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Bonjour à tous, en ces temps de confinement scolaire, je dépose des capsules vidéo (mp4) sur dl.free.fr pour mes élèves mais lorsque je tente de les télécharger (afin de tester les liens), Firefox tente de les lire directement quand je clique sur valider et télécharger, puis les reconnait comme des fichiers audio.
Avec Chromium-stable (que j'ai installé pour cette occasion), le téléchargement de la vidéo débute sans soucis. Comment obtenir le même comportement de Firefox ?
Merci d'avance pour vos réponses.

The server sends this headers:
Content-Type: application/octet-stream
Content-disposition: filename=*.mp4

I believe that Firefox not should to play videos (it possibly a bug), but this is a moot point.

Solutions:

1. Use other formats instead of mp4 (mkv, ts, avi). The only problem is mp4.

2. (in about:config) set the value media.play-stand-alone=false (after that you will not be able to play mp4 and mp3 sent directly to the browser. It will offer to download)

(there are also media.mp4.enabled and media.webm.enabled parameters, but it is not recommended to change them, because it will break other sites, all online videos will stop playing everywhere)

3. Use Chromium

4. Add files to archive (zip, 7z)

URLs to check (ogg though, but it doesn't matter):
http://haignet.co.uk/html5-video-element-test.htm
http://haignet.co.uk/html5-video-element-test.ogg (direct link)

Google search keywords: "firefox play application/octet-stream mp4"

Offtopic:
To have YouTube offer H.264 (MP4) instead of VP9 (WebM), set this value:
media.mediasource.webm.enabled=false
(Or more brutally media.webm.enabled=false, but this will break webm online videos on all sites. Although there are usually fewer of them compared to mp4).
H.264 has a higher quality and loads the processor less.

mp4, webm, mkv, ts, avi, flv, ogm, mpg, vob - are containers (wrapper)
h264 (aka avc), h265 (aka hevc), vp8, vp9, av1, xvid, mpeg1, mpeg2 - are video codecs
mp2, mp3, aac, vorbis, opus, ac3 (aka dolby digital), dts - are audio codecs

In mp4, the index can be located either at the beginning of the file, or at the end of the file (most often). If it is located at the beginning, then mp4 is called "streaming friendly".

You can check it like this:
sudo urpmi mediainfo
mediainfo input.mp4 -full | grep Streamable

The point is that mp4 format has a limitation. If the index is located in the tail, and the file is not fully downloaded, then it is completely impossible to identify and play (the format will be considered unknown until the download is complete).
In the settings of mp4 muxer in Avidemux, you can change the way the index is stored.

"puis les reconnait comme des fichiers audio"
Most likely you are using MPEG4 ASP codec (aka XviD) in mp4 container. Firefox doesn't support MPEG4 ASP and only plays the audio track.

Édité par Visiteur Le 07/04/2021 à 07h20

Merci Artenox (même si je préfère en français...) la solution 2 est la bonne pour moi.

You are welcome.
Je craignais que les traducteurs en ligne ne puissent pas traduire correctement.