The module-full.sh config file includes --enable-decoder=adpcm_g726, however it also has --disable-decoders before it.
This results in the adpcm_g726le and adpcm_g726be decoders not being enabled, and ultimately my app not having sound when playing video.
I have fixed this on a local branch by specifying these two decoders in the module-full.sh file.
If you want I can open a PR for this.