Posting video on instagram using hooks

Instagram's API doesn't directly support uploading anything from 3rd party applications. Therefore you have to do some ugly user experience compromises when providing the functionality to your users.

First, Prepare the video you want to upload to Instagram and store the path to it somewhere

Second, Save it to the user's Camera Roll:

if (UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(filePath)) {
    UISaveVideoAtPathToSavedPhotosAlbum(filePath, self, @selector(video:didFinishSavingWithError:contextInfo:), nil);
}

Third, now that the video is saved, tell the user that in order to upload the video to their Instagram, they must select it from their camera roll after clicking the upload button.

The upload button would simply do the following:

NSURL *instagramURL = [NSURL URLWithString:@"instagram://camera"];
if ([[UIApplication sharedApplication] canOpenURL:instagramURL]) {
    [[UIApplication sharedApplication] openURL:instagramURL];
}

It's very silly that the Instagram API doesn't support immediate media selection through any of the API endpoints for upload purposes, but as it stands right now, this is the only way.

I had a similar question: Instagram Video iPhone Hook and I figured it out. There is an undocumented iPhone hook that allows you to automatically select assets from the iPhones photo roll, and preload a caption for the video. This should give you the same user experience that Flipagrams app has with sharing a video to Instagram.

instagram://library?AssetPath=assets-library%3A%2F%2Fasset%2Fasset.mp4%3Fid%3D8864C466-A45C-4C48-B76F-E3C421711E9D%26ext%3Dmp4&InstagramCaption=Some%20Preloaded%20Caption

NSURL *videoFilePath = ...; // Your local path to the video
NSString *caption = @"Some Preloaded Caption";
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library writeVideoAtPathToSavedPhotosAlbum:[NSURL URLWithString:videoFilePath] completionBlock:^(NSURL *assetURL, NSError *error) {
    NSURL *instagramURL = [NSURL URLWithString:[NSString stringWithFormat:@"instagram://library?AssetPath=%@&InstagramCaption=%@",[assetURL absoluteString].percentEscape,caption.percentEscape]];
    if ([[UIApplication sharedApplication] canOpenURL:instagramURL]) {
        [[UIApplication sharedApplication] openURL:instagramURL];
    }
}];

try with:

instagram://library?AssetPath=yourVideoPath

i found the solution here: http://blog.horizon.camera/post/102273431070/video-share-objc-ios-instagram

Updated for iOS 9.

First, for iOS9 you'll need to add to your Info.plist file. Add a key a LSApplicationQueriesSchemes with the value instagram. This will whitelist the Instagram scheme. More info here.

Here is working code based on johnnyg17's:

NSString *moviePath = @"<# /path/to/movie #>";
NSString *caption = @"<# Your caption #>";
NSURL *movieURL = [NSURL fileURLWithPath:moviePath isDirectory:NO];
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library writeVideoAtPathToSavedPhotosAlbum:movieURL
                            completionBlock:^(NSURL *assetURL, NSError *error)
{
    NSURL *instagramURL = [NSURL URLWithString:
                           [NSString stringWithFormat:@"instagram://library?AssetPath=%@&InstagramCaption=%@",
                            [[assetURL absoluteString] stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet alphanumericCharacterSet]],
                            [caption stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet alphanumericCharacterSet]]]
                           ];
    if ([[UIApplication sharedApplication] canOpenURL:instagramURL]) {
        [[UIApplication sharedApplication] openURL:instagramURL];
    }
    else {
        NSLog(@"Can't open Instagram");
    }
}];

A sample instagramURL would be:

instagram://library?AssetPath=assets%2Dlibrary%3A%2F%2Fasset%2Fasset%2Emov%3Fid%3D69920271%2D2D44%2D4A84%2DA373%2D13602E8910B6%26ext%3Dmov&InstagramCaption=Super%20Selfie%20Dance%20%F0%9F%98%83

Update 2016/5: Note that ALAssetsLibrary is now deprecated for saving to users photo album, and the Photos Framework is now reccomended.