![1girl :o animated bad_id bad_link bad_twitter_id bangs bed_sheet black_hair black_legwear blue_swimsuit blush bow braid breasts cherry_blossoms closed_eyes clothes_removed dutch_angle floral_print from_above hair_bow hands_up hangaku implied_sex isonami_(kantai_collection) kantai_collection kneehighs legs_up long_hair lying mp4 name_tag on_back on_bed one-piece_swimsuit open_mouth raised_eyebrows red_bow school_swimsuit small_breasts spread_legs swimsuit twin_braids wince rating:q score:13 post #2551274](/cdn_image/preview/b9/2b/b92b5cce868e417dab840a625bcb68f4.jpg)
MPEG-4 Part 14 or MP4 is a multi-purpose container format based on Apple's QuickTime format. It is an ISO standard (ISO/IEC 14496-14). It can be used for audio as well as video. It is mostly used to contain H.264 (MPEG-4 Part 10) compressed video with/and/or AAC (Advanced Audio Coding) or MP3 compressed audio. Modern browsers can directly stream MP4 files.
H.264 is the most used video format for video streaming while AAC is the successor to MP3, being more efficient than its predecessor. MP3 is still by far the most used audio format.
This tag implicates animated (learn more).