Three kinds, and why it matters
What you can do with subtitles depends entirely on how they were delivered.
Burned-in
The text is part of the video image, painted in before broadcast. Nothing can remove, move or restyle it, because to the player it is simply picture. Common on international feeds and some sports coverage.
Bitmap
Delivered as small images overlaid on the video. They can be switched on and off, but not restyled — size, font and colour were decided when the images were made. Standard on broadcast television.
Text
Delivered as actual characters with timing information. These can be switched off, resized, recoloured and repositioned, because the player is drawing them. Common on on-demand content.
So "why can I not make the subtitles bigger" usually has the answer: because they are bitmap or burned-in, and there is no text to enlarge.
The format names you will actually see
Player menus and stream information panels name the formats rather than the categories above. These are the ones that turn up, and which of the three kinds each belongs to.
On live channels
- DVB subtitles — bitmap. The broadcast standard across Europe. Switchable, never restylable.
- Teletext subtitles — the older system behind the page 888 habit. Still carried on some feeds, and some players list it as a separate track from DVB.
- CEA-608 and CEA-708 — closed captions carried inside the video rather than as their own track, mostly on North American feeds. This is the usual reason a channel appears to have no subtitles in one player and perfectly good ones in another: support for reading them varies far more than support for DVB.
On the on-demand library
- SRT — plain text with timings, and the most common format you will meet. Fully restylable.
- ASS and SSA — text, but with styling written into the file itself: fonts, colours and screen positions. Restylable only up to a point, because the file's own instructions can override what you set in the player.
- WebVTT — the format used by web and HLS delivery. Behaves much like SRT.
If a player shows you a stream information overlay, it will normally name the subtitle format there, which settles the question of what is possible before you spend time in the settings. Our note on reading the stream info overlay covers where to find it.
Matching symptom to format
- They cannot be turned off at all — burned-in.
- They turn off but styling options do nothing — bitmap.
- Styling works — text.
- They vanish when the picture is cropped — the subtitles sit at the edge and a zoom setting is cutting them off. See aspect ratio and zoom problems.
- Nothing available on any channel — either the player is not requesting them, or the feeds do not carry them.
Why live and on-demand differ
Live subtitles are produced as the programme airs, often by a person keying them in, which is why they lag behind speech and contain errors. There is no opportunity to correct them.
On-demand subtitles are prepared in advance from a script, so they are more accurate and better timed. They are also more often text-format, which is why the styling controls that do nothing on live channels suddenly work in the library.
If subtitles matter to you, this is worth knowing before judging a service: the two halves genuinely behave differently, for reasons covered in live TV and on-demand.
What the player controls
Most players offer a subtitle menu during playback listing available tracks. A few things worth knowing:
- Tracks are labelled by language, and labels are sometimes wrong or missing. Trying each is often quicker than reading the list.
- "Off" may not appear if the only subtitles are burned in — there is nothing to switch.
- A delay or offset control exists in some players, which helps when text-format subtitles drift out of time. It cannot help with bitmap or burned-in.
- Preferred language settings save selecting a track each time, where the feeds label their tracks correctly.
Players differ considerably here; our comparison of IPTV players covers which handle subtitles well.
What cannot be fixed
Worth being direct about, because time gets spent on it.
Burned-in subtitles cannot be removed. A channel that carries no subtitle track cannot be made to produce one. Bitmap subtitles cannot be resized. And live subtitles will always lag the audio, because they are being written as people speak.
If subtitles are essential for a particular channel, the practical answer is usually to look for an alternative version of that channel in the line-up, since different feeds of the same channel sometimes differ in what they carry.
Frequently asked questions
Why can I not turn off the subtitles on some channels?
Because they are burned into the video image rather than delivered as a separate track. To the player they are part of the picture, so there is nothing to switch off.
Why can I not make IPTV subtitles bigger?
Because they are bitmap subtitles, delivered as small images with size and font already fixed. Only text-format subtitles, more common on on-demand content, can be restyled.
Why are live subtitles late and full of errors?
They are produced in real time as the programme airs, often typed by a person. On-demand subtitles are prepared in advance from a script, which is why they are more accurate.
My subtitles are cut off at the bottom of the screen. Why?
The picture is being cropped by a zoom setting or overscan, pushing the subtitle area off screen. Setting the player and television to display the signal unaltered restores them.