Translating captions

You can use the cctranslate tool (implemented by Oleg) to translate extracted captions in realtime and in SubRip formatted files. We use the Google Translate API for translation, but the tool is built so developers can easily add other translation engines.

How realtime translation works?

ccextractor starts with sharing service on
ccextractor launches cctranslate process
launched instance of cctranslate subscribes to ccextractors' messages
ccextractor publishes extracted subtitles to all subscribers
cctranslate requests translation from translation service and saves translated captions to an output file

Sharing service is a Publisher-Subscriber IPC Pattern publisher implementation. It uses nanomsg as a cross-platform socket library, that provides simple interface to implement pub-sub model and supports lots of transport mechanisms. To serialize messages protobuf-c implementation of Google Protocol Buffers is used. Both of used solutions are language-independent, so sharing service could be easily used by third-party developers to create new solutions based on ccextractor.

What about the cctranslate tool?

Cctranslate tool was designed to be cross-platform and is implemented in C language. It uses:

libcurl to perform http/https requests
nanomsg as a socket library
protobuf-c to parse serialized messages
CJSON to parse responses from Google Translate API

Standalone SubRip-formatted files could also be translated using this tool along with realtime translation.

Coming soon in a separate document

How to use it?

First, you have to compile it. It uses cmake build automation system, so make sure you have it installed. For Linux/MacOSX/UNIX use:

$ mkdir build && cd build
$ cmake ../
$ make

Make sure nanomsg and libcurl dev packages are downloaded. If your distribution doesn't have a package system or these packages are not supported by maintainer, you can download tarballs and compile it by yourself.

Then, create a Google CloudPlatform account (or use your existing) and generate an API key.

Using cctranslate as a standalone text file captions translator

Check what languages are available at the moment:

$./cctranslate --list-langs --key=YOUR_API_KEY

Pick up languages you want your subs be translated to, and run:

$./cctranslate --input=subs.srt --langs=fr,it,th --key=YOUR_API_KEY

Using cctranslate for realtime translation

Copy cctranslate tool to ccextractors' binary directory. There are two ways to translate realtime: launch ccextractor with translating mode on and launch cctranslate tool to connect to already running instance of ccextractor.

To launch ccextractor with translating mode on, run:

$ ./ccextractor INPUT_OPTIONS -translate LANGUAGE_LIST -translate-auth YOUR_API_KEY

To connect cctranslate tool to already running instance of ccextractor:

$ ./cctranslate --source=extractor --key=YOUR_API_KEY

In the second case, ccextractor has to be started with sharing service on. To do that add -enable-sharing option to arguments. By default, it starts TCP sharing service on localhost:3269. You can set other nanomsg-supported transport type to share captions using -sharing-url arg in format transport:address.