Captioning For Digital Cinema Packages

Luke Kreger

Jun 4
4 min read

Theaters are striving to become more accessible to everyone. This means that filmmakers will often be required to provide caption files for their films. Those caption files must meet certain requirements that are determined by SMPTE (the organization that creates all the standards for cinema).

Create a source caption file

The first step in creating caption files is to generate a source caption file in .srt format. You can do this by exporting your caption track in editing software, like Premiere Pro, or use an online service to automatically generate your caption text. Our favorite service for generating caption text is

When creating the caption file, it’s crucial to keep in mind the SMPTE subtitle/caption standards. Failure to do so puts your DCP at risk of being rejected by the cinema server. The most common issues with DCP caption tracks are:

1. Too many characters per line (maximum of 32 characters including spaces)

2. Too many lines per captions (maximum of 2 lines per caption)

After generating the .srt file, it’s essential to view it in a text editor to ensure it adheres to the SMPTE requirements before proceeding to create a timed text file for DCP. Double check that your caption track falls within the character and line limits.

Convert to the correct frame rate

If your film has a frame rate of 23.97 or 29.97, then you will need to do a frame rate conversion. DCP does not accept fractional frame rates, so you’ll need to convert them to a DCP compliant frame rate like 24 or 30 fps. Tools like MacCaptions or Subtitle Edit can help with the frame rate conversion. If this conversion is not done, it can lead to the captions drifting out of sync during playback.

Stay under the size limit

Once you have your source file and have done the necessary frame rate conversion, you will need to make a timed text file that is less than 256KB. There are two main strategies for keeping your file size low:

1. Sourcing a simple font file (one with only essential characters that is legible)

2. Breaking the captions into reels

The font file is a necessary part for the creation of your DCP compliant timed text file. This font file will be used by the DCP to reference what font to display your captions with. If your DCP is a feature film, you will likely need to break it up into reels to adhere to the SMPTE size limits. Reels are created by breaking up your film into sections during the DCP creation process. A typical feature with captions will likely have 3–6 reels depending on the length of the film.

Choose how your captions appear on screen

Before making your Digital Cinema Package (DCP), you will also need to decide how you want your captions to be displayed. Typically, closed captions use a periphery device to display the captions to each individual audience member, while open captions are burned into the film. These both have their own trade offs. Burning in the captions allows you more flexibility with the font you want used for the captions and avoids having to adhere to SMPTE guidelines. The down side of OCAPs is that the captions are obscuring the view of the picture. Closed captions allow for display flexibility, but you will need to go through the process of creating SMPTE compliant timed text files.

Consider versioning your DCP

You will also need to consider whether to include the captions in your original version (OV) or add them as a version files (VF) to an already existing DCP. These have their own trade offs as well. A VF with captions must be paired with the OV for playback because a VF is just a supplemental package and needs the OV to reference the picture and sound. A DCP with captions in the OV will not need any supplemental files to display the captions properly. If you plan to distribute your DCP to other countries, you may want to use version files to output multiple languages. Version files are a great way to add captions and subtitles to an already existing DCP without having to rewrap the DCP.

Be aware of software limitations

Finally, it’s essential to consider software limitations when creating SMPTE timed text files. Some software may have limitations when creating DCPs with captions. For example, Resolve does not have the capabilities to create DCPs with closed captions. In such cases, it may be necessary to use a different software or service to create the files.

Accessibility is the future

Accessibility requirements are on the rise in the film industry. Many festivals and venues require that filmmakers adhere to these new accessibility standards. Although the captioning process is time intensive, accessible films are more universally accepted and inclusive. If you’re feeling overwhelmed, Cinematiq can help create cinema compliant timed text files for your DCP. Reach out today and make your film more accessible for your audience.

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