Avoid Video Compression when Selecting Movie with UIImagePickerController?

问题

I'm using UIImagePickerController to allow my user to select a video from the asset library.

When the user selects the "Choose" button on the second screen, the view displays a progress bar and a "Compressing Video..." message.

Why is this happening?

Is there some way I can avoid this compression operation?

回答1:

Answer: There is currently no way to control how UIImagePickerController compresses the picked video.

I just did some quick tests. Using a test app I created, I picked the same video two times -- once with the videoQuality property set to UIImagePickerControllerQualityTypeHigh and once with it set to UIImagePickerControllerQualityTypeLow. The resulting files that were copied over are exactly the same size, 15.1MB with a frame size of 360x480. The original was 72.5MB with a frame size of 480x640. Apparently this property doesn't affect the compression used at all.

回答2:

Set the videoQuality property of the UIImagePickerController to "High" (UIImagePickerControllerQualityTypeHigh = 0)

From the SDK documentation: "If displaying a recorded movie in the image picker, specifies that you do not want to reduce the video quality of the movie."

http://developer.apple.com/iphone/library/documentation/uikit/reference/UIImagePickerController_Class/UIImagePickerController/UIImagePickerController.html#//apple_ref/doc/c_ref/UIImagePickerControllerQualityType

回答3:

Since there is no way yet to avoid compression using UIImagePickerController, I wanted to include some ideas of how you can create your own image picker that will avoid compression.

This will allow access to the raw video files:

iOS 8

PHFetchResult *assetsFetchResult = [PHAsset fetchAssetsWithMediaType:PHAssetMediaTypeVideo options:nil];
for (PHAsset *asset in assetsFetchResult) {
    PHVideoRequestOptions *videoRequestOptions = [[PHVideoRequestOptions alloc] init];
    videoRequestOptions.version = PHVideoRequestOptionsVersionOriginal;

    [[PHImageManager defaultManager] requestAVAssetForVideo:asset options:videoRequestOptions resultHandler:^(AVAsset *asset, AVAudioMix *audioMix, NSDictionary *info) {
        // the AVAsset object represents the original video file
    }];
}

Look at the PhotoKit documentation for accessing collections (moments) and other options.

Here is a sample app from Apple using PhotoKit that could be modified to be a photo picker: https://developer.apple.com/library/ios/samplecode/UsingPhotosFramework/Introduction/Intro.html

Here is a photo picker library on GitHub that uses PhotoKit that looks promising since it gives you the PHAsset objects for all the selected images/videos: https://github.com/guillermomuntaner/GMImagePicker

iOS 7 and below

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];

[library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    if (group) {
        // If you want, you can filter just pictures or videos
        // I just need videos so I do this:
        [group setAssetsFilter:[ALAssetsFilter allVideos]];

        [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop){
            if (asset){
                // You can now add this ALAsset in your own video picker.
                // Note that you can only access the ALAsset as long as 
                // you maintain a reference to the ALAssetsLibrary

                // Or if you want to process the video, you can create an AVAsset:
                NSURL *url = asset.defaultRepresentation.url;
                AVAsset *videoAsset = [AVAsset assetWithURL:url];
            }
        }];
    }
} failureBlock:^(NSError *error) {
    NSLog(@"error enumerating AssetLibrary groups %@\n", error);
}];

回答4:

Starting from iOS 11, you can specify the videoExportPreset and set it to AVAssetExportPresetPassthrough:

picker.videoExportPreset = AVAssetExportPresetPassthrough

This will still show the "compressing" progress bar though, but will be much faster, especially for smaller videos.

回答5:

For those giving the advice to use the videoQuality property, documentation is clearly stating that it is a video capture option, not a picker option.

As Jack is mentioning it below, it is also for transcoding. Looks like I read the doc too quickly because I didn't notice the transcoding mention.

来源：https://stackoverflow.com/questions/3159061/avoid-video-compression-when-selecting-movie-with-uiimagepickercontroller