The social network has taken steps after the demand of streaming increased with large parts of Europe self-isolating at home due to the coronavirus pandemic.
While this change - which will apply to both the main Facebook platform and Instagram - means each video will use less data, viewers aren't likely to see a huge change in picture quality.
The company's decision comes after a number of streaming platforms introduced similar measures.
Amazon's Prime VIdeo, Netflix and Apple TV+ have all lowered their bitrates, but their range of resultions remains unaltered.
Meanwhile, the latter confirmed this meant its European users would use 25% less data while watching films.
For Disney+ users, the platform has revealed there would be slightly lower bitrates across Europe as the service launched in the UK, Ireland, Spain, Germany, Austria, Italy and Switzerland on Tuesday (24.03.20).
Its launch in France has been delayed until April 7 after a request from the country's government.