Is it possible to connect a USB soundcard to an Android phone, with an USB OTG cable?
... and then use this USB soundcards's stereo input as audio when making a video with the phone?
Yes it is possible. I'm doing this with several devices for amateur radio and video production with KineMaster Pro. For amateur radio, I use the DigiMaster MiniProSC connected via OTG cable to a Nexus 9 via OTG cable. I also do this with SignaLink usb connected the same way. Both of these devices have internal usb sound cards with audio in, audio out, and usb connection between android tablet and the radio.
For YouTube videos, I use KineMaster Pro with Zoom H2 and H4 as external microphone or line in. Both connected via USB to the Nexus 9, and both work perfectly!
I know this is an old thread, but when I saw the answer from the guy who says it doesn't work, I wanted to correct this out-of-date information, letting everyone who makes there way here via Google search of the correct answer!
Btw, it also works on Samsung galaxy s4 i9506. I've tested on Android 5, 6 and 7 successfully.
Yes, it is (mostly) possible.
Many (including some interfaces from RME, Focusrite, Behringer, M-Audio, ...) but not all audio interfaces are class compliant.
Many phones nowadays don't come with a headphone jack. Those USB adapters or USB headphones are in turn a small sound card.
I haven't tried it yet but extreamsd's USB Audio Recorder PRO seems to do what you want. There is a demo version.
No. Android doesn't support drivers for these types of devices. Its support for external devices is pretty limited to simple input devices, such as keyboards and mice, and storage devices, along with occasional special peripherals that your individual app would be designed to use. A PC sound card is way outside of its functionality.