Estimating video resolution delivered by an encrypted video stream

A network node, or a group of nodes of a network, configured with access to data packets carrying an encrypted video stream being communicated through the network, the network node, or each of the group of nodes comprising a processor and a memory, the memory storing instructions executable by the processor thereby to configure the network node, or group of network nodes, to access data packets carrying an encrypted video stream being communicated through the network and to estimate playout resolution of a video delivered to a client device by the encrypted video stream by:

• (i) obtaining a first probability distribution for a plurality of states of a Markov chain, the states comprising a plurality of different levels of playout resolution that may be achieved at the client device by the delivered video stream;
• (ii) selecting a current chunk of the encrypted video stream comprising data packets expected to carry video data of the same level of playout resolution;
• (iii) by analysis of the data packets in the selected current chunk, determining values for features in a predetermined set of features indicative of conditions in the network;
• (iv) using a pre-generated model to obtain, given the determined set of feature values from (iii), a corresponding set of state transition probabilities of the Markov chain;
• and
• (v) applying the determined state transition probabilities from (iv) to calculate, from the first probability distribution obtained at (i), a second probability distribution for the plurality of states of the Markov chain, thereby for the plurality of different levels of playout resolution expected to result from the indicated network conditions.