Free online STL to PAC converter

Broadcasters, localization vendors, and subtitling systems may require Cavena PAC rather than EBU STL for ingest, playout, delivery, or archive exchange. Converting the file transfers subtitle cues and timing into the binary format expected by the receiving system.

What the STL format is

In video subtitling, STL normally means EBU STL, the binary subtitle format specified by the European Broadcasting Union, not a 3D model. It stores timed subtitle events, cue numbers, timecodes, text, language and character-set information, positioning, justification, and selected presentation flags.

EBU STL files are produced by broadcast subtitle systems and professional editors such as Subtitle Edit, EZTitles, and FAB Subtitler. They commonly arrive from broadcasters, post-production facilities, localization vendors, and archives. The .stl extension alone does not prove that a file is EBU STL, because STL is also used by unrelated formats; confirm the source specification before converting.

What the PAC format is

PAC in this category generally means Cavena PAC, a proprietary binary subtitle format used in professional broadcast and localization workflows. It carries timed events together with production metadata and layout information required by compatible Cavena or broadcast systems.

PAC is useful when a receiving system specifically requests it, but support is not universal. Compatibility can depend on the PAC variant, character encoding, timecode standard, frame rate, language settings, and export profile supported by the target installation.

How to convert STL to PAC

101convert.com provides an online converter for this format, so no software installation is required. Use it as follows:

1. Back up the original .stl file and confirm that it is EBU STL.
2. Open the STL-to-PAC converter on 101convert.com and upload the source file.
3. Choose PAC or Cavena PAC as the output format, if the converter presents both names.
4. Start the conversion and download the resulting file with a .pac extension.
5. Open the output in the destination subtitle or broadcast system and run its validation or import check before delivery.

For offline production workflows, use a professional subtitling application that explicitly lists both EBU STL import and Cavena PAC export, such as an appropriately licensed EZTitles installation. Subtitle Edit or another desktop editor can also be used only when the installed version visibly offers PAC export; format support changes between versions, so do not assume that an STL import option includes PAC output.

When exporting from desktop software, select the recipient's requested PAC profile, character set, language code, frame rate, timecode mode, and field or drop-frame setting. Do not rename .stl to .pac; the two files have different binary structures.

Quality and compatibility limits

The conversion changes the subtitle container and metadata; it does not improve cue timing, spelling, translation, or recognition accuracy. Check the converted file for missing or altered accented characters, apostrophes, italics, underlining, colors, positioning, blank cues, line breaks, and control codes.

EBU STL and PAC can represent layout, safe-area coordinates, justification, colors, character sets, and formatting commands differently. Unsupported attributes may be discarded, remapped, or reduced to plain text. A file that opens successfully can still fail the recipient's downstream validation if it uses an unsupported PAC profile or code page.

Keep the source and destination frame rate and timecode base consistent. Interpreting a 25 fps file as 23.976, 24, 29.97, or 30 fps can shift cue boundaries or create progressive timing drift. Preserve drop-frame or non-drop-frame mode unless the delivery specification explicitly requires conversion, and verify representative cues at the beginning, middle, and end of the programme.