publish to Twitter: if a photo size>5MB, shrink before posting

[tantek]

Just as Bridgy Publish automatically shortens (ellipses) text content when posting to Twitter, it would be nice if Bridgy Publish could also detect when a photo being posted was too big for Twitter and resize it to be just under 5MB* (and then link to the original post for the full resolution version).

*Twitter photos must be <=5MB according to this actual error from Bridgy Publish logs:

2016-12-02 01:43:34.244510 W Error 400, response body: {"errors":[{"code":..."message":"Image file size must be <= 5242880 bytes"}]}

Photo being attempted to publish:

https://indieweb.org/images/f/fc/2016-335-hwc-sf.gif

[snarfed]

interesting idea! thanks for filing. resizing automatically seems like a minor liberty, but probably fine as long as we clearly document when and how it happens.

sounds like there's also some uncertainty around how Twitter handles animated gifs in particular? i guess that's orthogonal though. never mind!

the actual resizing would be straightforward, using either PIL or app engine's API: https://cloud.google.com/appengine/docs/python/images/

[snarfed]

re animated gifs, looks like they have extra limits on frames, etc:

https://dev.twitter.com/rest/media/uploading-media.html#gifrecs

... but 5MB limit is the same:

https://dev.twitter.com/rest/media/uploading-media.html#imagerecs

except maybe the limit is actually 3MB, not 5MB? from the link above:

The filesize limit above is enforced by the media upload endpoint. In addition, there is a separate product entity specific filesize limit which is applied when calling the Tweet creation (or similar) endpoints with media_id. For example, it is possible to upload a 5 MB image, but the Tweet creation requires images to be <= 3 MB. The filesize limit and other constraints may vary depending on the media_category parameter.

unfortunate, and confusing. @tantek this is begging for some empirical testing! eg can you POSSE a 4MB photo? :P

[snarfed]

related via @tantek: PNG compression:

Zegnat: A lot of graphics tools let you do that pretty easy too. I think both Pixelmator and Acorn (image editors for macOS I have used / use) allow me to export as indexed PNGs. Can give huge size savings.
[tantek]: I definitely prefer things I don't have to install
[tantek]: Wonder if such PNG compression would be worth adding / requesting in Bridgy Publish
[tantek]: though maybe it's more worth doing it all up front so your "original" copy is also smaller / loads faster

[snarfed]

Obsolete, Bridgy Twitter is dead. #1410 (comment)