Add an option to ignore PostProcessingError (was: --embed-thumbnail should warn, not error, on non-mp3/mp4)

[FGasper]

• [ x ] I've verified and I assure that I'm running youtube-dl 2016.04.19
• [ x ] At least skimmed through README and most notably FAQ and BUGS sections
• [ x ] Searched the bugtracker for similar issues including closed ones
• [ x ] Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• Feature request (request for a new functionality)
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> youtube-dl -x --embed-thumbnail http://youtube.com/watch?v=Jj1KTPOqd_A
[youtube] Jj1KTPOqd_A: Downloading webpage
[youtube] Jj1KTPOqd_A: Downloading video info webpage
[youtube] Jj1KTPOqd_A: Extracting video information
[youtube] Jj1KTPOqd_A: Downloading thumbnail ...
[youtube] Jj1KTPOqd_A: Writing thumbnail to: 01-Kenny Wayne Shepherd Band - Deja Voodoo (Video)-Jj1KTPOqd_A.jpg
[download] Destination: 01-Kenny Wayne Shepherd Band - Deja Voodoo (Video)-Jj1KTPOqd_A.webm
[download] 100% of 4.31MiB in 01:11
[ffmpeg] Destination: 01-Kenny Wayne Shepherd Band - Deja Voodoo (Video)-Jj1KTPOqd_A.ogg
Deleting original file 01-Kenny Wayne Shepherd Band - Deja Voodoo (Video)-Jj1KTPOqd_A.webm (pass -k to keep)
ERROR: Only mp3 and m4a/mp4 are supported for thumbnail embedding for now.

A failure to embed a thumbnail should probably be treated as a nonfatal error, don’t you think?

[Hrxn]

Well, not necessarily..

Works as expected, I'd say.
You have to specify a specific format that supports embedding, e.g:
youtube-dl -f 'bestvideo[ext=mp4]+bestaudio[ext=m4a]/best[ext=mp4]/best'

[FGasper]

@Hrxn I would agree if I were asking for a specific format, but in my case I’m just wanting “best”, whichever that happens to be.

If I specify a format, won’t there be loss of quality from lossy compression? In the example you gave, if “best” were, say, WebM, there’d be a recompression, no?

At the end of the day, I want:

• if the format supports thumbnails, embed
• otherwise, don’t embed

[yan12125]

Currently all post-processing options, such as --extract-audio, --embed-subs, halt youtube-dl in case of errors. It's a good idea to tolerate these errors, but we need a new option but not changing the semantic of existing options.

[FGasper]

It’s especially annoying for playlist downloads since you might get a failure at track 5 of a 25-track playlist.

[yan12125]

FYI: for playlists, --ignore-errors is handy.

[Hrxn]

If I specify a format, won’t there be loss of quality from lossy compression? In the example you gave, if “best” were, say, WebM, there’d be a recompression, no?

Well, depends on the source/site, technically.

But usually not. YouTube for example has a quite large selection of available formats, .webm being one of them, and there is nothing transcoded.

[yan12125]

Never. There's no recompression unless --recode-video is used. The container may be changed in merging, but the streams are simply copied.

[Hrxn]

Maybe some sites re-encode on the fly, depending on the request. Could be, you can't tell for sure on the client side.

Not that I've ever heard of such an example, but still...

[yan12125]

I assume @FGasper is talking about what happens in youtube-dl. Of course servers can do anything and we can't know.

[FGasper]

@Hrxn It’s not the transcoding that concerns me; it’s that youtube-dl would fetch a less-than-optimal format for the sake of embedding that thumbnail.

My own use case is that I always want the highest-quality audio. Then, add the thumbnail if that format allows.