Hello tradeesse:

The English term “support” has two different grammatical functions: verb and noun and depending of the grammatical functions, we find different translations to Spanish. We can see this in the Collins English Spanish Dictionary.

In your case is “supporting” that is a verb in Present Participle. The verb “support” could be translating to Spanish as: sostener, apoyar, respaldar, confirmar…
Here, I am sharing with you the translations of Collins English Spanish Dictionary:
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Term: support: transitive verb
(= hold up) sostener ⇒ his knees wouldn't support him any more sus rodillas ya no lo sostenían ⇒ that chair won't support your weight esa silla no resistirá or aguantará tu peso ⇒ raise your upper body off the ground, supporting your weight on your arms apoyándose en los brazos levante el tronco del suelo ⇒ to support o.s. (physically) apoyarse (on en)
(= help)
(emotionally) apoyar
(financially)
[+ person] mantener
[+ organization, project] financiar
⇒ he has a wife and three children to support tiene una mujer y tres hijos que mantener ⇒ to support o.s. (financially) ganarse la vida
(= back)
[+ proposal, project, person] apoyar
⇒ his colleagues refused to support him sus colegas se negaron a apoyarlo
(sport)
[+ team] ⇒ who do you support? ¿de qué equipo eres (hincha)? ⇒ Tim supports Manchester United Tim es hincha de Manchester United ⇒ come and support your team! ¡ven a animar a tu equipo!
(= corroborate)
[+ theory, view] respaldar, confirmar
(= sustain) ⇒ an environment capable of supporting human life un medio en que existen las condiciones necesarias para que se desarrolle la vida humana ⇒ land so poor that it cannot support a small family un terreno tan poco fértil que no puede sustentar a una familia pequeña
(formal(= tolerate) tolerar
(music)
[+ band] actuar de telonero/teloneros de
⇒ a good band supported by an exciting new group un buen grupo con unos teloneros nuevos muy interesantes
(cinema, theatre)
[+ principal actor] secundar
⇒ he is supported by a wonderful cast está secundado por un estupendo reparto
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In your case, the translation is not “soporte” because “soporte” is a noun.

The concept associated with your case is: “respaldar”. Why? Because MPEG4 is a method of defining compression of audio and visual (AV) digital data. MPEG4 is a standard of the industry and YouTube supports this standard. (We say that MPEG4 is a standard is not really a theory but in the case of technology acts a a theory...)

Okay, we have the first easy translation of “YouTube supporting MPEG4” is “YouTube respalda el standard MPEG4”.

But when we talk of technology standards, we also use another word: “compatible”.

We say this device or this software or this program is “compatible”. or “non-compatible”. The translation of the English word “compatible” to Spanish is “compatible”. (different pronunciation but the same writing).

Here, we have the explanation of the Real Academia Española about “compatible”:
Term “compatible”: adj. Inform. Que puede funcionar directamente con otro dispositivo, aparato o programa. U. t. c. s. m.

And what is the quality to be compatible in Spanish: “compatibilidad” (In English: “compatibility”).
Here, the explanation of the Real Academia Española about “compatibilidad”
Term: “compatibilidad.” 1. f. Cualidad de compatible.
URL: http://lema.rae.es/drae/?val=compatible

In summary, we have different ways to translate “YouTube supporting MPEG4”
1) “… YouTube que respalda el formato MPEG4…”
2) “… YouTube que es compatible con el formato MPEG4…”
3) “… YouTube que brinda compatibilidad MPEG4…”

I hope this analysis helps you in your work.

Regards

Domingo
Note: Sources used in this analysis:
- Wikipedia about the explanation of MPEG4
- Microsoft Bilingual Glossary about the recommendation of a software company about the different uses of the terms “support” and “supporting”
- Collins English Spanish Dictionary about the different possible translation of “support”
- Dictionario de la Real Academia Española about the concepts: “compatible”, “compatibilidad”.