AVPlayerItem fails with AVStatusFailed and error code "Cannot Decode"

Question

I'm running into a strange issue, I hope someone can help.

In my iOS app I create a video with a custom soundtrack using MutableComposition by combining a video from the user's photo library and an audio file from the app bundle. I then use an AVPlayer and AVPlayerItem to play the video back to the user using a custom video player I made.

Each time a new composition is created, the assets, the player and the composition are cleared, released and it basically starts from a clean, init state.

All works fine, until after exactly 4 successful videos created this way every other attempt to create the player fails with error Cannot Decode. It does not matter if its the same video I'm recreating, has no relation to the size/length of the video or the audio file it simply always fails exactly on the fifth attempt, like clockwork. Once it fails, it will then always fail!

This is weird, because it just decoded the same video four times with no problem, so all of a sudden it fails? So, if anyone has a clue, please let me know.

Answer 1

Ok everyone, I have the answer to this straight from Apple. I used one of my developer TSI lifelines to ask the question, and I'll summarize the response.

There is a limit on the number of concurrent video players that AVFoundation will allow. It is due to the limitations of iOS hardware. The limit for current devices is 4 players. If you create a 5th player, you will get the "cannot decode" error. It is not a limit on the number of instances of AVPlayer, or AVPlayerItem. Rather,it is the association of AVPlayerItem with an AVPlayer which creates a "render pipeline", and you are limited to 4 of these. For example, this causes a new render pipeline:

AVPlayer *player = [AVPlayer playerWithPlayerItem:somePlayerItem];  
// assuming the AVPlayerItem is ready to go with an AVAsset that has been loaded

I was also warned that you cannot assume that you will have 4 pipelines available to you. Another App may be using one or more. Indeed, I have seen this happen on an iPad, but it was not clear which app was using a pipeline.

So, there you go, it was totally undocumented, but that is the story.