Recommendation ITU-T P.1204 provides the introductory document for a set of documents that describe model algorithms for monitoring the video quality for streaming using reliable transport (e.g. HTTP-based adaptive streaming over TCP, QUIC). The standard comprises different variants of models for sequence-related (between 5 and 10 sec.) and per-1-second video-quality estimation. The variants differ in the type of input information they use: Bitstream-based, pixel-based, and hybrid (using both bitstream and pixel information). In principle, the per-1-second outputs of these video-quality models can be used together with an audio-quality model for integration into audiovisual quality and, together with information about initial loading delay and media playout stalling events, further into a final per-session model output, an estimate of integral per-session quality (see e.g. ITU-T Recs. P.1203, P.1203.2, P.1203.3). The respective ITU-T work item has formerly been referred to as "P.NATS Phase 2", and was conducted in collaboration between ITU-T Study Group 12 and the Video Quality Experts Group (VQEG). The structure of the set of recommendations reflects the different functionality of modules described in each document: -ITU-T P.1204: Introductory document (this Recommendation) -DRAFT P.1204.1: Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to transport information (under development) -DRAFT P.1204.2: Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to video frame information (under development) -ITU-T P.1204.3: Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to full bitstream information -ITU-T P.1204.4: Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to full and reduced reference pixel information -ITU-T P.1204.5: Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to transport and received pixel information The ITU-T P.1204-series of Recommendations addresses three application areas, which are respectively indicated in the module-related P.1204.1 (draft, under development), P.1204.2 (draft, under development), and Recommendations ITU-T P.1204.3, ITU-T P.1204.4, ITU-T P.1204.5: -Large-screen presentation as with fixed-network video streaming -Mobile streaming on handheld devices such as smartphones -Presentation on tablet-type devices