[FFmpeg-user] G.726 codeword packing

[Arthur Grant]

I have a question about G.726 codeword packing.
I'm using the following command to convert 16bit, 8kHz, 1channel LPCM into
a G.726

ffmpeg -i 8k16bitpcm.wav -codec g726  out_g726.wav

The output file is with wFormatTag = 0x0045 (AV_CODEC_ID_ADPCM_G726)
The output G.726 is using AAL2 type codeword packing.
My question is why the output is using AAL2 type codeword packing?
The other type of codeword packing is as in RFC355. I checked the source
code libavcodec\g726.c and it looks like that the implementation always
uses the AAL2 type codeword packing.

Which standard or specification states that G.726 in WAVE should use AAL2
type codeword packing?

Thanks!
Arthur Grant