<unk>  exist in two forms; open<unk>  are 'open to all' and cannot be turned off by the viewer; closed<unk>  are designed for a certain group of viewers, and can usually be turned on/off or selected by the viewer – examples being teletext pages, U.S. Closed captions (608/708), DVB Bitmap<unk> , DVD/Blu-ray<unk> . While distributing content,<unk>  can appear in one of 3 types: * Hard (also known as hardsubs or open<unk> . The<unk> text is irreversibly merged in original video frames, and so no special equipment or software is required for playback. Hence, complex transition effects and animation can be implemented, such as karaoke song lyrics using various colors, fonts, sizes, animation (like a bouncing ball) etc. to follow the lyrics. However, these<unk>  cannot be turned off unless the original video is also included in the distribution as they are now part of the original frame, and thus it is impossible to have several variants of subtitling, such as in multiple languages. * Prerendered (also known as closed)<unk>  are separate video frames that are overlaid on the original video stream while playing. Prerendered<unk>  are used on DVD and Blu-ray (though they are contained in the same file as the video stream). It is possible to turn them off or have multiple language<unk>  and switch among them, but the player has to support such<unk>  to display them. Also,<unk>  are usually encoded as images with minimal bitrate and number of colors; they usually lack anti-aliased font rasterization. Also, changing such<unk>  is hard, but special OCR software, such as SubRip exists to convert such<unk>  to "soft" ones. * Soft (also known as softsubs or closed<unk>  are, like closed captions, separate instructions, usually a specially marked up text with time stamps to be optionally displayed during playback. It requires player support and, moreover, there are multiple incompatible (but usually reciprocally convertible)<unk> file formats, but enables greater versatility in post production. Softsubs are relatively easy to create and change, and thus are frequently used for fansubs. Text rendering quality can vary depending on the player, but is generally higher than prerendered<unk> . Also, some formats introduce text encoding troubles for the end-user, especially if different languages are used simultaneously (for example, Latin and Asian scripts). A<unk> track with time stamp also allows for accurate time keeping after having paused the video recording, which would otherwise cause discrepancy between the duration of the video recording since the usually memorized clock time at start and real clock time. Camcorders may record additional metadata such as technical parameters (aperture, exposure value, exposure duration, photosensitivity, etc.). In other categorization, digital video<unk>  are sometimes called internal, if they are embedded in a single video file container along with video and audio streams, and external if they are distributed as separate file (that is less convenient, but it is easier to edit/change such file). +Comparison table Feature Hard Prerendered Soft Can be turned off/on Multiple<unk> variants (for example, languages) Editable Player requirements Visual appearance, colors, font quality Transitions, karaoke and other special effects Distribution Inside original video Separate low-bitrate video stream, commonly multiplexed Relatively small<unk> file or instructions stream, multiplexed or separate Additional overhead
Subtitles
Neuromere
Biomesh
Luts
Voxelotor
Neuromatrix
Globe 
Wart