Convert SRT to PAC

Broadcasters, playout servers, and caption-delivery vendors may require a Screen Subtitling Systems PAC file instead of the .srt file produced by a transcription service or video editor. The export must match the recipient’s requested frame rate, PAC variant, character encoding, and layout rules.

What SRT files contain

SRT is a plain-text subtitle format used by video platforms, transcription services, DVD tools, and subtitle editors. Each cue contains a sequence number, start and end times in milliseconds, and subtitle text, for example 00:01:12,400 --> 00:01:15,000.

SRT is easy to edit in a text editor, but it does not reliably carry broadcast presentation data such as a required font, safe-area position, colour palette, or delivery profile. HTML-like tags, unsupported symbols, and custom speaker formatting may not survive PAC export.

What PAC files contain

In subtitle workflows, .pac normally means the binary Screen Subtitling Systems PAC format used by broadcast subtitling and playout systems. It can store timed captions and supported display attributes, including positioning and colour information, for compatible systems.

PAC is unrelated to a web proxy auto-configuration .pac file, which contains JavaScript. A subtitle PAC file must be opened or validated with subtitle software or the recipient’s broadcast system.

PAC delivery rules vary by customer and system. Legacy PAC variants commonly use restricted character sets and may impose limits on subtitle rows, characters per line, colours, positions, and reading speed. Unicode-capable PAC variants exist, but older playout equipment may reject them.

Convert with Subtitle Edit

Subtitle Edit is a practical free desktop option for checking and exporting many subtitle formats, including Screen PAC where supported by the installed version. For deliveries requiring a customer-specific template, automated compliance checks, or certified broadcast workflows, use professional tools such as EZTitles or WinCAPS.

1. Keep the original file unchanged, for example programme.srt.
2. Open the SRT file in Subtitle Edit using File → Open.
3. Load the reference master through Video → Open video file, then check that cue in and out times match the picture.
4. Confirm the master frame rate and the recipient’s required delivery rate. Common rates include 23.976, 24, 25, 29.97, and 30 fps. Do not change subtitle frame rate unless the programme master has also been frame-rate converted.
5. Check overlaps, reading speed, line breaks, maximum lines, and characters per line. Manually split or rephrase long subtitles instead of relying on automatic wrapping.
6. Select File → Save as, choose the requested PAC (Screen) format or PAC variant, and save as programme.pac. Set the language, code page or Unicode option, colours, positioning, and other export settings only as specified by the recipient.
7. Reopen the PAC file in Subtitle Edit or test it in the target playout system. Compare cue timing, accented characters, line breaks, and positioned captions against the reference video.

Online and professional conversion options

Do not use a general-purpose file converter unless it explicitly supports the required Screen PAC variant and lets you select the required frame rate and encoding. Hosted subtitling systems such as OOONA or CaptionHub may provide PAC export within configured broadcast workflows, but PAC availability and output profiles depend on the account and recipient setup.

For confidential or unreleased programmes, desktop or approved enterprise subtitling systems avoid uploading dialogue and timing data to an unknown conversion service. Send a test PAC file before converting an entire series or delivery batch.

Compatibility checks

Ask for a PAC sample file or written delivery specification before export. It should state the required PAC flavour, frame rate, language or code page, maximum rows and line length, safe area, font and colour requirements, and any required subtitle start time.

SRT timestamps use milliseconds, while PAC timing is represented according to the target video timing system. Exporting rounds cue boundaries to available frame positions, so a shift of up to one frame can occur. Larger timing errors usually indicate an incorrect frame rate or confusion between rates such as 25 fps and 29.97 fps.

Legacy 8-bit PAC output can corrupt characters outside its selected code page, including Cyrillic, Arabic, CJK text, emoji, and some accented characters. Use a Unicode PAC variant only when the receiving system explicitly accepts it, and test representative multilingual subtitles before delivery.