Abstract
This column introduces the now completed ITU-T P.1204 video quality model standards for assessing sequences up to UHD/4K resolution. Initially developed over two years by ITU-T Study Group 12 (Question Q14/12) and VQEG, the work used a large dataset of 26 subjective tests (13 for training, 13 for validation), each involving at least 24 participants rating sequences on the 5-point ACR scale. The tests covered diverse encoding settings, bitrates, resolutions, and framerates for H.264/AVC, H.265/HEVC, and VP9 codecs. The resulting 5,000-sequence dataset forms the largest lab-based source for model development to date. Initially standardized were P.1204.3, a no-reference bitstream-based model with full bitstream access, P.1204.4, a pixel-based, reduced-/full-reference model, and P.1204.5, a no-reference hybrid model. The current record focuses on the latest additions to the series, namely P.1204.1, a parametric, metadata-based model using only information about which codec was used, plus bitrate, framerate and resolution, and P.1204.2, which in addition uses frame-size and frame-type information to include video-content aspects into the predictions.
Introduction
Video quality under specific encoding settings is central to applications such as VoD, live streaming, and audiovisual communication. In HTTP-based adaptive streaming (HAS) services, bitrate ladders define video representations across resolutions and bitrates, balancing screen resolution and network capacity. Video quality, a key contributor to users’ Quality of Experience (QoE), can vary with bandwidth fluctuations, buffer delays, or playback stalls.
While such quality fluctuations and broader QoE aspects are discussed elsewhere, this record focuses on short-term video quality as modeled by ITU-T P.1204 for HAS-type content. These models assess segments of around 10s under reliable transport (e.g., TCP, QUIC), covering resolution, framerate, and encoding effects, but excluding pixel-level impairments from packet loss under unreliable transport.
Because video quality is perceptual, subjective tests, laboratory or crowdsourced, remain essential, especially at high resolutions such as 4K UHD under controlled viewing conditions (1.5H or 1.6H viewing distance). Yet, studies show limited perceptual gain between HD and 4K, depending on source content, underlining the need for representative test materials. Given the high cost of such tests, objective (instrumental) models are required for scalable, automated assessment supporting applications like bitrate ladder design and service monitoring.
Four main model classes exist: metadata-based, bitstream-based, pixel-based, and hybrid. Metadata-based models use codec parameters (e.g., resolution, bitrate) and are lightweight; bitstream-based models analyze encoded streams without decoding, as in ITU-T P.1203 and P.1204.3 [1][2][3][7]. Pixel-based models compare decoded frames and include Full Reference and Reduced Reference models (e.g., P.1204.4, and also PSNR [9], SSIM [10], VMAF [11][12]), as well as No Reference variants. Finally, hybrid models combine pixel and bitstream or metadata inputs, exemplified by the ITU-T P.1204.5 standard. These three standards, P.1204.3 P.1204.4 and P.1204.5, formed the initial P.1204 Recommendation series finalized in 2020.
ITU-T P.1204 series completed with P.1204.1 and P.1204.2
The respective standardization project under the Work Item name P.NATS Phase 2 (read: Peanuts) was a unique video quality model development competition conducted in collaboration between ITU-T Study Group 12 (SG12) and the Video Quality Experts Group (VQEG). The target use cases were for up to UHD/4K resolution, with presentation on UHD/4K resolution PC/TV or Mobile/Tablet (MO/TA). For the first time, bitstream-, pixel-based, and hybrid models were jointly developed, trained, and validated, using a large common subjective dataset comprising 26 tests, each with at least 24 participants (see, e.g., [1] for details). The P.NATS Phase 2 work built on the earlier “P.NATS Phase 1” project, which resulted in the ITU-T Rec. P.1203 standards series (P.1203, P.1203.1, P.1203.2, P.1203.3). In the P.NATS Phase 2 project, video quality models in five different categories were evaluated, and different candidates were found to be eligible to be recommended as standards. The initially standardized three models out of the five categories were the aforementioned P.1204.3, P.1204.4 and P.1204.5. However, due to the lack of consensus between the winning proponents, no models were recommended as standards for the category “bitstream Mode 0” with access to high-level metadata only, such as the video codec, resolution, framerate and bitrate used, and “bitstream Mode 1”, with further access to frame-size information that can be used for content-complexity estimation.
For the latest model additions of P.1204.1 and P.1204.2, subsets of the databases initially used in the P.NATS Phase 2 project were employed for model training. Two different datasets belonging to the two contexts PC/TV and MO/TA were used for training the models. AVT-PNATS-UHD-1 is the dataset for the PC/TV use case and ERCS-PNATS-UHD-1 the dataset used for the MO/TA use case.
AVT-PNATS-UHD-1 [7] consists of four different subjective tests conducted by TU Ilmenau as part of the P.NATS Phase 2 competition. The target resolution of these datasets was 3840 x 2160 pixels. ERCS-PNATS-UHD-1 [1] is a dataset targeting the MO/TA use case. It consists of one subjective test conducted by Ericsson as part of the P.NATS Phase 2 competition. The target resolution of these datasets was 2560 x 1440 pixels.
For model performance evaluation, beyond AVT-PNATS-UHD-1, further externally available video-quality test databases were used, as outlined in the following.
AVT-VQDB-UHD-1: This is a publicly available dataset and consists of four different subjective tests. All the four tests had a full-factorial design. In total, 17 different SRCs with a duration of 7-10 s were used across all the four tests. All the sources had a resolution of 3840×2160 pixels and a framerate of 60 fps. For HRC design, bitrate was selected in fixed (i.e. non-adaptive) values per PVS between 200kbps and 40000kbps, resolution between 360p and 2160p and framerate between 15fps and 60fps. In all the tests, a 2-pass encoding approach was used to encode the videos, with medium preset for H.264 and H.265, and the speed parameter for VP9 set to the default value “0”. A total of 104 participants in the four tests.
GVS: This dataset consists of 24 SRCs that have been extracted from 12 different games. The SRCs are of 1920×1080 pixel resolution, 30fps framerate and have a duration of 30s . The HRC design included three different resolutions, namely, 480p, 720p and 1080p . 90 PVSs resulting from 15 bitrate-resolution pairs were used for subjective evaluation. A total of 25 participants rated all the 90 PVSs.
KUGVD: Six SRCs out of the 24 SRCs from the GVSwere used to develop KUGVD. The same bitrate-resolution pairs from GVS were included to define the HRCs. In total, 90 PVSs were used in the subjective evaluation and 17 participants took part in the test.
CGVDS: This dataset consists of SRCs captured at 60fps from 15 different games. For designing the HRCs, three resolutions, namely, 480p, 720p and 1080p at three different framerates of 20, 30, and 60fps were considered. To ensure that the SRCs from all the games could be assessed by test subjects, the overall test was split into 5 different subjective tests, with a minimum of 72 PVSs being rated in each of the tests. A total of over 100 participants took part over the five different tests, with a minimum of 20 participants per test.
Twitch: The Twitch Dataset consists of 36 different games, with 6 games each representing one out of 6 pre-defined genres. The dataset consists of streams directly downloaded from Twitch. A total of 351 video sequences of approximately 50s duration across all representations were downloaded. 90 video sequences out of these 351 video sequences were selected for subjective evaluation. Only the first 30s of the chosen 90 PVSs were considered for subjective testing. Six different resolutions between 160p and 1080p at framerates of 30 and 60fps were used. 29 participants rated all the 90 PVSs.
BBQCG: This is the training dataset developed as part of the P.BBQCG work item. This dataset consists of nine subjective test databases. Three out of these nine test databases consisted of processed video sequences (PVSs) up to 1080p/120fps and the remaining had PVSs up to 4K/60fps. Three codecs, namely, H.264, H.265, and AV1 were used to encode the videos. Overall 900 different PVSs were created from 12 sources (SRCs) by encoding the SRCs with different encoding settings.
AVT-VQDB-UHD-1-VD: This dataset consists of 16 source contents encoded using a CRF-based encoding approach. Overall 192 PVSs were generated by encoding all 16 sources in four resolutions, namely, 360p, 720p, 1080p, 2160p with three CRF values (22, 30, 38) each. A total of 40 subjects participate in the study.
ITU-T P.1204.1 and P.1204.2 model prediction performance
The performance figures of the two new models P.1204.1 and P.1204.2 models on the different datasets are indicated in Table 1 (P.1204.1) and Table 2 (P.1204.2) below.
| Dataset | RMSE | PCC | SRCC | Kendall |
| AVT-VQDB-UHD-1 | 0.499 | 0.890 | 0.877 | 0.684 |
| KUGVD | 0.840 | 0.590 | 0.570 | 0.410 |
| GVS | 0.690 | 0.670 | 0.650 | 0.490 |
| CGVDS | 0.470 | 0.780 | 0.750 | 0.560 |
| Twitch | 0.430 | 0.920 | 0.890 | 0.710 |
| BBQCG | 0.598 (on a 7-point scale) | 0.841 | 0.843 | 0.647 |
| AVT-VQDB-UHD-1-VD | 0.650 | 0.814 | 0.813 | 0.617 |
| Dataset | RMSE | PCC | SRCC | Kendall |
| AVT-VQDB-UHD-1 | 0.476 | 0.901 | 0.900 | 0.730 |
| KUGVD | 0.500 | 0.870 | 0.860 | 0.690 |
| GVS | 0.420 | 0.890 | 0.870 | 0.710 |
| CGVDS | 0.360 | 0.900 | 0.880 | 0.690 |
| Twitch | 0.370 | 0.940 | 0.930 | 0.770 |
| BBQCG | 0.737 (on a 7-point scale) | 0.745 | 0.746 | 0.547 |
| AVT-VQDB-UHD-1-VD | 0.598 | 0.845 | 0.845 | 0.654 |
For all databases except BBQCG and KUGVD, the Mode 0 model P.1204.1 performs in a solid way, as shown in Table 1. With the information about frame types and sizes available to the Mode 1 model P.1204.2, performance improves considerably, as shown in Table 2. For performance results of all three previously standardized models, P.1204.3, P.1204.4 and P.1204.5, the reader is referred to [1] and the individual standards, [4][5][6]. For the P.1204.3 model, complementary performance information is presented in, e.g., [2][7]. For P.1204.4, additional model performance information is available in [8], including results for AV1, AVS2, and VVC.
The following plots provide an illustration of how the new P.1204.1 Mode 0 model may be used. Here, bitrate-ladder-type graphs are presented, with the predicted Mean Opinion Score on a 5-point scale plotted over log bitrate.
![]() Codec: H.264 | ![]() Codec: H.265 | ![]() Codec: VP9 |
Conclusions and Outlook
The P.1204 standard series now comprises the complete initially planned set of models, namely:
- ITU-T P.1204.1: Bitstream Mode 0, i.e., metadata-based model with access to information about video codec, resolution, framerate and bitrate used.
- ITU-T P.1204.2: Bitstream Mode 1, i.e., metadata-based model with access to information about video codec, resolution, framerate and bitrate used, plus information about video frame types and sizes.
- ITU-T P.1204.3: Bitstream Mode 3 [1][2][3][7].
- ITU-T P.1204.4: Pixel-based reduced- and full-reference [1][5][8].
- ITU-T P.1204.5: Hybrid no-reference Mode 0 [1][6].
Extensions of some of these models beyond the initial scope of codecs (H.264/AVC, H.265/HEVC, VP9) have been included over the last few years. Here, P.1204.4 and P.1204.5 have been extended (P.1204.5) or evaluated (P.1204.4) to also cover the AV1 video codec. Work in ITU-T SG12 (Q14/12) is ongoing so as to also extend P.1204.1, P.1204.2 and P.1204.3 to newer codecs such as AV1, and all five models are planned to be extended so as to also cover VVC. It is noted that for P.1204.3, P.1204.4 and P.1204.5, also long-term quality integration modules that generate per-session scores for up to 5min long streaming sessions have been described in Appendices of the respective recommendations. For P.1204.1 and P.1204.2, this extension still has to be completed. Initial evaluations for similar Mode 0 and Mode 1 models that use the P.1204.3-type long-term integration can be found in [7].
References
[1] Raake, A., Borer, S., Satti, S.M., Gustafsson, J., Rao, R.R.R., Medagli, S., List, P., Göring, S., Lindero, D., Robitza, W. and Heikkilä, G., 2020. Multi-model standard for bitstream-, pixel-based and hybrid video quality assessment of UHD/4K: ITU-T P. 1204. IEEE Access, 8, pp.193020-193049.
[2] Rao, R.R.R., Göring, S., List, P., Robitza, W., Feiten, B., Wüstenhagen, U. and Raake, A., 2020, May. Bitstream-based model standard for 4K/UHD: ITU-T P. 1204.3—Model details, evaluation, analysis and open source implementation. In 2020 Twelfth International Conference on Quality of Multimedia Experience (QoMEX) (pp. 1-6).
[3] ITU-T Rec. P.1204, 2025. Video quality assessment of streaming services over reliable transport for resolutions up to 4K. International Telecommunication Union (ITU-T), Geneva, Switzerland.
[4] ITU-T Rec. P.1204.3, 2020. Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to full bitstream information. International Telecommunication Union (ITU-T), Geneva, Switzerland.
[5] ITU-T Rec. P.1204.4, 2022. Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to full and reduced reference pixel information. International Telecommunication Union (ITU-T), Geneva, Switzerland.
[6] ITU-T Rec. P.1204.5, 2023. Video quality assessment of streaming services over reliable transport for resolutions up to 4K with access to transport and received pixel information. International Telecommunication Union (ITU-T), Geneva, Switzerland.
[7] Rao, R.R.R., Göring, S. and Raake, A., 2022. AVQBits – Adaptive video quality model based on bitstream information for various video applications. IEEE Access, 10, pp.80321-80351.
[8] Borer, S., 2022, September. Performance of ITU-T P. 1204.4 on Video Encoded with AV1, AVS2, VVC. In 2022 14th International Conference on Quality of Multimedia Experience (QoMEX) (pp. 1-4).
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[10] Wang, Z., Lu, L. and Bovik, A.C., 2004. Video quality assessment based on structural distortion measurement. Signal Processing: Image Communication, 19(2), pp.121-132.
[11] Li, Z., Aaron, A., Katsavounidis, I., Moorthy, A., and Manohara, M., 2016. Toward A Practical Perceptual Video Quality Metric, Netflix TechBlog.
[12] Li, Z., Swanson, K., Bampis, C., Krasula, L., and Aaron, A., 2020. Toward a Better Quality Metric for the Video Community, Netflix TechBlog.































