Mp4 Multimedia Player Manual
In digital encoding, there are two main ways of including subtitles in a video. There is softsubbing, and hardsubbing. Both methods has unique advantages and disadvantages, along with various arguments both for and against each method.
Hardsubbing is a method that "burns in" subtitles into the actual video portion of a movie. Digital hardsubs are much like subtitled VHS tapes; the subtitles cannot be turned off.
Advantages of Hardsubbing
Hardsubbing is usually much less demanding on the playback device. Since the text is already part of the video, it will only take as much processing as the unsubtitled video would. You are also often able to make special effects that would be difficult to replicate in a soft subtitle format, because of the large amount of CPU usage required to renderer them. Even in softsubbed anime fansubs, the opening and closing karaoke are often hardsubbed because of the special effects used.
Some people argue that with hardsubs, scripts are harder to steal, since the text is embedded in the image - thieves cannot simply extract subtitles as in a softsub. However, the presence of very good subtitle extractors designed for the purpose of extracting this embedded text removes much of the argument that hardsubs prevent script stealing.
Many playback devices and computer platforms cannot display the special fonts and formattings that softsubs contain, but this problem is removed with hardsubs, where the style is preserved. Also, these stylings will show back exactly the same on any device, unlike softsubs which depend on the playback device to properly intrepret and display the stylings.
Disadvantages of Hardsubbing
Despite what some may call numerous advantages for hardsubbing, there are several distinct disadvantages that should be evaluated before making a decision.
The method of hardsubbing requires that the source video is re-encoded so the subtitles can be written on the image. This, by the nature of lossy video encoding, causes a reduction in video quality.
Subtitles add a sharp contrast in a video image due to their nature. This will cause compression artifacts along the edges of the encoded subtitle, and blurring of the subtitle. This effect is especially evident at lower bitrates.
Under typical circumstances, the inclusion of the subtitles will cause an increase in the bitrate needed for the video to keep the same quality. This, of course, means an increased filesize, or lower quality at the same size. The increase in bitrate necessary is typically around 3 to 10%.
Changing the subtitles requires a re-encode of the video source, which can add a lot of time and extra work to the release process.