: In the context of these file names, "ES" often indicates "English Subtitles," suggesting the video has been subtitled for English-speaking audiences.
: This is the "production code" or "ID" used by the Japanese adult video (JAV) studio S1 No. 1 Style .
In the media industry, these alphanumeric codes are the primary way content is cataloged, searched, and identified by consumers and distributors. The "SSIS" prefix is specific to the S1 studio's "S1 Star" series, which features prominent performers from their roster.
: This is a standard digital multimedia container format used for storing video and audio.