Do not tell me to use AVAssetExportSession, thank you.
I tried this, but failed.
for (int i =0; i < count; i++) {
assetWriterInput = nil;
assetWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
NSParameterAssert(assetWriterInput);
NSParameterAssert([assetWriter canAddInput:assetWriterInput]);
[assetWriterInput setExpectsMediaDataInRealTime:YES];
[assetWriter addInput:assetWriterInput];
}
[assetWriter startWriting];