iOS HDR转SDR-解决iPhone12视频在chrome白平衡异常问题

标题有点长, 因为一直没想好怎样简洁的表述这个问题

问题现象: iPhone12拍摄的视频上传到服务器后, 在chrome, ie等浏览器播放会泛白

问题原因: 因为iPhone12默认拍摄杜比视界HDR高动态范围视频, chrome, ie的色彩管理有点问题, 在非HDR显示器显示时候, 还是按照HDR范围显示, 导致色彩出现"过曝"现象

解决方案: 对视频进行转码. 指定色彩管理配置

核心代码:

inline static NSDictionary *lf_assetExportVideoConfig(CGSize size, LFAssetExportSessionPreset preset)
{
    float ratio = 1;
    CGSize presetSize = lf_assetExportSessionPresetSize(preset);
    CGSize videoSize = size;
    if (videoSize.width > videoSize.height) {
        ratio = videoSize.width / presetSize.height;
    } else {
        ratio = videoSize.width / presetSize.width;
    }
    
    if (ratio > 1) {
        videoSize = CGSizeMake(videoSize.width / ratio, videoSize.height / ratio);
    }
    if (@available(iOS 10.0, *)) {
        return @{
            AVVideoCodecKey: AVVideoCodecH264,
            AVVideoWidthKey:[NSNumber numberWithInteger:videoSize.width],
            AVVideoHeightKey:[NSNumber numberWithInteger:videoSize.height],
            AVVideoScalingModeKey:AVVideoScalingModeResizeAspectFill,
            AVVideoCompressionPropertiesKey: @
            {
                ///选择视频颜色编码格式(默认格式会支持HDR, 导致视频在chrome, ie泛白)
                ///默认为: AVVideoYCbCrMatrix_ITU_R_2020, 为支持HDR的格式, 应当指定为ITU_R_709_2通用配置
                AVVideoColorPrimariesKey : AVVideoColorPrimaries_ITU_R_709_2,
                AVVideoAverageBitRateKey: [NSNumber numberWithUnsignedLong:lf_assetExportSessionPresetBitrate()],
                AVVideoProfileLevelKey: AVVideoProfileLevelH264HighAutoLevel,
                AVVideoAllowFrameReorderingKey:@NO,
                AVVideoExpectedSourceFrameRateKey:@24
            },
        };
    } else {
        return @{
            AVVideoCodecKey: AVVideoCodecH264,
            AVVideoWidthKey:[NSNumber numberWithInteger:videoSize.width],
            AVVideoHeightKey:[NSNumber numberWithInteger:videoSize.height],
            AVVideoScalingModeKey:AVVideoScalingModeResizeAspectFill,
            AVVideoCompressionPropertiesKey: @
            {
                AVVideoAverageBitRateKey: [NSNumber numberWithUnsignedLong:lf_assetExportSessionPresetBitrate()],
                AVVideoProfileLevelKey: AVVideoProfileLevelH264HighAutoLevel,
                AVVideoAllowFrameReorderingKey:@NO,
                AVVideoExpectedSourceFrameRateKey:@24
            },
        };
    }
}

简单总结下:
因为我们这边业务需求是用户上传的视频需要在本地做一次压缩, 我这边采用的方案就是AVAssetExportSession逐帧压缩. 在输出配置里面指定色彩配置即可(即强制把HDR视频转换成SDR视频).

效果如下:

HDR原视频效果

SDR视频效果