - Comparison details.

Video quality depends on the codecs used, so both MP4 and WebM may be better or less good quality. Due to the important video quality improvement obtained by the actual H.264 codec (used with MP4), we can however say that WebM tends to be slightly inferior compared to the output video quality of the MP4 format.

Both WebM and MP4 follow video compression that compresses the original files to a relatively small file size. Globally, the size of WebM videos is slightly smaller compared to MP4.

Platforms Compatibility. MP4 videos are highly compatible and can be viewed easily on any device, including handheld devices, laptops, PCs, etc. It is also compatible with the most popular browsers, such as Firefox, Chrome, Edge, Safari, and Opera. WebM format was essentially created for web use, and it does perfectly well at that, including in terms of compatibility. Whereas PC video players like VLC player fully support WebM files, WebM is not that well supported with handheld and mobile devices.

Some advantages of MP4:

• MP4 easily allows to integrate closed caption file formats, that are used to display video subtitles (WebM files cannot include these subtitles).
• The quality and file size offered by MP4 is totally adequate for video streaming over the Internet. Most video-sharing platforms encourage users to use the MP4 format (WebM is well supported by Wikimedia and YouTube, but may not be on the sharing platform that you would like to use).
• Both MP4 and WebM files are may be displayed as thumbnails in Windows 10/11 File Explorer (WebM thumbnails may not be supported on other platforms?). However, whereas editing the video tags (title, genre, release date, etc) may be easily done in the file Properties settings in Windows File Explorer, you'll need some special third party software to edit the tags of WebM files.

Some advantages of WebM:

• WebM is open source (what is not the case of MP4) and is totally compatible with HTML5.
• WebM is easier to use with video editing software than MP4 (MP4 videos tend to cause many video software crashes). This makes WebM the favorite file format for video editing tools.

So, what conclusion should we draw out of this? I personally would say, that

• If you need to edit your videos, use WebM.
• To upload videos to a sharing platform, you may normally use either of the two formats. However, be aware that not all sharing platforms support WebM, and that WebM file playback is not well supported on handheld and mobile devices.
• To store video files on your computer, you should use MP4. This allows you to easily tag your movie files. It also allows to store movies with subtitles in a language that you understand. If free space on your local disk is a serious issue, using WebM could be helpful...

Converting WebM videos to MP4.

I store all my videos using the MP4 format in order to be able to easily tag them; also, I have lots of Asian movies, that without English subtitles would be rather worthless for me. Most videos on the net are provided as MP4, however, sometimes you only find the movie as WebM file. So, how can we do to convert the downloaded WebM file into an MP4 file to store into the video library?

VLC Player is one of those pieces of software, that I personally call "must have" (cf. my Personal software review: VLC player article). If you don't care about disk space, you can use VLC to do the conversion of your WebM file to MP4. If I say "if you don't care about disk space", it's because the file created by VLC Player is rather big, possibly some three times bigger than the original file (at least, that's how it was when I used VLC Player to do the conversion; and by changing the output settings, I did not succeed to create a smaller MP4).

To convert a file in VLC Player, choose Media > Convert/Save from the menu bar. The Open Media dialog box opens; push the Add button. Then, at the bottom of the dialog box, expand the drop-down list, and choose Convert.

The Convert dialog box opens. From the drop-down list at the right of "Profiles", select Video for MPEG4 720p TV/device. This will create a 1280×720 pixels video. If the destination file path isn't filled in automatically, do it manually in this dialog box.

Converting a video is a very complicated process. Thus, it will need time (and lots of system resources).

The screenshot below shows the audio and video properties of the new file. Note, that I set the MP4 tags before taking the screenshot (before setting the tags, you would probably want to remove the "Date created" property set by VLC).

So, if you have VLC Player installed (what you should...), the conversion of a WebM to an MP4 file is not a big deal. The problem is the file size of the MP4 created. Starting with a WebM file of 311 MB, I ended up with an MP4 file of more than 1 GB! Editing the conversion profile, choosing a smaller frame size did not help. I effectively got a smaller video, but the file size was the same as before (?).

To create a smaller file (smaller video with reduced quality), using the free software HandBrake is mostly a better choice compared to VLC Player. For details, please, have a look at my tutorial Reducing the file size of an MP4 video. Converting the WebM file to a "Fast 480p30" MP4 file is done exactly the same way than the MP4 to smaller MP4 conversion described in that text.

The screenshot below shows the conversion of our WebM file in HandBrake.

And here are the audio and video properties of the MP4 file. With a framesize of 538×360 pixels, the video quality is of course largely below "high definition". But, to look the movie on a PC, it's ok (at least for me). The file size (587 MB) is largely smaller than the one created by VLC Player, even though it's still bigger than the original WebM file.

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