ios - 如何使用 AVAssetWriter 制作缩小尺寸的视频？

Question

我会制作缩小尺寸的视频，宽度可能为 50 像素，长度可能为 75 像素。这些是物理维度。

如何设置？在视频设置？我认为 AVVideoWidthKey 和 AVVideoHeightKey 更多的是为了分辨率而不是我需要的物理尺寸。

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt: 320], AVVideoWidthKey,    
                               [NSNumber numberWithInt:480], AVVideoHeightKey,   
                               nil];
AVAssetWriterInput* writerInput = [[AVAssetWriterInput
                                    assetWriterInputWithMediaType:AVMediaTypeVideo
                                    outputSettings:videoSettings] retain

Answer 1

您需要设置视频编解码器参数:

NSDictionary *videoCleanApertureSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                           [NSNumber numberWithInt:320], AVVideoCleanApertureWidthKey,
                                           [NSNumber numberWithInt:480], AVVideoCleanApertureHeightKey,
                                           [NSNumber numberWithInt:10], AVVideoCleanApertureHorizontalOffsetKey,
                                           [NSNumber numberWithInt:10], AVVideoCleanApertureVerticalOffsetKey,
                                            nil];


NSDictionary *videoAspectRatioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                             [NSNumber numberWithInt:3], AVVideoPixelAspectRatioHorizontalSpacingKey,
                                             [NSNumber numberWithInt:3],AVVideoPixelAspectRatioVerticalSpacingKey,
                                                    nil];



NSDictionary *codecSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               [NSNumber numberWithInt:960000], AVVideoAverageBitRateKey,
                               [NSNumber numberWithInt:1],AVVideoMaxKeyFrameIntervalKey,
                               videoCleanApertureSettings, AVVideoCleanApertureKey,
                               //videoAspectRatioSettings, AVVideoPixelAspectRatioKey,
                               //AVVideoProfileLevelH264Main30, AVVideoProfileLevelKey,
                               nil];





NSString *targetDevice = [[UIDevice currentDevice] model];

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               codecSettings,AVVideoCompressionPropertiesKey,
                               [NSNumber numberWithInt:320], AVVideoWidthKey,
                               [NSNumber numberWithInt:480], AVVideoHeightKey,
                               nil];