如何将 MP3Sharp 与 IFormFile 一起使用

Question

I want to convert an mp3 file to pcm using MP3Sharp ( https://github.com/ZaneDubya/MP3Sharp ) in a web app, where the mp3 file is passed in as IFormFile

It works if I save the file to disk first like this...

                using (Stream fileStream = new FileStream("file.mp3", FileMode.Create))
                {
                    await file.CopyToAsync(fileStream);
                }
                MP3Stream stream = new MP3Stream("file.mp3");

... but when I try to do it as a stream without writing to file it doesn't work:

                using (var fileStream = new MemoryStream())
                {
                    await file.CopyToAsync(fileStream);
                    MP3Stream stream = new MP3Stream(fileStream);
                }

The MP3Stream constructor throws this exception:

MP3Sharp.MP3SharpException: 'Unhandled channel count rep: -1 (allowed values are 1-mono and 2-stereo).'

... Any ideas on what I'm doing wrong?

Answer 1

After your code does file.CopyToAsync(fileStream) , the MemoryStream 's read/write position is pointing after the written MP3 data at the end of the MemoryStream .

The MP3Stream then trying to read from the MemoryStream will only notice that the end of the MemoryStream has been reached (because its read/write position is already at the end) and throws an exception. ^[1]

Thus, after copying the MP3 data into the MemoryStream , set the MemoryStream 's read/write position back to where it was before you copied the MP3 data into it (in the case of your example code it's the beginning of the MemoryStream , position 0):

await file.CopyToAsync(fileStream);
fileStream.Position = 0;

Side note: Like FileStream and MemoryStream , MP3Stream is also a Stream and therefore an IDisposable , too. And like you already did with the FileStream and the MemoryStream , you should use the using statement for the MP3Stream as well.

---

^[1] The exception you got from the MP3Sharp library is misleading, and as such is kind of a bug in the library. Because, when attempting to read a byte from a stream and the stream is at its end, the Stream.ReadByte method will return -1 to indicate end-of-stream. And as apparent by the exception message, it seems the MP3Sharp library does not properly treat the -1 value here as simply meaning " the end of the stream has been reached and no (further) data could be read " and misinterprets it as a channel count value.