I am using SubEdit to convert a *.srt subtitle file to *.sub (MicroDVD) subtitle and after conversion, the *.sub seems to be out of sync. To verify this, I tried to convert the *.sub file to *.srt file, then, surprisingly, the *.srt is also different from the original *.srt file (I expected the 2 *.srt file MUST be the same, otherwise, there is something wrong with the conversion). See below screenshot. Please help and thank you very much.
[Attachment 47004 - Click to enlarge]
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It looks to me like the difference is only because video has discreet frames at fixed intervals. Those intervals do not necessarily match the millisecond increments in which SRT subs are specified. In other words, the granularity of subtitle timing in the source SRT file is 1/1000 second. The granularity of subtitle timing in the SUB file is frame number (1/23.976 seconds). So a round trip from SRT to SUB to SRT will not preserve the timing exactly.
If you have a longer term drift it may be because the frame rate assumed for the SUB video. Eg, 23.976 fps rather than 25 fps.