Pinecast does not transcode your audio after you have uploaded it. We will never re-encode your audio files without your explicit instruction or permission.
When uploading files, you may be prompted to add metadata or episode artwork. We will modify your MP3 file to add the appropriate ID3 tags. This physically modifies the file, but a non-corrupt file should not be negatively affected in any way. If ID3 tags are added, existing tags will be overwritten.