I use VTCompressionSession and set the average bit rate by kVTCompressionPropertyKey_AverageBitRate and kVTCompressionPropertyKey_DataRateLimits. The code like this: VTCompressionSessionRef vtSession = session; if (vtSession == NULL) { vtSession = _encoderSession; } if (vtSession == nil) { return; } int tmp = bitrate; int bytesTmp = tmp * 0.15; int durationTmp = 1; CFNumberRef bitrateRef = CFNumberCreate(NULL, kCFNumberSInt32Type, &tmp); CFNumberRef bytes = CFNumberCreate(NULL, kCFNumberSInt32Type, &bytesTmp); CFNumberRef duration = CFNumberCreate(NULL, kCFNumberSInt32Type, &durationTmp); if ([self isSupportPropertyWithSession:vtSession key:kVTCompressionPropertyKey_AverageBitRate]) { [self setSessionPropertyWithSession:vtSession key:kVTCompressionPropertyKey_AverageBitRate value:bitrateRef]; }else { NSLog(@"Video Encoder: set average bitRate error"); } NSLog(@"Video Encoder: set bitrate bytes = %d, _bitrate = %d",bytesTmp, bitrate); CFMutableArrayRef limit = CFArrayCreateMutable(NULL, 2, &kCFTypeArrayCallBacks); CFArrayAppendValue(limit, bytes); CFArrayAppendValue(limit, duration); if([self isSupportPropertyWithSession:vtSession key:kVTCompressionPropertyKey_DataRateLimits]) { OSStatus ret = VTSessionSetProperty(vtSession, kVTCompressionPropertyKey_DataRateLimits, limit); if(ret != noErr){ NSError *error = [NSError errorWithDomain:NSOSStatusErrorDomain code:ret userInfo:nil]; NSLog(@"Video Encoder: set DataRateLimits failed with %s",error.description.UTF8String); } }else { NSLog(@"Video Encoder: set data rate limits error"); } CFRelease(bitrateRef); CFRelease(limit); CFRelease(bytes); CFRelease(duration); } This work fine on iOS16 and below. But on iOS17 the bitrate of the generate video file is much lower than the value I set. For exmaple, I set biterate 600k but on iOS17 the encoded video bitrate is lower than 150k. What went wrong?