How to Extract PGS Subtitles from MKV with FFmpeg

Before You Start

• MKV or compatible source containing an embedded PGS subtitle track.
• Current FFmpeg build with FFprobe.
• Read access to the source file.
• Write access and sufficient storage for the SUP output.
• Permission to process the media and subtitle track.

If FFmpeg is not installed, download FFmpeg from the official website. The official FFmpeg documentation explains input files, mapping and stream copy behavior.

Identify the PGS Subtitle Track

Inspect the file before extraction. The first subtitle stream may not be PGS, several tracks may share the same language, and a file can contain full, forced, SDH and commentary subtitles. Language metadata can also be missing or inaccurate. A text subtitle track should not be extracted into a .sup filename.

Inspect Streams with FFmpeg

Run FFmpeg without an output file to inspect the input streams:

ffmpeg -i input.mkv

Representative output may look like this:

Stream #0:2(eng): Subtitle: hdmv_pgs_subtitle
Stream #0:3(spa): Subtitle: hdmv_pgs_subtitle

In this example, 0:2 and 0:3 are absolute stream indexes. The eng and spa values are language tags when present. The hdmv_pgs_subtitle codec label identifies PGS subtitle images. These values are examples and must not be copied without inspecting your own file.

Inspect Subtitle Metadata with FFprobe

The official FFprobe documentation covers stream inspection. This cross-platform command lists subtitle indexes, codec names and language/title metadata without requiring grep:

ffprobe -v error -select_streams s -show_entries stream=index,codec_name:stream_tags=language,title -of default=noprint_wrappers=1 input.mkv

index=2
codec_name=hdmv_pgs_subtitle
TAG:language=eng
TAG:title=English PGS

Confirm the PGS Codec Label

hdmv_pgs_subtitle is FFmpeg's codec label for image-based Blu-ray PGS subtitles. It confirms that the selected stream contains PGS subtitle images rather than ordinary text captions. For more background, read how PGS subtitles work.

Extract PGS as SUP with FFmpeg

Use a Relative Subtitle Selector

ffmpeg -i input.mkv -map 0:s:0 -c:s copy output.sup

Use an Absolute Stream Index

If inspection shows this example stream:

Stream #0:3: Subtitle: hdmv_pgs_subtitle

Use this example command after replacing the stream index with the one from your file:

ffmpeg -i input.mkv -map 0:3 -c:s copy English-PGS.sup

The 0:3 value is only an example. The first number identifies the input. The second identifies the absolute stream index. Your actual stream number must come from your inspection output.

Relative and Absolute Selectors Compared

These selector styles are not interchangeable. The FFmpeg stream mapping guide is a useful practical reference after you understand the inspected stream list.

Windows, macOS and Linux Commands

The core FFmpeg syntax is the same across supported operating systems, but file paths and shell quoting differ. Quote paths containing spaces, replace 0:3 with the inspected PGS stream, and treat file paths as examples.

Windows PowerShell

ffmpeg -i "C:\Videos\Movie File.mkv" -map 0:3 -c:s copy "C:\Videos\English-PGS.sup"

If Windows reports ffmpeg is not recognized, FFmpeg is not installed or its executable directory is not available through PATH. Install FFmpeg from a trusted source or use the correct executable path.

macOS and Linux

ffmpeg -i "/path/to/Movie File.mkv" -map 0:3 -c:s copy "/path/to/English-PGS.sup"

File paths can be case-sensitive on macOS and Linux. Do not add distribution-specific package-manager commands unless you are following current instructions from a trusted source.

What the Extracted SUP File Contains

The output SUP file carries the selected PGS subtitle data, including subtitle images and timing information from the stream. It does not contain editable dialogue text. Renaming output.sup to output.srt does not convert the format; OCR is still required.

Stream copy preserves the selected subtitle stream without OCR or subtitle-image re-encoding.

Verify the Extracted SUP File

1. Confirm FFmpeg completed without a fatal error.
2. Confirm the output exists and is not empty.
3. Optionally inspect the opening bytes.
4. Preview or process the track to confirm actual content.

On Linux and macOS, you can inspect the file size with:

ls -lh output.sup

Windows users can inspect file properties. Do not rely on a fixed valid size because a short or forced subtitle track can be small.

On Linux and macOS, this optional sanity check inspects the beginning of the file:

xxd -l 16 output.sup

A typical PGS SUP stream commonly begins with a PG packet signature. This can confirm that the file resembles PGS data, but it cannot prove that the correct language, full/forced track or complete subtitle content was extracted.

Extracting Forced PGS Subtitles

Forced captions often cover foreign-language dialogue, signs or essential translations. They may exist as a separate track, or they may be flagged within a larger track. Several tracks may share the same language, and language metadata alone does not reliably identify a forced track.

1. Inspect language, title, default and forced metadata.
2. Treat metadata as a clue rather than proof.
3. Extract plausible tracks to different filenames.
4. Preview or OCR each track.
5. Keep the track matching the desired content.

Common FFmpeg Errors and Solutions

ffmpeg: command not found or ffmpeg is not recognized

FFmpeg may not be installed, the executable may not be in PATH, or the terminal may need to be reopened after installation. Verify the install or use the full executable path.

Output format not recognized

Possible causes include selecting a non-PGS stream, using an output extension that does not match the selected codec, choosing the wrong stream index, or using an FFmpeg build that cannot determine the output format from the filename.

1. Inspect the streams again.
2. Confirm the selected stream is hdmv_pgs_subtitle.
3. Confirm the stream index.
4. Use stream copy.
5. Add explicit SUP format only when needed.

ffmpeg -i input.mkv -map 0:3 -c:s copy -f sup output.sup

The 0:3 selector is only an example. Explicit -f sup is a fallback when normal format detection from the output name does not work as expected. It does not fix a wrong source stream.

The SUP file is empty

The wrong stream may have been selected, the source may be damaged or unusual, the mapping may be incorrect, the track may have little or no subtitle content, or FFmpeg may have ended with an error. OCR has not started at this stage, so OCR is not the cause of an extraction failure.

The wrong language was extracted

Check the absolute stream index, relative subtitle index, language tag, track title, forced/default metadata and other PGS tracks.

Several tracks use the same language

They may represent full subtitles, forced captions, SDH captions, commentary or alternate translations. Select and test deliberately.

Permission denied or cannot write output

Choose a writable output folder, quote paths containing spaces, confirm the source is readable and make sure another application is not locking the destination file.

The SUP file converts poorly with OCR

Extraction can be correct while OCR still struggles. Recheck the subtitle language, try a more accurate OCR profile and manually review names, accents, punctuation and similar-looking characters.

Why the FFmpeg output is SUP instead of SRT

This is expected. PGS subtitles are images. FFmpeg can extract the image-based stream but cannot recognize the words inside it. OCR is required to create SRT text.

Related SUP and PGS Guides

Browse all subtitle extraction and conversion guides.

Frequently Asked Questions