VideoTexture on iOS - NetStream.Play.Failed

I'm trying to get a video to play in an Away3d texture on iOS. It's fine on Android and Windows.

The video will play in Starling on IOS so I know it's not the video.

Here is how I add the video

        sphereGeometry =newSphereGeometry(5000,64,48);
        panoTextureMaterial =newTextureMaterial(panoTexture2DBase,false,false,false);  
        panoVideoMesh =newMesh(sphereGeometry, panoTextureMaterial); panoVideoMesh.scaleX *=-1;  
        panoVideoMesh.rotate(Vector3D.Y_AXIS,-90);  
        scene.addChild(panoVideoMesh);
        panoTexture2DBase.player.play();
        view.render();

On iOS I get this from the netstats when I try and load it as a video texture.

NetStream.Play.Start
NetStream.Play.Failed
NetStream.Play.Stop

I'm using the Away3d NativeVideoTexture class

        texture = context.createVideoTexture();
texture.attachNetStream(_player.ns);

I think it might be do with MP4 encoding, and I've had a good look around and can't find anything that works,

currently I'm trying this in FFMEG

-vcodec libx264 -profile:v main -level 3.1-crf 23-s 1024:768-movflags +faststart  

But what I set doesn't seem to make a lot of difference.

Any idea why my video is failing to load as a VideoTexture on iOS?