Nero Recode Video sources come from two parts: disc and single video file.
1) Disc as Source:
According to DVD specifications, DVD disc includes BUP, IFO, VOB files. There are video, sound, and subtitle streams in the VOB file. IFO is an index file, which tells the VOB file when and where to appear subtitles. If the user only imports a single VOB file from disc, Recode can read the subtitle stream through the exif information of the VOB, and the language option will be listed on the Recode interface. But when Recode starts transcoding, It cannot find the corresponding IFO index in VOB file, so it will discard the subtitles.
If the user imports the entire DVD disc, user can only see the title (in fact, due to the complexity of the disc structure, a title may include multiple VOBs, or a title may be scattered in different VOB files), but IFO files and other information are also read in the background. When transcodes MKV, Recode will obtain the index information of IFO, and then copy the subtitles to the corresponding location, so that the transcoded file has subtitle information. Therefore, it is recommended for users to import the entire disk, and then select the desired title to generate a video file with subtitles.
2) If source is single video, there are two scenarios:
1. Subtitles are included in files, such as MP4, MKV files: Subtitles and videos are combined, so the subtitles will not be lost after transcoding.
2. The subtitles saved in the .srt or ass file: When playing video with a player that supports srt/ass file, the player can locate the time stamp and matched subtitles to video, but because Recode cannot support srt or ass, the subtitles will not appear in the preview and transcoding result.