Translating SRT Subtitles with the Three-Step Reflection Method

Andrew Ng's "Reflective Three-Step Translation Method" is highly effective. It enhances translation quality by allowing the model to self-review the translation results and suggest improvements. However, directly applying this method to SRT format subtitle translation presents some challenges.

Specific Requirements of SRT Subtitle Format

SRT format subtitles have strict formatting requirements:

• First line: Line number (numeric)
• Second line: Two timestamps connected by -->, in the format hours:minutes:seconds,milliseconds
• Third line and onwards: Subtitle text content

Subtitles are separated by two blank lines.

Example:

1
00:00:01,950 --> 00:00:04,430
Several molecules have been discovered in the five-star system,

2
00:00:04,720 --> 00:00:06,780
We are still multiple universes away from third-type contact.

3
00:00:07,260 --> 00:00:09,880
Weibo has been carrying out filming missions for years now,

4
00:00:10,140 --> 00:00:12,920
Many previously difficult-to-capture photos have been transmitted recently.

Common Problems in SRT Translation

When using AI to translate SRT subtitles, the following problems may occur:

• Format Errors:
  • Missing line numbers or duplicated timestamps
  • Translating English symbols in timestamps into Chinese symbols
  • Merging adjacent two subtitle text lines into one line, especially when the previous and next sentences form a complete sentence grammatically.
• Translation Quality Issues:
  • Even with strict prompt word limitations, translation errors often occur.

Common Error Examples:

• Subtitle text merging leading to blank lines

• Format disorder

• Line number being translated

• Inconsistent number of original and translated subtitles

As mentioned above, when the previous and subsequent subtitles belong to the same sentence grammatically, they are likely to be translated into the same one, resulting in a missing number of subtitle entries.

Formatting errors directly prevent subsequent processes that depend on SRT from working. Different models exhibit different errors and probabilities. Relatively speaking, more intelligent models are more likely to return legal and compliant content, while locally deployed small-scale models are almost completely unusable.

However, given the improvement in translation quality provided by the three-step reflection method, I still tried it. I eventually chose to use gemini-1.5-flash for a small experiment, mainly because it is intelligent enough and free. Besides frequency limitations, it has almost no other restrictions.

Prompt Writing Strategy

Following Andrew Ng's three-step reflection workflow, I wrote the prompts:

• The first step requires the AI to translate literally.
• The second step requires the AI to evaluate the literal translation and provide optimization suggestions.
• The third step re-translates idiomatically based on the optimization suggestions.

The difference is that I strengthened the requirement that the returned content must be in a legal SRT format, although it may not always comply 100%.

Building a Simple API

One problem with the three-step reflection mode is that it consumes significantly more tokens. The prompts become longer, and the output results become longer. In addition, due to Gemini's frequency limit, exceeding the limit will return a 429 error. You need to pause for a while after each request.

Using Flask to build a back-end API, and Bootstrap 5 for a simple front-end single page. The overall interface is as follows:

Obviously, a VPN is necessary to use Gemini in China.

• Simultaneous translation lines: refers to the number of subtitle lines in a single translation request. If it is too large, it may exceed the token limit and cause errors. If it is too small, it is meaningless. It is recommended to be within 30-100, with a default of 50.
• Pause seconds after translation: To prevent requests from being too frequent and causing a 429 error, the process will pause for 10 seconds after each request before initiating the next request.

Example of returned results:

<step1_initial_translation>
1
00:00:01,950 --> 00:00:04,430
Several molecules have been discovered in the five-star system,

2
00:00:04,720 --> 00:00:06,780
We are still multiple universes away from third-type contact.

3
00:00:07,260 --> 00:00:09,880
Weibo has been carrying out filming missions for years now,

4
00:00:10,140 --> 00:00:12,920
Many previously difficult-to-capture photos have been transmitted recently.

5
00:00:13,440 --> 00:00:17,500
In early June, astronomers published this photo in Nature,

6
00:00:18,040 --> 00:00:19,180
Outside the blue core,

7
00:00:19,360 --> 00:00:21,380
There\'s also this circle of orange light,

8
00:00:21,900 --> 00:00:23,740
This is a new drama-scale sweet donut,

9
00:00:24,380 --> 00:00:25,640
This is a portal.

10
00:00:26,280 --> 00:00:28,100
This is the generation ring of an alien civilization,

</step1_initial_translation>

<step2_reflection>
* **Line 1:** "Five-star system" is likely a mistranslation.  It probably refers to a five-member committee or group, not a star system. Clarify the context.
* **Line 2:** "Multiple universes" seems like an over-exaggeration.  Rephrase for clarity and accuracy.
* **Line 3:** "Weibo" should be explained as a Chinese social media platform.  "Filming missions" is unclear.  Does it mean "posting videos/images"?
* **Line 8:** "Drama-scale sweet donut" is a nonsensical literal translation. Figure out the intended meaning.
* **Line 9:** "Portal" seems out of context.  Verify the intended meaning.
* **Line 10:** "Generation ring" is likely a mistranslation.  Clarify the context.
* **Line 11:** "Organic polycyclic aromatic hydrocarbons" is overly technical for a general audience. Simplify if possible.
* **Line 12 and 14:** Use the correct formatting for the galaxy\'s name: SPT0418-47.
* **Line 15:** "It hasn\'t been shortened" is awkward. Remove or rephrase.
* **Line 28:**  The name of the organization and the resource should be translated more naturally and accurately.  Consider breaking this long line into two for better readability.
* **Line 29:**  "Cute plush dolls" may sound childish. Consider rephrasing as "animated characters" or similar.
* **Line 35:** "James Webb Space Telescope" should be used consistently throughout. Shortening to "Webb Telescope" after the first mention is acceptable.
* **Line 44:** "SPD048" is likely a typo.  It should be SPT0418-47 to be consistent.
* **Line 45-46:**  "Standard beautiful photo" is redundant.  Simplify to "beautiful photo".
* **Line 48:** "Grovitational Lenshin" is a typo. Correct to "Gravitational Lensing".
* **Line 50:** The sentence is incomplete. Finish the thought.

</step2_reflection>

<step3_refined_translation>
1
00:00:01,950 --> 00:00:04,430
Several molecules have been discovered in the five-member group\'s area of focus.

2
00:00:04,720 --> 00:00:06,780
We are still far from making contact with extraterrestrial life.

3
00:00:07,260 --> 00:00:09,880
The James Webb Space Telescope has been capturing images for a year now,

4
00:00:10,140 --> 00:00:12,920
and has recently transmitted many previously unseen photos.

5
00:00:13,440 --> 00:00:17,500
In early June, astronomers published this image in Nature.

6
00:00:18,040 --> 00:00:19,180
Outside the blue core,

7
00:00:19,360 --> 00:00:21,380
there\'s a ring of orange light.

8
00:00:21,900 --> 00:00:23,740
This is a large, ring-shaped structure.

9
00:00:24,380 --> 00:00:25,640
This is being investigated.

10
00:00:26,280 --> 00:00:28,100
This is thought to be a sign of an early galaxy.

</step3_refined_translation>

Extract the text within the <step3_refined_translation></step3_refined_translation> tags from the results, which is the translation result.

Simple Package Available for Local Trial

Download directly, extract the files, and double-click app.exe to automatically open the UI interface in your browser. Enter the Gemini API key you obtained, fill in the proxy address, select the SRT subtitle file to be translated, and select the target language to translate to, and try the results.

Q1: How does the reflection workflow differ from traditional machine translation?

A1: The reflection workflow introduces a self-assessment and optimization mechanism, simulating the thinking process of human translators, and can produce more accurate and natural translation results.

Q2: How long does it take to use the reflection workflow?

A2: Although the reflection workflow requires multiple AI processing steps, it usually only takes 10–20 seconds longer than traditional methods. Considering the improvement in translation quality, this time investment is worthwhile.

Q3: Can the reflection workflow guarantee that the subtitle translation results are always legal SRT?

A3: No, there may still be problems with blank lines and inconsistencies with the number of original subtitles. For example, if the second of two consecutive subtitles only has 3-5 words and grammatically belongs to the previous sentence, the translation results are likely to be merged into one.

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Added a feature to the tool to support uploading video or audio files simultaneously. With the help of Gemini, audio and video can be converted into subtitles, and at the same time, the subtitles can be translated and the translation results returned.

The Gemini large model itself supports both text and audio-visual formats, so a single request can realize transcription from audio and video to subtitles and translation.

For example, if an English-speaking video is sent to Gemini and specified to be translated into Chinese, the returned result will be Chinese subtitles.

1. Translate Subtitles Only

You can paste SRT format subtitle content into the text box on the left, or directly click the "Upload SRT Subtitles" button to select a subtitle file from your local computer.

Then set the target language you want to translate to, and you can use the "Three-Step Reflection Translation Method" to instruct Gemini to perform the translation task, return the results to the text box on the right, and click the "Download Button" in the lower right corner to save it as an SRT file to your local computer.

2. Transcribe Audio and Video into Subtitles

Click the "Upload Audio/Video to Transcribe to Subtitles" button on the left, select any audio or video file to upload. After the upload is complete, submit it. After processing, Gemini will return the subtitle content recognized from the audio and video, and the effect is good.

If you specify the target language at the same time, Gemini will continue to translate the result into the language you specify after recognition and return it. That is, it completes the two tasks of generating subtitles and translating subtitles at the same time.

Download address:

https://github.com/jianchang512/ai2srt/releases/download/v0.2/windows-ai2srt-0.2.7z