Subtitles, audio tracks, and the three ways they go wrong
Subtitles fail in exactly three ways: they are not there at all, they are there but the letters are wrong, or they are there and correct but drifting away from the dialogue. Each has a different cause and a different fix, and none of them requires touching the video.
Subtitles live in one of two places
A subtitle track is either inside the video file or beside it. Inside means the container carries it as a separate track, exactly the way it carries the audio — an MKV can hold a dozen of them, in a dozen languages, and none of it affects the picture. Beside means a separate small text file, usually with the same name as the video and a .srt ending, that a player is expected to notice and load.
The difference matters more than it looks. An embedded track travels with the file forever: rename it, move it to another device, and the subtitles are still there. A separate file is easy to edit and easy to swap for a better translation, but it is also easy to lose, and it only gets picked up automatically if it is named to match and sitting in the same folder.
There is a third kind you will meet on discs and some broadcast recordings: bitmap subtitles (PGS or VOBSUB), which are not text at all but tiny images of text. They cannot be restyled, resized or searched, and a player has to draw them over the picture as-is. If your subtitles refuse to change size, this is why.
The formats you will actually run into
| Format | Kind | Styling | Notes |
|---|---|---|---|
| SRT (SubRip) | Text | Almost none | The universal one. Timestamps and lines, nothing else. Works everywhere. |
| ASS / SSA | Text | Full | Fonts, colours, positioning, karaoke. Standard for anime fansubs and any translation with signs. |
| WebVTT | Text | Some | The web standard, used by HLS streams and browser video. |
| SUB / IDX | Bitmap | None | From DVDs. Images of text, so it cannot be resized or restyled. |
| PGS | Bitmap | None | The Blu-ray equivalent. Same limitation, higher resolution. |
| CEA-608 / 708 | Text | Limited | Closed captions carried inside the video stream itself, common in broadcast recordings. |
Text formats can be restyled by the player — size, colour, background, position. Bitmap formats cannot, no matter what the player offers. That is a property of the subtitle, not a missing feature.
Why the accented letters turn into rubbish
You open a Turkish subtitle and see ç where ç should be, or a row of question marks, or a ? in the middle of every other word. Nothing is corrupted. The file is being read with the wrong character encoding.
A text file is bytes. An encoding is the agreement about which byte means which letter. Modern files use UTF-8, which covers every alphabet at once. Older subtitle files — and there are a great many of them, because subtitles circulate for decades — use a regional encoding instead: Windows-1254 for Turkish, Windows-1251 for Cyrillic, Windows-1250 for Central European, Shift-JIS for Japanese. Each of those maps the same byte to a different letter.
When a player assumes UTF-8 and the file is Windows-1254, every Turkish-specific character comes out wrong while plain ASCII letters look fine. That is the signature of an encoding mismatch: the sentence is readable but ı, ş, ğ, ç, ö and ü are broken. A player that lets you pick the encoding fixes it in one tap. A player that does not, cannot show that file correctly at all — and neither can converting the video, because the video was never the problem.
Fixing subtitles that do not match the dialogue
Out-of-sync subtitles come in two kinds, and telling them apart takes about thirty seconds. Work through this in order.
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Check the offset at the start of the film
Play the first line of dialogue and note whether the subtitle appears early or late, and by roughly how much. Anything under half a second is not worth chasing.
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Check the same thing near the end
Jump to the last ten minutes and compare again. This is the diagnostic step, and it is the one people skip.
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If the gap is the same at both ends, it is a constant offset
The subtitle file is simply shifted. Use the player’s subtitle delay control to nudge it forward or back until the first line lands, and the whole film will be right. This is the common case.
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If the gap grows as the film goes on, it is a frame-rate mismatch
The subtitles were timed against a 23.976 fps release and your video is 25 fps, or the reverse. A delay control cannot fix this — the drift accumulates. You need a subtitle file made for your release, or a desktop tool that rescales the timings.
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If the subtitles are right but the scenes are wrong, you have the wrong cut
Extended editions, theatrical cuts and broadcast versions differ by minutes. No amount of adjustment reconciles them; find the file that names the same cut as your video.
Embedded subtitle tracks are almost never out of sync, because whoever built the file timed them against that exact video. Sync problems are overwhelmingly a downloaded-.srt problem.
The same file, several languages
Audio tracks work exactly like subtitle tracks: a container can hold as many as it likes, and a player should let you switch between them without stopping.
Original and dubbed together
A typical release carries the original language plus one or two dubs. Switching mid-scene is the fastest way to decide which you would rather watch, and it costs nothing — both tracks were always in the file.
Commentary and descriptive audio
Director commentary and audio description tracks ride along in the same file. They are usually labelled, which is why a good player shows track names rather than “Track 1, Track 2”.
Surround versus stereo
Films often carry a 5.1 AC-3 or DTS track and a stereo AAC track. On headphones the stereo track is frequently the better choice — a 5.1 mix folded down can leave dialogue buried under effects.
Forced subtitles
A “forced” track only covers the parts spoken in another language — the alien dialogue, the foreign newspaper — rather than the whole film. If subtitles appear for two lines and vanish, that is what you selected.
Making subtitles comfortable to read
Small settings, large difference over a two-hour film.
- Size relative to the screen
What is readable on a Mac is too small on a phone held at arm’s length. Set it per device, not once.
- A background or outline
White text over a snow scene disappears. A thin black outline or a translucent band behind the text solves it without dominating the picture.
- Position above the black bar
On a wide film, dropping subtitles into the letterbox bar keeps them off the image entirely.
- One track, not two
If you have both an embedded track and a downloaded file loaded, you will get two overlapping lines. Turn one off.
Common questions
Why does my downloaded .srt not load automatically?
Automatic loading depends on the subtitle file having the same base name as the video and living in the same folder — Film.mkv and Film.srt. A name like Film.720p.tr.srt beside Film.mkv usually still works because most players match on the prefix, but subtitles(1).srt will not. Rename it, or load it by hand.
Can I get subtitles out of a video file?
Text tracks, yes — they can be extracted to a .srt without touching the video, and this is a remux operation, not a conversion. Bitmap tracks like PGS cannot become text without running OCR over them, which is a desktop job and never perfect.
Do subtitles make the file bigger?
Text subtitles are negligible — a full film is 40 to 80 kilobytes, which is nothing against several gigabytes of video. Bitmap subtitle tracks are actual images and can add tens of megabytes each, which is why disc rips with ten subtitle languages are noticeably larger.
Why can I not change the font of these subtitles?
They are bitmaps — PGS or VOBSUB, extracted from a disc. There is no text to restyle, only a picture of text. Look for a text-based track in the same file, or a separate .srt.
What FoxDL does with subtitles
Everything here is handled in the player, without a conversion step and without leaving playback.
- Every subtitle and audio track the file carries is listed by name and language, and switched while the film keeps playing.
- Text and bitmap tracks both render, including ASS/SSA styling where the file specifies it.
- Subtitle delay is adjustable during playback, which is the fix for the constant-offset case above.
- Character encoding can be chosen rather than assumed — the answer to Turkish, Cyrillic and Central European subtitles arriving as rubbish.
- Size, colour and background are yours to set, per the reading notes above.
Track selection and subtitle controls are part of the free version on iPhone, iPad and Mac.
Questions people ask about this
- How do I turn on subtitles and choose between them?
- Can I switch the audio track on a dual-audio file?
- How do I play MKV files on iPhone, iPad or Mac?
- Which video and audio formats does FoxDL play?
Keep reading
Why your iPhone opens one video file and refuses the next
Containers, codecs, and the three ways to watch a file iOS refuses to open.
Lossless, bitrate and the equalizer: what changes the sound and what does not
What lossless changes, what an equalizer really does, and what improves listening first.
What has to happen before a web page will give you its file
The four ways a page delivers video, and why only one of them is a file you can keep.
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