YouTube API: Get upload playlistID for YouTube Channel - youtube-api

Question

I'm trying to figure out the best way to get a channel's upload playlistID given the channel's channelID. E.g. for the channel with channelID
UC9CuvdOVfMPvKCiwdGKL3cQ
The corresponding upload playlistID is
UU9CuvdOVfMPvKCiwdGKL3cQ
Notice the second character has changed from a "C" to a "U"
I can do this transformation via string manipulation, but I'm curious if there's a better, less hacky way to find the upload playlist ID through the official youtube api.
Here's some Kotlin code that shows my issue:
I can find the ChannelID for the "Game Grumps" channel through the following youtube api v3 search:
val req = youtube.search().list("snippet");
req.key = {API_KEY}
req.q = "Game Grumps"
req.type = "channel"
val response = req.execute();
The resulting Channel id (response.items[0].snippet.channelId) is UC9CuvdOVfMPvKCiwdGKL3cQ
But when I run the following to try to get the videos uploaded by the channel, I have to use the transformed ChannelID (starting with UU instead of UC)
val req = youtube.PlaylistItems().list("snippet")
req.playlistId = "UU9CuvdOVfMPvKCiwdGKL3cQ"
req.key = {API_KEY}
val response = req .execute()
If I use the untransformed "UC" channelID, I get the following error: The playlist identified with the requests playlistId parameter cannot be found.
Instead of just replacing the second character with a "U", what's the more robust way (e.g. using the youtube API) of translating a ChannelID to a PlaylistID (for the uploads from that channel)?

Answer 1

I would suggest using the official Youtube API, instead of trying to manipulate the strings. You can follow the instructions here:
Instructions to get video ids for all uploaded videos for a channel in V3
Get the channel id for the channel you want (you probably only need to do this once, then you can save it)
Use search.list
Set type to channel
Set q to the name of the channel you want
Grab the channel id (something like this: "channelId": "UC0X2VuXXXXXXXXXXXXXXXX")
Get the playlist id for the channel uploads using the channel id from step 1 (you probably only need to do this once, then you can save it)
Use channels.list
Set id to UC0X2VuXXXXXXXXXXXXXXXX from step 1
Grab the uploads key from contentDetails (something like this: "uploads": "UU0XXXXXXXXXXXXXXXXXXXX")
Get the videos via the playlistitems in the playlist using the playlist id from step 2
Use playlistItems.list
Set playlistId to UU0XXXXXXXXXXXXXXXXXXXX from step 2
Go through each PlaylistItem and pull out the video id