If the police search your house with a warrant can you film them to ensure they keep to the letter of the warrant?
The right to film police carrying out their duties is constitutionally protected. See, e.g, ACLU v. Alvarez, 679 F.3d 583 (7th Cir. 2012) and Glik v. Cunniffe, 655 F.3d 78 (1st Cir. 2011).
Of course, one could always imagine some fact pattern in which some other consideration overrode this constitutional right (e.g. filming would have had the effect of destroying evidence that was light sensitive, so the police were using night vision equipment).
Related: Boulder, Colorado pays $95,000 to settle the claim of a man arrested for filming the police.
You can film anyone in public or with the permission of the occupier of private premises (voyeurism excepted).
No* (in private premises) | Yes (in public spaces)
Police doesn't get a special protection from image rights than everyone else, except if the person is a member of a special force with anonymity protection (e.g. RAID, counter-terrorism or intelligence).
Which means that, according to Penal Code's 226-1, it's reprehensible
2° En fixant, enregistrant ou transmettant, sans le consentement de celle-ci, l'image d'une personne se trouvant dans un lieu privé.
2° By fixing, recording or transmitting, without the consent of the person, the image of a person in a private place.
But consent can be implicit if :
Lorsque les actes mentionnés aux 1° et 2° du présent article ont été accomplis au vu et au su des intéressés sans qu'ils s'y soient opposés, alors qu'ils étaient en mesure de le faire, le consentement de ceux-ci est présumé.
When the acts mentioned in 1° and 2° of this article have been performed in full view of the persons concerned without their having objected, even though they were able to do so, their consent is presumed.