Technique to identify a video in iOS camera roll

I'm trying to solve a specific problem (but this could benefit others) which from googling around doesn't seem to have a definitive solution. I think there are probably several partial solutions out there, I'd like to find the best of those (or a combination) that does the trick most of the time.

My specific example is: users in my app can send videos to each other and I'm going to allow them to save videos they have received to their camera roll. I would like to prevent them from forwarding the video on to others. I don't need to identify a particular video, just that it was originally saved from my app.

I have achieved a pretty good solution for images by saving some EXIF metadata that I can use to identify that the image was saved from my app and reject any attempts to forward it on, but the same solution doesn't work for videos.

I'm open to any ideas. So far I've seen suggested:

1. Us开发者_Python百科ing ALAssetRepresentation in some way to save a filename and then compare it when reading in, but I've read that upgrading iOS wipes these names out

2. x-Saving metadata. Not possible.

3. MD5. I suspect iOS would modify the video in some way on saving which would invalidate this.

4. I've had a thought about appending a frame or two to the start of the video, perhaps an image which is a solid block of colour, magenta for example. Then when reading in, get the first frame, do some kind of processing to identify this. Is this practical or even possible?

What are your thoughts on these, and/or can you suggest anything better?

Thanks!

Steven

There are 2 approaches you could try. Both solutions only work under iOS5.

1) Save the url returned by [ALAssetRepresentation url]. Under iOS 5 this URL contains a CoreData objectID and should be persistent.

2) Use the customMetadata property of ALAsset to append custom info to any asset you saved yourself.

Cheers,

Hendrik