I have read this post and this article. I believe I have done everything suggested: added the pipe to a module which is shared.
However, no matter what I do I cannot get my template to find the pipe I created. My app already has a Shared Module which the other modules import, so I create the pipe and added it to the shared module:
I created it with ng g pipe /shared/pipes/safe --flat --module shared --spec=false 
In SharedModule, I also added it to declarations and providers.
Everything runs, but it I try to use the pipe, as in:
<iframe width="600" height="360" [src]="video.acf.youtube_url | safe: 'url'" frameborder="0" allowfullscreen></iframe>
I just get an error
Error: Uncaught (in promise): Error: Template parse errors: The pipe 'safe' could not be found
The pipe itself is
import { Pipe, PipeTransform } from '@angular/core';
import { DomSanitizer, SafeHtml, SafeStyle, SafeScript, SafeUrl, SafeResourceUrl } from '@angular/platform-browser';
@Pipe({
  name: 'safe'
})
export class SafePipe implements PipeTransform {
  constructor(protected sanitizer: DomSanitizer) { }
  public transform(value: any, type: string): SafeHtml | SafeStyle | SafeScript | SafeUrl | SafeResourceUrl {
    switch (type) {
      case 'html': return this.sanitizer.bypassSecurityTrustHtml(value);
      case 'style': return this.sanitizer.bypassSecurityTrustStyle(value);
      case 'script': return this.sanitizer.bypassSecurityTrustScript(value);
      case 'url': return this.sanitizer.bypassSecurityTrustUrl(value);
      case 'resourceUrl': return this.sanitizer.bypassSecurityTrustResourceUrl(value);
      default: throw new Error(`Invalid safe type specified: ${type}`);
    }
  }
}
 
    