With the growing popularity of short-form video sharing platforms such as Instagram and Vine , there has been an increasing need for techniques that automatically extract highlights from video. Whereas prior works have approached this problem with heuristic rules or supervised learning, we present an unsupervised learning approach that takes advantage of the abundance of user-edited videos on social media websites such as YouTube. Based on the idea that the most significant sub-events within a video class are commonly present among edited videos while less interesting ones appear less frequently, we identify the significant sub-events via a robust recurrent auto-encoder trained on a collection of user-edited videos queried for each particular class of interest. The auto-encoder is trained using a proposed shrinking exponential loss function that makes it robust to noise in the web-crawled training data, and is configured with bidirectional long short term memory (LSTM) LSTM:97 cells to better model the temporal structure of highlight segments. Different from supervised techniques, our method can infer highlights using only a set of downloaded edited videos, without also needing their pre-edited counterparts which are rarely available online. Extensive experiments indicate the promise of our proposed solution in this challenging unsupervised settin
@cite_36: Acoustic novelty detection aims at identifying abnormal novel acoustic signals which differ from the reference normal data that the system was trained with. In this paper we present a novel unsupervised approach based on a denoising autoencoder. In our approach auditory spectral features are processed by a denoising autoencoder with bidirectional Long Short-Term Memory recurrent neural networks. We use the reconstruction error between the input and the output of the autoencoder as activation signal to detect novel events. The autoencoder is trained on a public database which contains recordings of typical in-home situations such as talking, watching television, playing and eating. The evaluation was performed on more than 260 different abnormal events. We compare results with state-of-theart methods and we conclude that our novel approach significantly outperforms existing methods by achieving up to 93.4 F-Measure.
The one-class learning of our recurrent auto-encoder is related to works on novelty detection, which aim to identify outliers from an observed class. In @cite_36 , novelty detection is performed for audio features using an auto-encoder with LSTM. Our concurrent work deals instead with RGB video data, for which meaningful features are more challenging to extract. We address this through temporal video segmentation, extraction of high-level spatial-temporal features for each segment, and then temporal pooling, before feeding to the auto-encoder. Moreover, we introduce a novel shrinking loss function to address the noisy training data in our context.