Question, Checking downloaded videos and fragments

[latot]

Hi all, i have a question about how youtube-dl works, in start for example, when we download a video, anywhere, if we try download it again just finish, because the file is already downloaded, so do nothing.

But how youtube-dl knows the file is right?, is checked?

The same when we download a video, but the video is downloaded in fragments, if we download it again will do nothing, but how can we know if the fragments are right?

I would like to know if youtube-dl have some method or way to check the integrity of the downloaded data.

I don't know this so maybe youtube-dl check the downloaded video with the already downloaded when we try download again, or if not, we will don't download the file again but we will keep the wrong file....

Ty

[dstftw]

It does not actually know. If a file with target name already exists youtube-dl assumes it was already downloaded.
In general you can't check the integrity cause this requires obtaining some sort of checksum as metadata prior to downloading. Very few services provide such metadata.

[latot]

u.u

Ty for your response.

Okis, a realted question, i notice when i try download with the option --all-formats youtube-dl was trying to download other links but don't download anything because all the filenames was the same, but i notice the url of all files was different, this happen in iqiyi, maybe the webpage is sotoring multiples formats but all with the same names with differents urls?

Bye!

[dstftw]

In case of downloading multiple formats of the same video you should provide output template that will guarantee unique filenames for different formats, e.g. by adding format_id.

[latot]

That will works even if is in cache?, i mean youtube-dl to know if a file is downloaded compare the filename provided by the url or the user?

[latot]

and iqiyi seems to be saving the files in the same format mp4, but one mp4 can be in good quality and others not.