Video Monetization

How to Add Subtitles to MP4s in 5 Easy Steps (Video)

By Dann Albright
12 Min Read
How to add subtitles to MP4 videos

Adding subtitles to your videos files is a sure way to increase video shares by at least 15%. This is especially true for videos on social media, where over 80% of views are without sound.

No matter where you plan on posting your video, it’s a good idea to add subtitles. But it’s not always easy to figure out how to do that.

So we’ll walk you through how to add subtitles to MP4 files in five easy steps. If you’re more of a video-learner, we got you covered right here (if you’d rather read, keep scrolling):

Adding Subtitles to MP4s with Aegisub

Unless you want to manually create a very long text file that contains your subtitles, you’ll want to use an app that’s designed for adding subtitles to your MP4. We recommend Aegisub, a free and open-source tool that’s great for adding subtitles to videos on both Windows and Mac.

Working with Aegisub isn’t always intuitive, but once you get the hang of it, you’ll be able to add subtitles relatively quickly. We’ll walk you through the basics here to give you an idea of how to get started.

Start by heading to and downloading the app for your operating system.

1. Open Your Video

After the program’s been installed, open it and click Video > Open Video.

Select your video and hit Open.

You’ll now see the main subtitling interface:

Openning video in Aegisub

On the left, you’ll see the video you opened. On the right is the audio track. And at the bottom is the subtitle grid, which includes the start and end time, characters per second (CPS), styling, and the text of each subtitle.

2. Select the Audio for Subtitling

To get started, scroll the audio track to the first line you’d like to subtitle. You can either hit the Play button under the video or use the scroll bar under the audio track to find the first speech sounds in the spectrum analyzer.

Selecting the audio for the caption in Aegisub

You can also click the Spectrum Analyzer Mode button to change to a waveform view, if it’s helpful:

Using the spectrum analyzer in Aegisub

No matter which mode you use, click and drag to select the first phrase or sentence that you’d like to subtitle. Use the video and the spectrum analyzer to determine good starting and ending times for the subtitle.

Selecting the first phrase for the caption

To play the audio from your selection, hit the Spacebar or click the Play audio until the end of the selection is reached button (it’s the play button between blue brackets).

Adjust both ends of the selection until it covers the amount of time that you’d like your subtitle to be on the screen.

3. Enter Your Subtitles

Then click into the subtitle editor and type the words you’d like displayed on the screen:

Entering your caption in Aegisub

As you type, you’ll see two numbers going up. First, the number of characters in the longest line of the subtitle:

Length of the caption in Aegisub

Second, the CPS value in the subtitle grid below:

CPS value in Aegisub

If either of these boxes turns red, you may want to reconsider how you’re formatting your subtitle.

Too many characters per line make the viewer’s eye move far across the screen, which isn’t ideal. You can add a line break by pressing Shift + Enter to move some of your text onto the next line.

Adding line breaks to the caption

Note the “\N” in the line above; you can also type these characters for a line break.

If the CPS value is too high, you’re asking your readers to go through a lot of text in a short period of time. To fix this, you’ll need to split your text across two different subtitles (see below for an easy way to do this).

When you’re satisfied with the amount of text you have in the subtitle, hit Enter or click Commit any pending audio changes (the green check mark below the spectrum analyzer).

applying the changes in Aegisub

You’ll now see a subtitle in the subtitles grid, marked with the times that you’ve selected:

Subtitle grid view in Aegisub

If you need to tweak the times that the subtitle is displayed, just click the subtitle in the grid and change the start and end times in the subtitle editor below the audio track.

When you commit changes to a subtitle, Aegisub will create a new selection for you that you can then use for the next subtitle. If you need to manually create a new subtitle, just right-click in the subtitle grid and select Insert (before), Insert (after), Insert at video time (before), or Insert at video time (after).

Once you’ve created a subtitle, just repeat the process for the rest of the audio in your video. Be sure to play the whole video from time to time to make sure that your subtitles are timed well.

4. Save or Export Your Subtitles

When you’re done subtitling your MP4, you’ll want to save the subtitle file so you can use it later. Just click File > Save or the Save icon in the menu bar.

You’ll notice that your file is saved, by default, in the Advanced Substation Alpha (.ASS) format. This is a full-featured format, but might not be as widely accepted as the more common .SRT format (for example, you’ll need an SRT file to upload your subtitles to YouTube).

If you want to save your subtitles as an SRT file, just go to File > Export Subtitles and click Export on the resulting window. You can then save your file with any supported extension, including .SRT.

Exporting the subtitles from Aegisub

5. Encode Your Subtitles (Optional)

Once you’ve saved or exported your subtitles, they’re ready to be loaded in a media player. Many media players allow you to open a video file and select a separate subtitle file to be played with it.

This is convenient, as it means you can add subtitles without encoding. And that saves you time.

If you want to permanently add subtitles to your MP4 (often called “hard subbing”), though, you’ll need to encode them into the video. Note that if you hard sub your subtitles, there will never be an option to turn them off. They’ll be permanently displayed in that video file.

We like VLC for this, as it’s another free app that’s packed with useful features.

To hard code your subtitles into an MP4 file, open VLC and open the video with Media > Open File.

When you file is open, click Subtitle > Add Subtitle File:

Adding subtitle file to your video player of choice

Select your file, and VLC will load it.

Let the video play for a few moments to ensure that the subtitle file has been loaded correctly.

If everything looks alright, hit File > Convert/Save.

In the resulting window, click Add to select your video file:

Adding video file to VLC Player

Then make sure that Use a subtitle file is checked, and click Browse to select your subtitle file.

Selecting the subtitle file in VLC

Click Convert/Save, then enter a destination for your file and hit Start.

When VLC is done encoding, you’ll have an MP4 with hard-coded subtitles.

Tips for Easier Subtitling

There’s a huge number of options, shortcuts, workflows, and tools in Aegisub that make the subtitling process easier. And if you plan on doing a lot of subtitling, it will pay off to learn them.

But if you’re only going to use it occasionally, or for smaller projects, you don’t need to know everything. We’ve picked out a few useful things here that will help you add subtitles to your MP4s more efficiently.

Make the Audio Track Scroll with Video

With default settings, the audio track view doesn’t advance when the video is played. It can be very helpful to sync the two when you’re trying to find the best place to start and stop your subtitles.

Hit Alt + O to open Aegisub’s options, and click Audio in the left sidebar.

To make sure the video and audio track displays are always synced, select Lock scroll on the cursor.

Locking the scroll on cursor

Now, when you play the video, the audio track will scroll to keep up. This will help you figure out where the audio starts and stops while the video is playing.

Editing Subtitle Styles

Aegisub lets you apply all sorts of different styles to your subtitles. The default style is size 20 Arial font, in white, with black outlines and shadows.

To change that, click the Styles Manager button in the menu bar:

Editing the subtitle styles in Aegisub

In the Styles Manager, you’ll see a single script: Default. To edit your default style, select Default and click Edit.

Aegisub's style manager

In the resulting window, you can change fonts, sizes, colors, outlines, shadows, and alignments of your subtitles:

Aegisub's style editor

You can also use the Styles Manager to create new styles for use in your MP4.

After you’ve created a new style, you can apply it to any subtitle by selecting it in the style dropdown in the subtitle editor:

Applying style changes in Aegisub

Splitting Subtitles

When you select a section of audio and Aegisub tells you that you’ve put in too many characters, you’ll want to split your text over two different subtitles.

Instead of reselecting new timestamps, you can save yourself time by splitting the subtitle at a specific place. You’ll then have two subtitles that span the length of the original one.

First, advance the video to where you want the split to be.

Then right-click the subtitle you want to split and select Split lines before current frame or Split lines after current frame.

Split lines after current frame in Aegisub

The subtitle will be duplicated, so you’ll need to change the text in the resulting subtitles. But the timing will be perfect.

Using Hotkeys

Aegisub has a huge list of hotkeys and keyboard shortcuts. We’ve covered just a couple of the most useful here, but if you’re going to be spending a lot of time working on subtitles, you’ll want to get accustomed to using more of them.

To see the full list, open the Preferences window by pressing Alt + O, and click Interface > Hotkeys in the left sidebar.

Using Hotkeys in Aegisub

There are eight different categories of hotkeys, covering everything from saving and quitting to advancing the video one frame at a time. Look around to see what might be useful for you, or use the search bar at the top of the screen to find the hotkey you need.

Keep Practicing

Like any other powerful app, Aegisub has a lot of features that can make your life easier—but they can also be very intimidating. The best way to get used to the app and learn to use it more efficiently is to practice. It’s going to be frustrating at times, but you’ll get the hang of it.

You can also check out the Aegisub manual if you have a specific question.

Now that you know how to add subtitles to MP4 files, though, you’re ready to get started! Whether you’re uploading videos to YouTube or Facebook, making your own movies, or building a video course, you can now create, export, and encode your subtitles.