OMA is an audio format developed by Sony. It is an implementation of ATRAC standard that offers Audio CD quality and up to 20 times smaller files. OMA files were popular as the standard audio encoding used by MiniDisc (MD) standard, which never gained significant popularity.
MP3 is short for MPEG-1 Audio Layer-3 and is probably the most popular audio data file format in the world. This compressed audio format was created in early 1990s by Moving Picture Experts Group (MPEG).
After converting the file to the new format, you will be able to use other programs to support it. Keep in mind, however, that the OMA file after converting to MP3 may differ slightly from the original. The most important information should be kept, but if you want the file after conversion from OMA to MP3 to be the same, you have to do this carefully and choose the proper application from the list below.
There is no guarantee, of course, that the conversion will come up to all your expectations, but it will certainly help you. If, after all, the effect of converting OMA to MP3 does not meet your expectations, you can simply try to find on the Internet a different version of your file in OMA format, properly converted to a MP3 file by someone else. If this fails, use the information provided in the further part of the website.
Unfortunately, if after performing the two previously described steps (trying to find your OMA file converted by someone else, and the attempt to convert it to MP3 on your own) you still have a problem with your file, then there are only a few solutions left. You can once again try to find and install an application that can open the OMA file in its original format (without conversion to MP3 file). Such a solution will be difficult to implement, but it certainly will give the best result.