What Are PGS Subtitles? PGS Format, SUP Files, and SRT Conversion

PGS subtitles are image-based subtitles commonly associated with Blu-ray video. PGS stands for Presentation Graphic Stream. Instead of storing each subtitle as normal editable text, PGS stores the subtitle as graphical data that is displayed on screen.

This difference matters when you want to edit or convert the subtitles. A text subtitle can already contain the words as characters. A PGS subtitle needs the words to be recognized from the subtitle images before they can become editable text.

What Does PGS Stand For?

PGS stands for Presentation Graphic Stream. Software may also identify the format as HDMV PGS, HDMV Presentation Graphic Stream, or hdmv_pgs_subtitle.

These names refer to the same image-based subtitle type in this context. For example, FFmpeg identifies PGS as AV_CODEC_ID_HDMV_PGS_SUBTITLE and describes it as HDMV Presentation Graphic Stream subtitles.

Is PGS a Text or Image Subtitle Format?

PGS is a bitmap subtitle format. This means the subtitle content is stored as graphical subtitle images rather than plain text characters.

A PGS subtitle stream contains more than just the visible subtitle picture. It also includes information used to control how the subtitle is presented. Software decoders use data for subtitle objects, palettes, positions, and display timing to build the subtitle shown on screen.

The main difference from SRT is easier to understand in a table:

What Is a SUP Subtitle File?

SUP is commonly used as the file extension for raw PGS subtitle data. A file may therefore appear as:

movie.sup

The .sup file can contain HDMV Presentation Graphic Stream subtitle data. FFmpeg, for example, uses sup as the format name for raw HDMV Presentation Graphic Stream subtitles and lists .sup as its extension.

This is why PGS subtitles and SUP subtitles are often discussed together. PGS describes the subtitle format, while SUP is commonly the file you work with after that PGS subtitle stream has been stored or extracted.

What Does hdmv_pgs_subtitle Mean?

You may see hdmv_pgs_subtitle when inspecting a video or subtitle stream with media software.

It is a technical identifier used for HDMV Presentation Graphic Stream subtitles. Seeing it usually tells you that the subtitle stream is PGS and image-based rather than a normal text subtitle such as SRT.

Like other PGS subtitle streams, subtitle data labeled hdmv_pgs_subtitle can be converted to SRT using OCR, the same way described below.

How PGS Subtitles Work

A PGS decoder reads several types of data to build the subtitle image. These can include subtitle objects, color palette information, presentation information, and display instructions.

The subtitle image itself can use run-length encoded image data. The decoder then uses the available presentation information to place and display that subtitle correctly.

For most users, the important point is simpler: the subtitle words are part of an image. They are not already stored as editable text.

Why PGS to SRT Conversion Needs OCR

SRT is a text-based subtitle format. PGS is image-based. Because the two formats store subtitles differently, converting PGS to SRT requires recognizing the words shown inside the PGS subtitle images.

This process is called optical character recognition, or OCR. OCR reads the characters from each subtitle image and turns them into text. The resulting text and subtitle timing can then be written into an SRT file.

A normal format change alone cannot turn the graphical letters into editable subtitle text. The text first needs to be recognized.

How to Convert PGS Subtitles to SRT

If your goal is conversion rather than learning about the format, use the site’s PGS to SRT converter.

The basic process is:

1. Provide the PGS or SUP subtitle file to the converter.
2. The subtitle images are processed with OCR.
3. The recognized subtitle text is combined with its timing.
4. The result is saved as an SRT subtitle file.

Can You Convert a SUP File to SRT?

Yes, when the SUP file contains PGS subtitle data, the same image-to-text problem applies. The subtitle images need OCR before the recognized words can be written as SRT text.

For a SUP file, use the site’s SUP to SRT converter.

Can FFmpeg Convert PGS Directly to SRT?

FFmpeg recognizes PGS as an image-based subtitle codec and SRT as a text-based subtitle codec. FFmpeg’s documentation also distinguishes between image-based and text-based subtitle streams when handling subtitle output.

As explained above, this means an OCR step is still needed to produce SRT text. FFmpeg alone does not read the words out of the subtitle images.

For the site’s detailed FFmpeg workflow, read the PGS to SRT with FFmpeg guide.

PGS Subtitle FAQ