A couple of weeks ago I started to notice that I couldn’t watch videos served via my Samba server on my MacBook. I first thought it was a problem with Quicktime Player, but later I tried VLC and the problem was still there. I started up Activity Monitor to see how fast was the download speed, it was hardly over 150KB/s. Before, I was able to watch flawlessly on my MacBook with download speed of up to 2MB/s. Initially I thought that this could have something to do with the recent security updates of Mac OS X, but I couldn’t find anyone having the same problem on Google. Later I tried mounting my Windows-powered laptop’s shared folder and initiated a file transfer to my MacBook, it was transferring at normal speed (2MB/s)! So this problem only occurs when the share is served off Samba.
Yesterday I tried my luck on Google once more and finally I found this (sudo sysctl -w net.inet.tcp.delayed_ack=0). Applied the suggested solution and it worked! Case closed.