mpv Subtitle Font Too Small: How to Fix It

When the mpv subtitle font is too small or unexpectedly large, the cause is usually a subtitle size option, an active profile, an input binding, ASS styling, or display scaling. The media itself, hardware decoding, HDR processing, audio settings, yt-dlp, and network streaming rarely control subtitle font size directly. The safest approach is to reproduce the symptom without your normal configuration, identify whether the subtitle is plain text or ASS, and then change one relevant setting at a time.

1. Confirm the Symptom With a Minimal Clean mpv Command

Start by determining whether the subtitle size problem comes from mpv's defaults or from your configuration. The --no-config option tells mpv not to load normal configuration files, profiles, scripts, or user input bindings. This creates a useful baseline without requiring you to rename or delete anything.

1.1 Test a local file without your configuration

Open a terminal, Command Prompt, or PowerShell window and run mpv with a known local video:

mpv --no-config "path/to/video.mkv"

Use quotes around a path containing spaces. On Windows, a typical command might look like this:

mpv --no-config "C:\Videos\Example Movie.mkv"

On Linux or macOS, it might be:

mpv --no-config "/home/user/Videos/example.mkv"

Select the intended subtitle track if necessary. If the subtitle size looks normal during this test, mpv itself is working and the cause is probably in mpv.conf, an active profile, input.conf, or a script. Stop investigating GPU drivers, audio backends, and codecs at this point because the clean test has already isolated the problem to configuration.

If subtitles remain too small with --no-config, test a direct size value:

mpv --no-config --sub-font-size=55 "path/to/video.mkv"

You can try a larger value such as 65 or 75. Success means the displayed text changes to a comfortable size without affecting video scaling or playback. Once it does, stop increasing the value and make the successful setting persistent.

1.2 Identify the subtitle format

Plain-text subtitles such as SRT usually respond directly to sub-font-size. Styled ASS or SSA subtitles can contain their own font sizes, margins, positions, and animation instructions. In that case, mpv may preserve the embedded styling rather than applying your general subtitle preferences.

To see available tracks, press i or use mpv's statistics and track information overlays, depending on your bindings and mpv build. You can also run:

mpv --no-config --term-status-msg="${track-list}" "path/to/video.mkv"

For practical troubleshooting, compare the affected subtitle with a simple external SRT file. If SRT size changes correctly but an ASS track does not, the issue is ASS style precedence rather than general subtitle rendering.

2. Set the Correct Subtitle Font Size

2.1 Use the G and F keyboard shortcuts

mpv's default bindings use uppercase G to increase subtitle font size and uppercase F to decrease it. Uppercase means using Shift+G or Shift+F on a typical keyboard. Lowercase f normally toggles fullscreen, so the distinction matters.

Press uppercase G several times while a text subtitle is visible. If it grows, you have confirmed that the renderer and track are functioning. Press uppercase F if the subtitle is too large. Stop when the text is readable at your normal viewing distance.

These adjustments may not persist into a new mpv session. For a permanent result, place an explicit value in mpv.conf:

sub-font-size=65

If the shortcuts do nothing, check whether input.conf replaces the default bindings. User-defined bindings can override mpv's defaults. You can add explicit bindings such as:

G add sub-font-size 1
F add sub-font-size -1

Test these in a temporary configuration before adopting them permanently. Success means each key press produces a visible, incremental size change.

2.2 Find the active mpv.conf file

The location of mpv's configuration directory depends on the operating system and packaging method. Common locations include:

• %APPDATA%\mpv\mpv.conf on Windows
• ~/.config/mpv/mpv.conf on Linux
• ~/.config/mpv/mpv.conf on macOS when using the standard mpv configuration layout

Some Windows builds also support a portable portable_config directory beside the executable. A portable configuration can take precedence over the user configuration you expected mpv to load. Do not delete either directory. First identify which configuration is active by checking terminal output and testing a clearly recognizable temporary option.

Search every relevant configuration file for these terms:

• sub-font-size
• sub-scale
• sub-ass-override
• sub-scale-by-window
• sub-scale-with-window
• profile=

Remove duplicate size declarations or comment them out one at a time. In mpv configuration files, later or more specific settings can supersede earlier ones. Success means one documented sub-font-size setting produces the same result every time the same playback profile is used.

2.3 Check profile-specific subtitle styles

Profiles can make subtitles look correct for one file and wrong for another. For example, a fullscreen, HDR, streaming, or protocol-specific profile may contain a separate sub-font-size value. Auto profiles can activate according to filename, path, protocol, display, or other properties.

Review sections in mpv.conf that look like this:

[large-screen]
sub-font-size=75

Also look for commands that apply a profile at startup or through input.conf. Run mpv with:

mpv --show-profile=large-screen

Replace large-screen with the profile name you want to inspect. The output shows the options defined by that profile. If the wrong profile is responsible, correct its subtitle value or stop applying it to unrelated media. Do not compensate by adding progressively larger global values, because that can create the opposite problem elsewhere.

3. Understand ASS Override Limitations

ASS subtitles are designed to carry detailed presentation instructions. They may specify font families, point sizes, screen coordinates, borders, margins, colors, and per-line transformations. This is useful for carefully authored subtitles, but it means a general font-size preference may not override every element.

3.1 Test whether embedded ASS styling is responsible

Temporarily compare normal rendering with an ASS override mode:

mpv --no-config --sub-ass-override=force --sub-font-size=65 "path/to/video.mkv"

If the subtitle becomes readable only when forced overrides are enabled, the embedded ASS style is controlling its original appearance. However, forcing styles can damage intentional placement, signs, karaoke effects, overlapping dialogue, or typesetting. It should not automatically become a global setting.

A more careful approach is to use the override only for files that need it. Put it in a manually selected profile:

[readable-subs]
sub-ass-override=force
sub-font-size=65

Then launch mpv with:

mpv --profile=readable-subs "path/to/video.mkv"

Success means dialogue is comfortably sized and important ASS positioning remains acceptable. If signs, labels, or multiple speakers become misaligned, stop and return to the original ASS styling instead of forcing a global override.

3.2 Do not confuse track selection with font size

An audio or video track setting does not directly resize subtitles. A subtitle track setting can still matter if you accidentally select a different subtitle format. For example, one track might be plain SRT-style text while another is authored ASS with very small embedded text.

Use the track list to confirm the selected subtitle language, format, and source. Cycle subtitle tracks with the configured subtitle-cycle key, commonly j under default bindings, or select a track explicitly. If only one track is unusually small, treat it as a track-specific styling issue rather than changing every subtitle globally.

4. Check HiDPI Scaling and Window Behavior

Display scaling can make a technically correct subtitle size feel wrong. This is especially noticeable on 4K and other high-density displays, mixed-DPI multi-monitor systems, and small laptop screens.

4.1 Compare windowed and fullscreen playback

Play the same scene in a normal window, maximize the window, and then enter fullscreen. Observe whether the subtitle scales with the window or remains approximately the same physical size. Options related to scaling by or with the window can affect this behavior.

For a focused test, start with:

mpv --no-config --sub-font-size=65 "path/to/video.mkv"

Toggle fullscreen with lowercase f. If the subtitle is readable in fullscreen but too small in a compact window, decide which viewing mode matters most. Avoid chasing identical physical sizing across every window dimension unless that is an explicit requirement.

Success means the subtitle remains readable in your normal playback mode. Once the preferred windowed or fullscreen result is stable, stop changing unrelated video-output settings.

4.2 Account for operating system scaling

On Windows, verify the display's Scale setting, particularly when mpv moves between monitors with different scaling factors. On Linux, consider whether X11 or Wayland and the desktop's fractional-scaling configuration affect apparent UI and text size. On macOS, Retina scaling can similarly change the relationship between logical and physical pixels.

Before editing mpv, move the player to the monitor where it is normally used and restart it there. Then test sub-font-size. If only one display produces the problem, create a deliberate profile for that display workflow rather than making a global value extreme.

GPU drivers, video output drivers, shaders, HDR tone mapping, and hardware decoding can affect video presentation, performance, and color. They generally do not determine the requested subtitle font size. Investigate them only if subtitles are corrupted, missing, clipped, or rendered at the wrong resolution alongside broader display problems.

5. Use Logs and Runtime Information to Find Overrides

5.1 Capture a useful mpv log

If the clean test works but normal playback does not, generate a log from the failing launch:

mpv --log-file=mpv.log --msg-level=all=v "path/to/video.mkv"

Then repeat with --no-config and a different log filename:

mpv --no-config --log-file=mpv-clean.log --msg-level=all=v "path/to/video.mkv"

Compare the logs for loaded configuration files, scripts, profiles, subtitle tracks, and command-line options. Logs can be verbose, so search for config, profile, script, sub, and the affected file's subtitle format.

A successful diagnosis identifies a specific difference between normal and clean playback. Stop once that difference explains the size change. There is no benefit in fixing harmless audio, HDR, network, or decoder messages when subtitle rendering already works.

5.2 Check scripts and IPC clients

Lua or JavaScript extensions can issue runtime commands that alter subtitle properties. External front ends and IPC clients can do the same. Temporarily disable scripts without deleting them by using a clean --no-config test, or construct a separate temporary configuration directory containing only the setting under investigation.

If size changes a few seconds after playback starts, after switching tracks, or after entering fullscreen, a script, profile, or IPC command is especially plausible. Review scripts that manage subtitles, profiles, display modes, or playback state. Success means the chosen size remains stable throughout startup, track changes, seeking, and fullscreen transitions.

6. Rule Out Unrelated Playback Components

Users with advanced mpv setups often have hardware decoding, shaders, HDR profiles, yt-dlp integration, network streams, and custom screenshot settings. These components may appear in the same configuration but normally do not control subtitle font size.

• Hardware decoding: Changing hwdec is unnecessary when video and subtitles render correctly apart from text size.
• HDR and shaders: These affect video color or image processing, not the requested subtitle font size.
• Audio backend: Audio device selection cannot make subtitle text smaller.
• yt-dlp: It can affect online media and subtitle acquisition, but an already loaded text subtitle is sized by mpv and its renderer.
• Stream URL: A service may supply a differently styled subtitle track, but the URL itself does not set mpv's global font size.
• Screenshots: Screenshot options can determine whether subtitles appear in captures, but they do not normally change on-screen subtitle size.

If an online URL has tiny subtitles, test the same stream with --no-config and inspect which subtitle track is loaded. If no subtitle appears, that is a track availability or retrieval problem, not a font-size problem. Keep those diagnoses separate.

7. Run a Clean Temporary Test Before Making Permanent Changes

Use a controlled test sequence so you do not create conflicting fixes:

1. Run the file with --no-config.
2. Add only --sub-font-size=65.
3. If the file uses ASS and does not respond, temporarily add --sub-ass-override=force.
4. Compare windowed and fullscreen playback.
5. Repeat with your normal configuration.
6. Inspect profiles, input bindings, and scripts only after identifying where behavior changes.
7. Copy the smallest successful change into the correct configuration or profile.

Do not change font size, video output, hardware decoding, display scaling, shaders, and scripts simultaneously. Multiple changes make it difficult to know which one worked and may introduce a new mpv player issue.

The final success condition is simple: the intended subtitle track is readable at your normal viewing distance, remains consistent during typical playback, and does not require unrelated playback changes. Once that condition is met, stop troubleshooting.

8. Quick Fix Checklist

• Press uppercase G to enlarge subtitles or uppercase F to reduce them.
• Test with mpv --no-config "file".
• Try --sub-font-size=65 and adjust gradually.
• Add the successful value to the active mpv.conf.
• Search for duplicate settings in profiles and portable configuration directories.
• Check whether input.conf has replaced the G and F bindings.
• Identify whether the affected track is SRT, ASS, or SSA.
• Use sub-ass-override=force only as a careful, file-specific test.
• Compare fullscreen and windowed playback on the intended monitor.
• Use a log to identify loaded profiles, scripts, and configuration files.

9. Frequently Asked Questions

9.1 How do I permanently increase subtitle size in mpv?

Add a line such as sub-font-size=65 to the active mpv.conf. Adjust the number to suit your display and viewing distance. Confirm the value in both windowed and fullscreen playback before keeping it.

9.2 Why does sub-font-size work for SRT but not ASS?

ASS subtitles can contain their own style and size instructions. mpv may preserve those instructions. A temporary sub-ass-override=force test can confirm the cause, but forced styling may disrupt intentional positioning and should be used selectively.

9.3 Why do G and F not change subtitle size?

Use uppercase G and uppercase F, normally entered with Shift. If they still do nothing, a custom input.conf, script, front end, or IPC client may have replaced the default bindings. The selected subtitle may also be an ASS track whose styling limits the visible effect.

9.4 Why are subtitles a different size in fullscreen?

The apparent size can change because subtitles interact with window dimensions, video scaling, display resolution, and HiDPI behavior. Test on the intended monitor and tune the size for the playback mode you normally use. Review subtitle window-scaling options if the difference is excessive.

9.5 Can hardware decoding or HDR make subtitles too small?

Not normally. Hardware decoding and HDR processing primarily affect video decoding and presentation. If only subtitle size is wrong, begin with subtitle options, ASS styling, profiles, and display scaling. Change GPU-related settings only when there are broader rendering symptoms.

9.6 Should I delete my mpv configuration folder?

No. Use --no-config to test safely without loading it. If the clean test works, inspect individual files, profiles, scripts, and bindings. Preserve the original folder and change one item at a time.