Setting Image Quality

Last updated: 2021-07-29 21:02:01

    Introduction

    In TRTCCloud, you can adjust the video quality in the following ways:

    This document describes how to configure these parameters to make the video quality of the TRTC SDK meet your project-specific needs.
    You can also see the following demos:

    Supported Platforms

    iOS Android Mac OS Windows Web Electron Flutter

    For detailed directions on how to set video quality for the Web, please see Configuration Guide.

    TRTCAppScene

    • VideoCall
      This corresponds to the scenario where most of the time there are two or more people on video calls, and the optimization for internal encoders and network protocols focuses on smoothness to reduce call latency and lagging.

    • LIVE
      This corresponds to the scenario where most of the time there is only one person speaking or performing and occasionally multiple people interact with one another through video, and the optimization for internal encoders and network protocols focuses on performance and compatibility to deliver better performance and definition.

    TRTCVideoEncParam

    Application Scenario videoResolution videoFps videoBitrate
    Video call (mobile) 640x360 15 550 Kbps
    Video conferencing (primary image on macOS or Windows) 1280x720 15 1,200 Kbps
    Video conferencing (primary image on mobile device) 640x360 15 900 Kbps
    Video conferencing (small image) 320x180 15 250 Kbps
    Online education (teacher on macOS or Windows) 960x540 15 850 Kbps
    Online education (teacher on iPad) 640x360 15 550 Kbps
    Online education (student) 320x180 15 250 Kbps

    Detailed description of fields

    • (TRTCVideoResolution) videoResolution
      Encoded resolution; for example, 640x360 refers to the width (pixels) x height (pixels) of the encoded video image. In the TRTCVideoResolution enum definition, only landscape resolution (i.e., width >= height) is defined. If you want to use portrait resolution, you need to set resMode to Portrait.

      Note:

      As many hardware codecs only support pixel widths that are divisible by 16, the actual resolution encoded by the SDK is not necessarily exactly the same as configured by the parameter; instead, it will be automatically corrected based on the divisor of 16; for example, the resolution 640x360 may be adapted to 640x368 inside the SDK.

    • (TRTCVideoResolutionMode) resMode
      This determines the landscape or portrait resolution. Because only landscape resolution is defined in TRTCVideoResolution, if you want to use portrait resolution such as 360x640, you need to specify resMode as TRTCVideoResolutionModePortrait. Generally, landscape resolution is used on PCs and Macs, while portrait resolution is used on mobile devices.

    • (int) videoFps
      Frame rate (FPS), which indicates how many frames are encoded per second. The recommended value is 15 FPS, which can ensure that the video image is smooth enough without reducing the video definition due to too many frames per second.

      If you have high requirements for smoothness, you can set the frame rate to 20 or 25 FPS. However, please do not set a value above 25 FPS, because the normal frame rate of movies is only 24 FPS.

    • (int) videoBitrate
      Video bitrate, which indicates how many Kbits of encoded binary data is output by the encoder per second. If you set videoBitrate to 800 Kbps, the encoder will generate 800 Kbits of video data per second. If such data is stored as a file, the file size will be 800 Kbits, which is 100 KB or 0.1 MB.

      A higher video bitrate is not always better; instead, it must have a proper mapping relationship with resolution as shown in the table below.

    Resolution-bitrate reference table

    Resolution Definition Aspect Ratio Recommended Bitrate High-end Configuration
    TRTCVideoResolution_120_120 1:1 80 Kbps 120 Kbps
    TRTCVideoResolution_160_160 1:1 100 Kbps 150 Kbps
    TRTCVideoResolution_270_270 1:1 200 Kbps 300 Kbps
    TRTCVideoResolution_480_480 1:1 350 Kbps 525 Kbps
    TRTCVideoResolution_160_120 4:3 100 Kbps 150 Kbps
    TRTCVideoResolution_240_180 4:3 150 Kbps 225 Kbps
    TRTCVideoResolution_280_210 4:3 200 Kbps 300 Kbps
    TRTCVideoResolution_320_240 4:3 250 Kbps 375 Kbps
    TRTCVideoResolution_400_300 4:3 300 Kbps 450 Kbps
    TRTCVideoResolution_480_360 4:3 400 Kbps 600 Kbps
    TRTCVideoResolution_640_480 4:3 600 Kbps 900 Kbps
    TRTCVideoResolution_960_720 4:3 1,000 Kbps 1,500 Kbps
    TRTCVideoResolution_160_90 16:9 150 Kbps 250 Kbps
    TRTCVideoResolution_256_144 16:9 200 Kbps 300 Kbps
    TRTCVideoResolution_320_180 16:9 250 Kbps 400 Kbps
    TRTCVideoResolution_480_270 16:9 350 Kbps 550 Kbps
    TRTCVideoResolution_640_360 16:9 550 Kbps 900 Kbps
    TRTCVideoResolution_960_540 16:9 850 Kbps 1,300 Kbps
    TRTCVideoResolution_1280_720 16:9 1,200 Kbps 1,800 Kbps

    TRTCNetworkQosParam

    QosPreference

    If the network bandwidth is sufficient, both high definition and smoothness can be ensured; however, if the user's network connection is not ideal, should priority be given to definition or smoothness? You can make a choice by specifying the preference parameter in TRTCNetworkQosParam.

    • Smoothness preferred (TRTCVideoQosPreferenceSmooth)
      Smoothness is ensured on a weak network, while the video image will have a lot of blurs but can be smooth with no or slight lagging.

    • Definition preferred (TRTCVideoQosPreferenceClear)
      Definition is ensured on a weak network, i.e., the image will be as clear as possible but tend to lag.

    ControlMode

    For the controlMode parameter, select TRTCQosControlModeServer. TRTCQosControlModeClient is used for internal debugging by the Tencent Cloud R&D team and should be ignored.

    Common Misunderstandings

    1. The higher the resolution, the better?
    Higher resolutions require higher bitrates for support. If the resolution is 1280x720, but the bitrate is specified as 200 Kbps, the video image will have a lot of blurs. We recommend that you set it as described in the Resolution-bitrate reference table.

    2. The higher the frame rate, the better?
    Because the image captured by the camera is a complete mapping to all real objects in the exposure phase, it is not that the higher the frame rate, the smoother the video, which is different from the concept of FPS in games. On the contrary, if the frame rate is too high, the quality of each video frame will be lowered, and the exposure time of the camera will be reduced, worsening the image effect.

    3. The higher the bitrate, the better?
    Higher bitrates also require higher resolutions for a match. For a resolution of 320x240, a 1,000 Kbps bitrate would be wasteful. We recommend that you set it as described in the Resolution-bitrate reference table.

    4. High resolution and bitrate can be set when connected to a Wi-Fi network?
    It is not that the Wi-Fi network speed is constant. If the device is far from the wireless router or the router channel is occupied, the Wi-Fi network may not be as fast as 4G.
    In response to this issue, the TRTC SDK provides a speed test feature, which can perform speed test to determine the network quality based on the score before a video call is established.