The ever-increasing Internet distribution of video content is echoed in ever-increasing efforts to devise systems balancing copyright protection and user rights. Watermarking is such an example: by persistently and imperceptibly associating some data with the host video, it offers at the same time a reliable and user-friendly solution for copyright infringement tracking. This paper takes a closer look at the apparent contradiction between watermarking (using the visual redundancy of the video to embed the data) and compression (eliminating the visual redundancy in order to speed up distribution and to alleviate storage requirements). In this respect, the viability of compressed domain watermarking is evaluated by analysing the visual effects of the MPEG-4 AVC stream alteration. The corpus consists of 10 video sequences of about 25 minutes each, coded at 256kbps and 64 kbps