Generally, it is not necessary to extract subtitles from a DVD. These are freely available on the internet and with the right tools, downloading the correct subtitle is just a click away. But if you have ripped a movie from a DVD the subtitle you download from the internet might not sync correctly with the video. Or if the movie is a rare one and there are no subtitles available yet, it might become necessary to extract the subtitle files from the DVD as well. This guide will teach you how to do that, but first you have to understand how DVD subtitles work.
The subtitles that you use when playing media files on the PC is different from the subtitles that you find on DVDs or Blu-ray discs. Subtitles in DVDs are contained in VOB files, along with the main video and audio streams, as separate video frames that are overlaid on the original video stream while playing. The subtitles you see on a DVD is just a stream of image files which appear one after the other. Unlike the text based subtitle files, subtitles on DVD cannot be edited, scaled or modified in ways that is possible with text based subtitle files.
Extracting subtitles from a DVD is hence a two step process. First the VOB file needs to be demuxed and the subtitle stream extracted, and then the stream needs to be fed into an OCR software to convert the images into text. That’s quite a task. Fortunately, DVDSubEdit is a software that does both seamlessly and transparently to the user.
DVDSubEdit allows you to visualize and make modifications to the subpics (subtitles or button highlights in menus) directly inside the VOB files, without the need to demux and remux the subpic stream. It scans the VOB files for subpicture packs and parses the packs to display the subpicture data. Then it displays the subpicture commands, along with their parameters, allowing you to move the subpicture up and down in the video frame and change the color and transparency of selected pixel types. It's also possible to change normal subtitles into forced subtitles and vice versa.
As you can see from the image above, the program interface is cluttered with controls. However, the only controls that are actually needed for our job are marked in red. All you have to do is load the VOB file containing the movie and click the ‘Run OCR’ button, wait till OCR is completed and then save the results with the ‘Save as SRT’ button.
The rest of the controls usually comes handy if the program fails to correctly recognize the text in the images. In that case you can adjust the subpics color, opacity etc to enhance visibility.
If the movie is split into multiple VOB files, which is common in DVDs, you have to load each VOB file individually. This results in multiple SRT files, one for each VOB file. You can merge the SRT files into one using programs such as Subtitle Workshop, which is the best subtitle editing software available.
The resulting SRT file can be loaded into any media player supporting subtitles and watches with the ripped DVD movie.
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