I would like to know how can I synchronized a wav and an external video??

@anna Welcome to the forum...!
Like this......... sync.zip
The Pd Extended version works well..... the Pd Vanilla version I cannot test as I don't have Gem working on my machine. But the only change I have made for Vanilla is to use the right outlet of [soundfiler] to get the sample rate of the audio file. In Pd Extended we used [soundfile_info]
If you need an explanation please ask.
David.