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neels has posted comments on this change. ( https://gerrit.osmocom.org/c/osmo-mgw/+/31214 )

Change subject: mgcp_sdp: add fmtp string to define HR GSM RTP format ......................................................................

Patch Set 10: Code-Review-1

(1 comment)

File include/osmocom/mgcp/mgcp_common.h:

https://gerrit.osmocom.org/c/osmo-mgw/+/31214/comment/1701ba1a_21068860 PS10, Line 71: enum mgcp_gsm_hr_fmt gsm_hr_format; struct mgcp_codec_param has a fundamental problem: it lives in struct mgcp_msg, i.e. there can *only be one* in an entire SDP message in the osmo_mgcp_client API. However, "a=fmtp:<pt-nr>" are scoped *per payload type nr*, i.e. there should be one for every codec, not only one per SDP message.

amr_octet_aligned has this problem, meaning that our MGCP client cannot offer two distinct payload types for AMR octet-aligned and AMR bandwidth-efficient. This recently bit me while working on codec resolution in osmo-msc and osmo-bsc. So far I have to decide for OA or not for *all* AMR codecs represented in our mgcp_client SDP.

Let's not proliferate this problem. This probably means we first need to fix this scoping problem before adding new fmtp -- because when you make room for per-pt fmtp, might as well move the OA flag there.

(If you instead would want one global flag, it would be a new X-Osmo header; but I think per pt fmtp is the right choice here)