目录

B-Frame Video Encoding

B-frame video encoding is supported from API version 20.

B-frames, short for Bidirectional Predictive Frames, are one of the primary frame types defined in video encoding standards. The main difference between B-frames and P-frames is that while P-frames support only forward prediction, B-frames support bidirectional prediction.

The prediction process in B-frame encoding utilizes information from both preceding and succeeding frames, which can significantly reduce temporal redundancy in the signal and achieve higher compression efficiency.

Enabling B-frames has the following impacts:

When to Use

Constraints

Available APIs

B-frame encoding must be configured at the initialization phase and takes effect throughout the process. Dynamic modification is not supported.

The configuration parameters are as follows:

Parameter Description Format
OH_MD_KEY_VIDEO_ENCODER_ENABLE_B_FRAME

Enabled status of B-frame video recording.

B-frame encoding can be enabled only when it is supported.

 int
OH_MD_KEY_VIDEO_ENCODER_MAX_B_FRAMES

Maximum number of B-frames supported by video encoding.

It is used only for query.

 int

How to Develop

For details about basic encoding functionality, see Video Encoding. The following are specific instructions for B-frame encoding.

  1. When creating an encoder instance, check whether the video encoder supports B-frame encoding.

    // 1.1 Obtain the video encoder capability instance. The following uses H.265 as an example.
OH_AVCapability *cap = OH_AVCodec_GetCapabilityByCategory(OH_AVCODEC_MIMETYPE_VIDEO_HEVC, true, HARDWARE);
if (cap != nullptr) {
    OH_LOG_INFO("Get codec Capability success!");
    // 1.2 Check whether B-frame encoding is supported.
    bool isSupported = OH_AVCapability_IsFeatureSupported(cap, VIDEO_ENCODER_B_FRAME);
    int32_t supportedMaxBFrameCount = 0;
    if (isSupported) {
        OH_LOG_INFO("Feature VIDEO_ENCODER_B_FRAME is Supported!");
        // 1.3 Query the maximum number of B-frames that can be supported.
        OH_AVFormat *property = OH_AVCapability_GetFeatureProperties(cap, VIDEO_ENCODER_B_FRAME);
        OH_AVFormat_GetIntValue(property, OH_MD_KEY_VIDEO_ENCODER_MAX_B_FRAMES, &supportedMaxBFrameCount);
        OH_LOG_INFO("Get supportedMaxBFrameCount,value is %{public}d!", supportedMaxBFrameCount);
        // 1.4 Destroy the temporary AVFormat.
        OH_AVFormat_Destroy(property);
    } else {
        OH_LOG_ERROR("Feature VIDEO_ENCODER_B_FRAME is not Supported!");
    }
} else {
    OH_LOG_ERROR("codec Capability is null!");
}

    If B-frame encoding is supported, you can enable it.

  2. Configure B-frame encoding during the configuration phase.

    // 2.1 Create a temporary AVFormat used for configuration.
OH_AVFormat *format = OH_AVFormat_Create();
// 2.2 Fill in the key-value pair of the parameter used to enable the feature.
OH_AVFormat_SetIntValue(format, OH_MD_KEY_VIDEO_ENCODER_ENABLE_B_FRAME, 1);
// 2.3 Set parameters.
int32_t ret = OH_VideoEncoder_Configure(videoEnc, format);
if (ret != AV_ERR_OK) {
    // Handle exceptions.
}
// 2.4 Destroy the temporary AVFormat after the configuration is complete.
OH_AVFormat_Destroy(format);
    • Enabling B-frame encoding is weakly checked during the configure phase. If the parameter configuration is incorrect or the encoder does not support the feature, AV_ERR_OK is returned, with a warning message printed. Check whether the feature is truly enabled based on the encoded stream and runtime logs.
    • When B-frame encoding is enabled, the actual B-frame structure and number of B-frames in the encoded stream depend on the platform's capabilities.