There are three typical opinions about the definition of subtitle translation. Nedergaard-Larsen regards subtitling as “a special type of language transfer: a written, condensed translation of a predominantly spoken original” (Nedergaard-Larsen 1993: 212). This definition is different from two previous forms of inter lingual communication---- interpretation and translation. It is a third form.
Diaz-Cintas has a different idea. He defines subtitling as a linguistic practice which consists in offering, generally in the lower portion of the screen, a written text which sets out to recount the actor’s dialogues and the discursive elements that form part of the image (letters,graffiti, captions, hoarding, etc.) or the sound track (songs, off-screen voices, etc.)”(Diaz-Cintas 2004: 21). He points out the position of subtitle----the lower portion of the screen. Besides, he thinks that subtitle is a translating version of not only dialogues but also some non-oral texts. Just as O’Connell puts forward, the role of subtitling is “supplementing the original voice soundtrack by adding written texts on screen” (O’Connell 2000: 169).
As for Gottlieb, he defines subtitling as “the only type of diasemiotic translation found in the mass media” and it ‘jaywalks’ from source-language speech to target-language writing” (Gottlieb 2004: 248). He defines subtitling “as ‘diasemiotic translation’ in polysemiotic media (including films, TV, video and DVD) in the form of one or more lines of written text presented on the screen in sync with the original dialogue”(Gottlieb 2004: 220). He thinks subtitling can be intra-lingual or inter-lingual from the perspective of linguistics. Intra-lingual subtitling is a transfer process from oral texts to written texts within the same language. It does not involve cultural communication. Inter-lingual subtitling refers to the transfer in both mode and language. Subtitle translation,in a sense, only involves inter-lingual subtitling process, and has nothing to do with Intra-lingual subtitling.
Nedergaard-Larsen thinks that subtitling is a process which transfers an oral original to a written text, and it keeps the same meaning. As for Diaz-Cintas and O’Connell,the two definitions both reveal that subtitling is a language-transfer practice. Gottlieb puts the stress on the perspective of linguistics. All of the authors systematically make a summary of the definition of subtitle playing the part of demonstration role for the other researchers.

3.2 The features of subtitle translation
   Subtitling of movies and TV series has its own distinctive characteristics. When translating, the translator should also bear in mind these features instead of ignoring them. In the following part, we would like to have a discussion about these features that make subtitle translation special and constrained.

3.2.1The semiotic feature of subtitling
 From the point of semiotic feature, Gottlieb(2001) concludes six most important features of subtitiling: prepared communication; using written language; acting as an additive; synchronous semiotic channel; as part of a transient; polysemiotic text.
The traits mentioned above give an accurate and distinctive description of subtitling. Subtitling is prepared communication. Different from an interpreter, a subtitle translator does not need to do simultaneous translation. To some extent, the audiovisual texts are ready and the translator can translate freely without time restriction. Even though in some cases the translator is given a certain amount of time, it is still different from simultaneous or consecutive interpreting. As for “using written language”, it undoubtedly reveals that subtitling is not interpreting. The product of subtitling should be a written form instead of an oral form. The transformation from oral texts to written texts can be regarded as a “semiotic switch from the spoken to the written word” (Pedersen 2007: 19). Moreover, in some cases, written forms are more formal. Subtitling can act as an additive, and it means that some information can be added to the screen through subtitling. For instance, the complementary information is an explanation of the scene which involves too many complicated messages that are too difficult for ordinary audience to understand. Through subtitling, it is more easily for viewers to obtain a correct understanding. The additive feature of subtitling provides constant access to the source text for the audience. 《疯狂动物城》从接受理论角度研究动画电影字幕翻译(4):http://www.751com.cn/yingyu/lunwen_18840.html