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Hardware video accelerators are used on mobile devices to provide support for energy efficient real time High definition (HD) video decoding. Recently, the rise of multi-core archi-tectures on those devices increased their performances and make real time HD video decoding possible using parallel processing on the GPP cores only. What is even more in-teresting to know is the level of energy efficiency these kind of multi-core General Purpuse Processor (GPP) can achieve as compared to hardware video accelerators. In this paper, we propose an experimental evaluation of the energy effi-ciency of the two video decoding approaches. An accurate energy measurement was achieved on a recent low-power 40 nm mobile SoC containing a quad-core ARM processors and a video hardware accelerator. The results show that parallel multi-core HD decoding enhances both the performance and the energy efficiency as compared to the use of a single core. However, the hardware accelerated decoding is about three times more energy efficient. Based on the experimental ob-servations, some challenges for enhancing parallel multi-core video decoding energy efficiency are pointed out