xcode ios swift视频压缩使用hevc编码

通常苹果的hdr视频都是使用hevc编码的，且支持hevc的播放器一般都支持hdr播放，所以压缩视频的时候选择hevc编码也很合理。

1.压缩的时候需要设置两个属性 AVVideoCodecKey

因为压缩的时候AVVideoCodecKey属性是必须要设置的，点进AVVideoCodecKey的头文件中，描述为：

extension AVVideoCodecType {

    
    @available(iOS 11.0, *)
    public static let hevc: AVVideoCodecType

    @available(iOS 11.0, *)
    public static let h264: AVVideoCodecType /* @"avc1" */

    @available(iOS 11.0, *)
    public static let jpeg: AVVideoCodecType /* @"jpeg" */

    @available(iOS 11.0, *)
    public static let proRes4444: AVVideoCodecType /* @"ap4h" */

    @available(iOS 11.0, *)
    public static let proRes422: AVVideoCodecType /* @"apcn" */

    @available(iOS 13.0, *)
    public static let proRes422HQ: AVVideoCodecType /* @"apch" */

    @available(iOS 13.0, *)
    public static let proRes422LT: AVVideoCodecType /* @"apcs" */

    @available(iOS 13.0, *)
    public static let proRes422Proxy: AVVideoCodecType /* @"apco" */

    
    /* IMPORTANT NOTE: this constant is used to select the appropriate encoder, but is NOT used on the encoded content, which is backwards compatible and hence uses 'hvc1' as its codec type. */
    @available(iOS 13.0, *)
    public static let hevcWithAlpha: AVVideoCodecType /* @"muxa" */
}

直接选择hevc即可

AVVideoProfileLevelKey

并且要同时设置AVVideoProfileLevelKey，点进去只看到H264的Value值，而我们需要的hevc不在里面，但是有段注释

/* HEVC profiles/levels are defined in 
VideoToolbox/VTCompressionProperties.h, e.g. 
kVTProfileLevel_HEVC_Main_AutoLevel. The constants
 defined there can be used as the value for the key 
AVVideoProfileLevelKey. */

意思就是hevc在“VideoToolbox/VTCompressionProperties.h”里面定义的
所以需要在使用hevc编码的时候导入头文件

import VideoToolbox

总结

exportSession.videoSettings = [
	//这里设置编码格式
	AVVideoCodecKey: AVVideoCodecType.hevc,
	//长
	AVVideoWidthKey: targetSize.width,
	//宽
	AVVideoHeightKey: targetSize.height,
	AVVideoCompressionPropertiesKey: [
		//长*宽*三原色
		AVVideoAverageBitRateKey: targetSize.width * targetSize.height * 3,
		//这里要和上面配套设置为hevc，不然会报错，并且需要在代码中引入import VideoToolbox
		AVVideoProfileLevelKey: kVTProfileLevel_HEVC_Main10_AutoLevel,
	],
]