Upload to File column on Track record

// Upload the file to the newly created Track record
function uploadFile(fileContent,fileName,entityID) {
    var record = {};
    record.musdyn_name = fileName;

    webapi.safeAjax({
        type: "PUT", // NOTE: right now Portals requires PUT instead of PATCH for the upload
        url: "/_api/musdyn_tracks(" + entityID + ")/musdyn_audiotrack?x-ms-file-name=" + fileName,
        contentType: "application/octet-stream",
        data: fileContent,
        processData: false,
        success: function (data, textStatus, xhr) {
            // Provide some visual feedback re successful upload
            $('#upload-Audio h1').html('<span style="color: #1ed760;" class="glyphicon glyphicon-ok"></span> Here\'s your audio');
            // Set the source of the hidden audio player
            audioPlayerSrcURL = '/File/download.aspx?Entity=musdyn_track' + '&Attribute=musdyn_audiotrack&Id=' + entityID;
            $('#upload-player').attr('src',audioPlayerSrcURL)
            // Show the audio player
            $('.showOnSuccess').slideDown(200);
            // Hide the form
            $('#track-content').slideUp(200);
        },
        error: function (xhr, textStatus, errorThrown) {
            // If error occurs uploading the file, provide visual feedback
            $('#upload-Audio h1').text('Uh oh, uploading file the track');
        }
    });
}