  Multimodal manipulations (also known as audio-visual deepfakes) make it
difficult for unimodal deepfake detectors to detect forgeries in multimedia
content. To avoid the spread of false propaganda and fake news, timely
detection is crucial. The damage to either modality (i.e., visual or audio) can
only be discovered through multi-modal models that can exploit both pieces of
information simultaneously. Previous methods mainly adopt uni-modal video
forensics and use supervised pre-training for forgery detection. This study
proposes a new method based on a multi-modal self-supervised-learning (SSL)
feature extractor to exploit inconsistency between audio and visual modalities
for multi-modal video forgery detection. We use the transformer-based SSL
pre-trained Audio-Visual HuBERT (AV-HuBERT) model as a visual and acoustic
feature extractor and a multi-scale temporal convolutional neural network to
capture the temporal correlation between the audio and visual modalities. Since
AV-HuBERT only extracts visual features from the lip region, we also adopt
another transformer-based video model to exploit facial features and capture
spatial and temporal artifacts caused during the deepfake generation process.
Experimental results show that our model outperforms all existing models and
achieves new state-of-the-art performance on the FakeAVCeleb and DeepfakeTIMIT
datasets.
