The reading speed of the “average” viewers (aged between 14-65, from an upper-middle socio-educational class) for a text of average complexity (a combination of formal and informal language) has been proven to range between 150-180 words per minute, i.e. between 2 1/2-3 words per second. This means that a full two line subtitle containing 14-16 words should remain on the screen for a maximum time of something less than 5 1/2 seconds. However, we would actually have to expand the estimate to around 6 seconds because one should also add about 1/4-1/2 of a second that the brain needs to start processing the subtitle it has traced. It should be noted that equal to the importance of retaining a full two-line subtitle for at least 6 seconds to secure ample reading time, is the importance of keeping the same subtitle not more than 6 seconds because this would cause automatic re-reading of the subtitle, especially by fast readers.

根据一项面向14~65岁、中上教育水平观众的研究结果，对书面语、口语的混合阅读速度“平均”为每分钟150~180个词（译者注：word，英文中“单词”的意思，不一定完全对应中文的一个词），即每秒2.5~3个词。

意味着，对于一个由14~16个词组成的双行字幕，出现在屏幕上的持续时间不能低于5.5秒。不过，通常我们都会延长到6秒，因为大脑还需要额外的0.25~0.5秒时间来启动。

需要注意的是，双行字幕保持6秒时间以便确保阅读是十分重要的，同样重要的一点是一句行字幕的停留也不要超过6秒，过长的持续时间会引导观众重读这句话，尤其是对阅读速度快的观众来说。

Note: The average reading speed of children (aged 6-14) has been found to be around 90-120 words per minute. For the subtitling of children’s programmes, then, calculations regarding the duration of the subtitles on screen should be estimated accordingly.

注意：年龄在6~14岁的少儿观众，其平均阅读速度约为每分钟90~120个词。因此儿童节目的字幕时长需要据此进行调整。

Duration of a full single-line subtitle (maximum duration)
单行字幕的（最大）持续时长

Although pure mathematics would lead us to the conclusion that for a full single-line subtitle of 7-8 words the necessary maximum duration time would be around 3 seconds, it is actually 3 1/2 seconds. This happens because for the two-line subtitle it is the visual bulk of the text that signals an acceleration of the reading speed. With the single-line subtitle this mechanism is not triggered. Once again, equal to the importance of keeping a full single-line subtitle for at least 3 1/2 seconds to secure ample reading time, is the importance of retaining the same subtitle for not more than 3 1/2 seconds because this would cause automatic re-reading of the subtitle, especially by fast readers. For similar reasons of automatic re-reading, in both cases of single-line and two-line subtitles, the duration time could be calculated and shortened down to the maximum of the reading time (3 subtitled words per second or 1/3 of a second per subtitled word), if the text is lexically and syntactically easy to process and if the fast pace of the film action dictates such a reduction in the duration of the subtitles.

Duration of a single-word subtitle (minimum duration): The minimum duration of a single-word subtitle is at least 1 1/2 seconds, however simple the word is. Less time would render the subtitle as a mere flash on the screen, irritating the viewers’ eye. Again, it should be noted that equal to the importance of retaining a single-word subtitle for at least 1 1/2 seconds to secure ample reading time is the importance of keeping the same subtitle for not more than 1 1/2 seconds because this would cause automatic re-reading of the subtitle, especially by fast readers.

纯靠计算就能知道，一行由7~8个单词组成的单行字幕持续时间应为3秒左右，但实际上需要3.5秒才够。

这是因为双行字幕有一个天然的视觉引导效应，能够加速阅读，但单行字幕就无法触发这种效应。再一次，单行字幕不低于3.5秒持续时长可确保阅读，同样重要的是不高于3.5秒以避免重复阅读。

无论对于单行还是双行字幕，假如词义较为简单，或者为了匹配快节奏的影片内容，这些情况下都可以减少字幕的持续时长，最快可接受每秒3个词或者一个词1/3秒。

Leading-in time 前导时间

Subtitles should not be inserted simultaneously with the initiation of the utterance but 1/4 of a second later, since tests have indicated that the brain needs 1/4 of a second to process the advent of spoken linguistic material and guide the eye towards the bottom of the screen anticipating the subtitle. A simultaneously presented subtitle is premature, surprises the eye with its flash and confuses the brain for about 1/2 a second, while its attention oscillates between the inserted subtitled text and the spoken linguistic material, not realising where it should focus.

字幕不应该与对应的对白同步出现，而是应该延后1/4秒或更多才出现。有研究表明，大脑需要1/4秒时间来处理它听到的对白然后引导眼睛去寻找屏幕下方的字幕。字幕如果与对白同步出现，观众会觉得晃眼，然后大脑会被迷惑，在1/2秒时间内对于所听和所看的内容产生混乱，分散了注意力。

Lagging-out time 后延时间

Subtitles should not be left on the image for more than two seconds after the end of the utterance, even if no other utterance is initiated in these two seconds. This is because subtitles are supposed to transfer the spoken text as faithfully as possible, in terms of both content and time of presentation and a longer lagging-out time would generate feelings of distrust toward the (quality of the) subtitles, since the viewers would start reflecting that what they have read might not have actually corresponded to what had been said, at the time it had been said.

对白结束后，字幕还停留在屏幕上的时间称为后延时间。后延时间不能超过2秒，即便在那之后没有新的对话也不行。

这是因为字幕要尽可能忠实地还原对白，包括内容和时机两个方面。过长的后延时间会引起对字幕的不信任感，因为观众可能会感觉他们读到的和刚刚听到的内容不匹配。

Between two consecutive subtitles 两屏连续的字幕

About 1/4 of a second needs to be inserted between two consecutive subtitles in order to avoid the effect of subtitles’ “overlay.” This time break is necessary to signal to the brain the disappearance of one subtitle as a piece of linguistic information, and the appearance of another. If no such gap is maintained, the viewers’ eye cannot perceive the change of the new subtitled text, especially if it is of the same length as the antecedent one.

两屏连续的字幕之间应当留有1/4秒间隔，以避免出现字幕的叠加效应（effect of overlay）。这种时间上的间隔能够给大脑一个“这句结束，下句开始”的信号。假如没有了这种间隔，观众的眼睛很可能跟不上新一句字幕，尤其是前后两段字幕的长度差不多时。

“Overlay,” “add-ons” and “cumulative text”
“叠加”、“追加”和“累加”字幕

All these terms are synonymous for the technique of presenting a “dynamic text,” i.e. a dialogue or a briefly paused monologue, with its first part appearing first on the top line of the subtitle and the second part appearing consecutively on the bottom line of the subtitle while the first line still remains on screen. This technique is ideal for avoiding “spilling the beans,” managing to reveal “surprise” information at the time of the actual utterance. Since it is a wild-card mechanism, it should be used cautiously.

这三个是同义词，都是形容同一种字幕形态。假如说话者有停顿，此时字幕应先出前半部分，接着在同屏第二行出后半部分，此时第一行字幕仍然保留在屏幕上。这种方式能够有效避免揭开迷底前就露馅，把悬念保留到了最后一刻。这种方式必须要小心利用。

Camera takes/cuts 镜头切换

Subtitles should respect camera takes/cuts that signify a thematic change in the film product and, for this reason, they should disappear before the cuts. Different camera shots, fades and pans that do not indicate a major thematic change (e.g. a change from a long shot to a close-up and back) should not affect the duration of the subtitles at all as they do not signify a thematic change.

字幕应当遵从镜头以及场景的切换。为此，字幕应当在镜头切换之前就切掉。不涉及到场景切换的叠化或摇移的切镜头（比如从全景切到近景然后再切回）对字幕不构成影响。