--- title: Video input requirements slug: product-docs-v1/video-input-requirements description: Learn the necessary technical requirements for conducting a qualitative assessment of biometric parameters from a video. Discover the ideal camera specifications and video requirements such as lighting, subject position and video length. icon: 📹 docTags: createdAt: 2022-10-17T00:37:36.000Z --- In order to perform a **qualitative assessment** of the health parameters from a video, it is necessary to adhere to the following **input requirements **for the video recorded from the subject. As a commitment to maintaining a quality-first approach, we refrain from delivering results when accuracy cannot be guaranteed due to unmet input requirements. Our engine will return a clear *error\_code *in this case, explaining which input requirement was not met. A list of possible error\_codes can be found [here](docId\:ja-rra5kTYFj50zh-t2Xs). In these specific cases we advise to not abrubtly stop the end-user flow, but gracefully handle the error and inform the user on how to perform the measurement correctly. # Subject and environment ## Subject stillness and position It is important for the subject to **remain still during** the recording and **center the face **within the recording frame. The goal is to keep looking at the camera and minimize head movement. The setup is similar to when taking a photo. For comprehensive guidelines on how to correctly sit in front of the camera during the measurement, we refer to our [Usage instructions](docId\:ibtG0OD5eV7kfJmswyhnL). ## Lighting It is important to perform the recording in a well lit room. A lighting of at least **200 lux** is recommended. # Recording ## Video length The recording length of the video should be **at least 20 seconds** and should not exceed a length of one minute. A video length of **30 seconds** is **recommended**. :::BlockQuote A video length of 30 seconds provides a nice trade-off between accuracy, processing time and user experience. ::: Video's with a duration less then 20 seconds will not be processed. More info can be found here: [API docs > Get results > video too short](docId\:VH4BM6ywpiob981u8w6w2). ## Frame rate The video frame rate should at least be 30 fps and should not exceed 60 fps. The **recommended value** is a recording frame rate of **30 fps**. :::BlockQuote Higher frame rates may lead to a marginal increase in accuracy, but highly increases upload and processing time. ::: ## Resolution, Codec and Bitrate The video resolution, codec, and bitrate are critical properties to consider when capturing and processing video data for measuring the biomarkers using our algorithm. These factors play a vital role in preserving the necessary information about the blood volume pulse, which is essential for accurate measurements. - **Resolution**: ** between 320p and 1080p.** - **Codec**: **H264** or **H265** if supported; **VP8** when recording in most browsers. - **Bitrate**: depending on resolution and codec, see table below. :::ExpandableHeading **More info on why these parameters are important** Firstly, video resolution refers to the number of pixels contained in each frame of the video. Higher resolutions provide more detailed images, allowing for better visualization and analysis of subtle color variations in the skin. When measuring the blood volume pulse, these color differences are crucial for accurately detecting changes in blood flow and accurately determining values like heart rate and heart rate variability. Therefore, we recommend a **resolution between 320p and 1080p.** Secondly, the choice of codec, which determines how the video is compressed and encoded, can have an impact on the fidelity of the captured data. Some video codecs employ heavy compression techniques that can introduce artifacts or loss of detail in the video. It is important to select a codec that preserves color information and minimizes compression artifacts, as these artifacts can interfere with the accurate detection of subtle skin color changes. Codecs like** H.264** or **H.265 (HEVC) **are commonly used and provide good compression efficiency while maintaining reasonable video quality. When working with mobile devices and **recording the video in the browser**, we recommend the **VP8 codec, **which typically allows achieving higher framerates than alternative codecs. Lastly, the video bitrate plays a crucial role in determining the amount of data allocated to each second of video footage. Higher bitrates allow for more data to be captured and preserved, resulting in better representation of subtle color changes in the skin. Insufficient bitrate allocation can lead to loss of fine details, making it challenging to accurately extract the blood volume pulse signal. It is advisable to use higher bitrates when recording videos, especially if the intended application involves precise heart rate measurement. ::: Below you find a reference table with the ***minimal bitrate values*** (expressed in kbps) to which videos must comply. Mind that the minimal bitrate is both depending on the resolution and video codec. | Bitrate (kbps) | **H264** | **H265** | | -------------- | -------- | -------- | | **320p** | 4700 | 4030 | | **480p** | 1030 | 1280 | | **640p** | 2320 | 1540 | | **720p** | 1220 | 1940 | | **1080p** | 850 | 2890 | :::hint{type="info"} In case you are not sure the video is recorded correctly, we recommend using a tool like [https://www.metadata2go.com](https://www.metadata2go.com) to verify the video's metadata. The `r_frame_rate` field should contain a value between 30 and 60 fps. ::: ## Camera ### Camera sensor size & pixel size The camera sensor is the part of the imaging system that is sensitive to light. The size of this sensor plays an important role in the final quality of the image or video. The **larger the sensor**, the more **sensitive** it is **to** **light**. Larger image sensors have larger pixels, which means less noise, better dynamic range and the ability to obtain more (subtle) information. The **size of the sensor** should be at least **5.0 mm** in diagonal. The **size of a pixel** (unit cell) should be at least **1.0 μm**. :::BlockQuote These values are standard for most smart devices and laptops from the last 5 to 6 years. For example, the front camera of the Samsung Galaxy S6 from 2015 meets these requirements. ::: ### Lens quality Lens quality is becoming more important with the increasing pixel count on modern cameras. The resolution of digital photos is often limited by the camera lens rather than the resolution of the camera itself. In order to perform a qualitative measurement, the lens should have an **aperture** of at least **f2.8** and be **made from glass** or an (optically) higher quality material. :::BlockQuote Lenses of lower quality (e.g. plastic) may work, but this is not guaranteed, as these materials scratch up more easily and the optical quality varies greatly. :::