YouTube – Acceder a la imagen de portada de un vídeo

Tenemos diferentes medidas:

Por defecto:

https://img.youtube.com/vi//default.jpg

For the high quality version:

https://img.youtube.com/vi//hqdefault.jpg

There is also a medium quality version:

https://img.youtube.com/vi//mqdefault.jpg

For the standard definition version:

https://img.youtube.com/vi//sddefault.jpg

For the maximum resolution version:
https://img.youtube.com/vi//maxresdefault.jpg