Modifying scrcpy to Force H264 Baseline Profile for Real-Time Android Screen Casting

Background: The cloud device platform currently uses two real‑time casting tools—STF's minicap, which captures screenshots, and scrcpy, which streams video but only supports Android 5.0+. Both have drawbacks; minicap lags behind new Android releases, while scrcpy cannot handle devices (e.g., Vivo, Oppo, Xiaomi 9) that output H264 streams with a High profile, which the Broadway web player only supports for baseline profiles.

Solution: Using a Xiaomi 9 (Android 9.0) as an example, the H264 stream was inspected and found to have profile_idc = 100 (High). By examining scrcpy’s source, the private createFormat method in ScreenEncoder was identified as the place to set the video format. The method was modified to force the profile to baseline ( profile_idc = 66 ).

Implementation steps:

Recompile the modified scrcpy source into a JAR file and push it to the device.

Execute on the device: CLASSPATH=/data/local/tmp/scrcpy-server.jar app_process / --nice-name=scrcpy_server com.genymobile.scrcpy.Server 0 8000000 true weight:height:0:0 false Note: each run clears the previously pushed JAR, so the JAR must be pushed before every start.

Run adb forward to forward the device’s socket to the PC and capture the video stream.

Parse the received H264 stream into individual frames and send them to the web front‑end, where the Broadway plugin plays the baseline H264 video, achieving real‑time casting.

Result: After the modification, the scrcpy‑generated video stream shows profile_idc = 66 , confirming the baseline format and successful playback in the web client.

Effect demonstration: Screenshots and GIFs illustrate the real‑time casting working correctly with the modified scrcpy.