> I would think it would make more sense to just strip out the audio, rather than instruct browsers to ignore any audio tracks.
On the server's side, yes, that would make more sense. However, the fact is that the MP4 format supports audio, and it will always be possible for a server to supply a webpage with a GIFV item that points to an MP4 file that contains audio. What should the browser do in that case? Playing the audio is probably not desired. Refusing to display the video, or displaying "Warning: this video file contains audio and isn't a valid GIFV file", would probably just confuse or irritate the user--it's probably not their responsibility to fix the server's website. The remaining option seems to be that the browser ignores the audio track, and I'd say this is the necessary conclusion.
(Cf. how browsers deal with HTML that's missing a bunch of end tags.)
On the server's side, yes, that would make more sense. However, the fact is that the MP4 format supports audio, and it will always be possible for a server to supply a webpage with a GIFV item that points to an MP4 file that contains audio. What should the browser do in that case? Playing the audio is probably not desired. Refusing to display the video, or displaying "Warning: this video file contains audio and isn't a valid GIFV file", would probably just confuse or irritate the user--it's probably not their responsibility to fix the server's website. The remaining option seems to be that the browser ignores the audio track, and I'd say this is the necessary conclusion.
(Cf. how browsers deal with HTML that's missing a bunch of end tags.)