Creating a time range for AVAssetExportSession

问题:

I was wondering how to make a time range for AVAssetExportSession from time stamps such as:

NSTimeInterval start = [[NSDate date] timeIntervalSince1970];
NSTimeInterval end = [[NSDate date] timeIntervalSince1970];

The code that I am using for my export session is as follows:

AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality];

exportSession.outputURL = videoURL;
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
exportSession.timeRange = CMTimeRangeFromTimeToTime(start, end);

Thanks for your help!

回答1:

The property timeRange in AVAssetExportSession allows you to do a partial export of an asset specifying where to start and which duration. If not specified it'll export the whole video, in other words, it'll start at zero and will export the total duration.

Both start and duration should be expressed as CMTime.

For instance, if you want to export the first half of the asset:

CMTime half = CMTimeMultiplyByFloat64(exportSession.asset.duration, 0.5);
exportSession.timeRange = CMTimeRangeMake(kCMTimeZero, half);

or the second half:

exportSession.timeRange = CMTimeRangeMake(half, half);

or 10 seconds at the end:

CMTime _10 = CMTimeMakeWithSeconds(10, 600);
CMTime tMinus10 = CMTimeSubtract(exportSession.asset.duration, _10);
exportSession.timeRange = CMTimeRangeMake(tMinus10, _10);

Check CMTime reference for other ways to calculate the exact timing you need.