SetMediaNameToFilename

using System;
using Umbraco.Core;
using Umbraco.Core.Services;

namespace My.Namespace
{
    public class EventHandler : ApplicationEventHandler
    {
        protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            MediaService.Saving += SetMediaNameToFilename;
        }

        private void SetMediaNameToFilename(IMediaService sender, Umbraco.Core.Events.SaveEventArgs<Umbraco.Core.Models.IMedia> e)
        {
            foreach (var media in e.SavedEntities)
            {
                var filename = media.GetValue<string>("umbracoFile");
                if(string.IsNullOrWhiteSpace(filename))
                    return;

                filename = filename.Substring(filename.LastIndexOf("/", StringComparison.Ordinal) + 1);
                media.Name = filename;
            }
        }
    }
}