Exposing MP3 audio forgeries using frame offsets

Audio recordings should be authenticated before they are used as evidence. Although audio watermarking and signature are widely applied for authentication, these two techniques require accessing the original audio before it is published. Passive authentication is necessary for digital audio, especially for the most popular audio format: MP3. In this article, we propose a passive approach to detect forgeries of MP3 audio. During the process of MP3 encoding the audio samples are divided into frames, and thus each frame has its own frame offset after encoding. Forgeries lead to the breaking of framing grids. So the frame offset is a good indication for locating forgeries, and it can be retrieved by the identification of the quantization characteristic. In this way, the doctored positions can be automatically located. Experimental results demonstrate that the proposed approach is effective in detecting some common forgeries, such as deletion, insertion, substitution, and splicing. Even when the bit rate is as low as 32 kbps, the detection rate is above 99%.