Video related primitives should be provided in scraperlist

We are publishing more and more ZIM files with videos using many different scrapers.

Do do that we mainly:

• Re-encode videos/audio streams
• Handle sub-titles
• Display all of this using video.js

For the moment many of these pieces of video related functions are distributed in different places (in the scraper relying on them).

At least to me, this is:

• difficult to understand which scraper is at which status related to the development of these pieces of code
• Fixes will have to be requested/tracked in each scraper
• Releases are also de-facto made at very different times

I'm not prescriptive about the exact solution, but I believe we should try to consolidate this at one place.

Comienza por inventariar la funcionalidad relacionada con el vídeo que actualmente está distribuida entre los scrapers que utilizan python-scraperlib, incluida la recodificación de vídeo/audio, los subtítulos y la visualización con video.js. Define un único enfoque de consolidación e identifica qué consumiría cada scraper de él. Se considera terminado cuando estas primitivas se mantienen y publican desde un único lugar compartido.