Question

我现在正在使用Videotoolbox来处理h.264编码。

我找到了一个示例代码，它运行正常：

    #define VTB_HEIGHT 480
    #define VTB_WIDTH 640

    int bitRate = VTB_WIDTH * VTB_HEIGHT * 3 * 4 * 8;

    CFNumberRef bitRateRef = CFNumberCreate(kCFAllocatorDefault,
                                            kCFNumberSInt32Type,
                                            &bitRate);

    VTSessionSetProperty(encodingSession,
                         kVTCompressionPropertyKey_AverageBitRate,
                         bitRateRef);

    CFRelease(bitRateRef);


    int bitRateLimit = bitRate / 8;

    CFNumberRef bitRateLimitRef = CFNumberCreate(kCFAllocatorDefault,
                                                 kCFNumberSInt32Type,
                                                 &bitRateLimit);

    VTSessionSetProperty(encodingSession,
                         kVTCompressionPropertyKey_DataRateLimits,
                         bitRateLimitRef);

    CFRelease(bitRateLimitRef);

但这两行，我不明白：

int bitRate = VTB_WIDTH * VTB_HEIGHT * 3 * 4 * 8;

int bitRateLimit = bitRate / 8;

使用它们的正确方法是什么？

希望有人能告诉我。

谢谢你的时间！

Answer 1

来自kvtcompressionpropertykey_dataratelimits的文件说：

每个硬限制由数据大小（以字节为单位）和a来描述持续时间以秒为单位......

因此，您需要使用2个参数（数据大小，以字节为单位，持续时间以秒为单位）设置此属性

int bitRate = VTB_WIDTH * VTB_HEIGHT * 3 * 4 * 8; 
int bitRateLimit = bitRate / 8; 

// that's say we set data in byte/second
CFNumberRef byteNum = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRateLimit);
int second = 1;
CFNumberRef secNum = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &second);

// add parameters into a array
const void* numbers[2] = {byteNum, secNum};
CFArrayRef dataRateLimits = CFArrayCreate(NULL, numbers, 2, &kCFTypeArrayCallBacks);

// then set property with array
status = VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_DataRateLimits, arrayValues);

如何调整Videotoolbox中的属性？

1 个答案: