This paper describes the analysis, in terms of tolerance to errors on data, of a H.264 software video encoder; proposes a strategy to select data structures for approximate memory allocation and reports the impact on output video quality. Applications that tolerate errors on their data structures are known as ETA (Error Tolerant Applications) and have an important part in pushing interest on approximate computing research. We centered our study on H.264 video encoding, a video compression format developed for use in high definition systems, and today one of the most widespread video compression standard, used for broadcast, consumer and mobile applications. While data fault resilience of H.264 has already been studied considering unwanted and random faults due to unreliable hardware platforms, an analysis, considering controlled hardware faults and the corresponding energy quality tradeoff, has never been proposed.