AVIAddXSubs is a simple to use, free program to subtitle videos converting the original srt files you may have. Its services are useful in cases your hardware player in not able to show the subtitles directly from srt or even if it does the result is not satisfactory. Using AVIAddXSubs and converting the srt you have a variety of options to configure the subtitles as regards font, font size, color, outline, position, etc. This effect is achieved through a srt conversion to another format where the subtitles are stored as bitmaps already prepared in your PC. There are two such formats you can use alternatively depending on what your player supports better.
1. The XSUB format where the generated bitmaps are presented as an additional stream inserted (or incorporated) in the video file itself. This works only with avi files. In this case another avi is generated that has the subtitles incorporated. Note that the input file for XSUB conversion can be in idx/sub format too, additionally to srt.
2. The idx/sub format. This format uses a pair of files, one with extension idx and another with extension sub. These files go together and replace the srt in your player. Using idx/sub, because are external files (that is, not incorporated), you can subtitle any kind of video file. avi/mkv/mp4, you name it.