在iOS上使用HEVC编码器输出视频大小
问题描述:
我有一个项目目前使用H.264编码器在iOS上录制视频。我想尝试在iOS 11中使用新的HEVC编码器来减小文件大小,但是发现使用HEVC编码器会导致文件大小膨胀。 Here's a project on GitHub that shows the issue - it simultaneously writes frames from the camera to files using the H.264 and H.265 (HEVC) encoders, and the resulting file sizes are printed to the console.在iOS上使用HEVC编码器输出视频大小
的AVFoundation类是设置这样的:
class VideoWriter {
var avAssetWriterInput: AVAssetWriterInput
var avAssetWriter: AVassetWriter
init() {
if #available(iOS 11.0, *) {
avAssetWriterInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: [AVVideoCodecKey:AVVideoCodecType.hevc, AVVideoHeightKey:720, AVVideoWidthKey:1280])
}
avAssetWriterInput.expectsMediaDataInRealTime = true
do {
let url = directory.appendingPathComponent(UUID.init().uuidString.appending(".hevc"))
avAssetWriter = try AVAssetWriter(url: url, fileType: AVFileType.mp4)
avAssetWriter.add(avAssetWriterInput)
avAssetWriter.movieFragmentInterval = kCMTimeInvalid
} catch {
fatalError("Could not initialize AVAssetWriter \(error)")
}
}
...
然后帧这样写的:
func write(sampleBuffer buffer: CMSampleBuffer) {
if avAssetWriter.status == AVAssetWriterStatus.unknown {
avAssetWriter.startWriting()
avAssetWriter.startSession(atSourceTime: CMSampleBufferGetPresentationTimeStamp(buffer))
}
if avAssetWriterInput.isReadyForMoreMediaData {
avAssetWriterInput.append(buffer)
}
}
,因为他们进来的AVCaptureVideoDataOutputSampleBufferDelegate
。在我录制的品质(720p或1080p)中,HEVC编码视频的文件大小应该是相同的H.264编码视频的40-60%,而我在使用默认相机应用时会看到这一点iOS,但是当我使用AVAssetWriter(或上面链接的项目)时,我看到HEVC的文件大小比使用H.264时的大三倍。要么我做错了什么,或者HEVC编码器工作不正常。我是否错过了一些东西,或者有什么解决方法让HEVC通过AVFoundation工作?
答
您是否尝试过指定比特率等? 如下:
NSUInteger bitrate = 50 * 1024 * 1024; // 50 Mbps
NSUInteger keyFrameInterval = 30;
NSString *videoProfile = AVVideoProfileLevelH264HighAutoLevel;
NSString *codec = AVVideoCodecH264;
if (@available(iOS 11, *)) {
videoProfile = (NSString *)kVTProfileLevel_HEVC_Main_AutoLevel;
codec = AVVideoCodecTypeHEVC;
}
NSDictionary *codecSettings = @{AVVideoAverageBitRateKey: @(bitrate),
AVVideoMaxKeyFrameIntervalKey: @(keyFrameInterval),
AVVideoProfileLevelKey: videoProfile};
NSDictionary *videoSettings = @{AVVideoCodecKey: codec,
AVVideoCompressionPropertiesKey: codecSettings,
AVVideoWidthKey: @((NSInteger)resolution.width),
AVVideoHeightKey: @((NSInteger)resolution.height)};
AVAssetWriterInput *videoWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
...
据我了解,用相同的比特率,文件大小应为H264和HEVC相同,但HEVC的质量应该更好。
我收到了类似的回应苹果。显然,H.264的默认比特率是5mbit,HEVC是30mbit。如果我尝试了这一点,它会起作用,我会报告并接受你的答案! – jpetrichsr