Checking if a given frame is a key frame.

.mm

static BOOL isKeyFrame(CMSampleBufferRef sample)
{
    auto a = CMSampleBufferGetSampleAttachmentsArray(sample, 0);
    if (CFArrayGetCount(a) > 0) {
        CFBooleanRef value;
        auto b = CFDictionaryGetValueIfPresent
        ((CFDictionaryRef) CFArrayGetValueAtIndex(a, 0)
         , kCMSampleAttachmentKey_NotSync
         , reinterpret_cast<const void **>(&value))
        ;
        return !b || !CFBooleanGetValue(value);
    }
    return false;
}

ObjC:

static BOOL isKeyFrame(CMSampleBufferRef sample)
{
CFArrayRef a = CMSampleBufferGetSampleAttachmentsArray(sample, 0);
if (a && CFArrayGetCount(a) > 0) {
CFBooleanRef value;
Boolean b = CFDictionaryGetValueIfPresent((CFDictionaryRef) CFArrayGetValueAtIndex(a, 0), kCMSampleAttachmentKey_NotSync, (const void **)(&value));

    return !b || !CFBooleanGetValue(value);
}
return false;

}