On 3/10/15 7:09 AM, Randell Jesup wrote:
On 3/10/2015 9:25 AM, [email protected] wrote:
Hi Byron,
I add "a=fmtp:97 level-asymmetry-allowed=1" in the answer sdp, and
then it works.
But actually, I don't think "fmtp" is a necessary attribute in sdp,
right?
Why FF37 does force other devices sending "fmtp" in answer?
a=fmtp is not generally *required* - however, for H.264, while there's
a default for packetization-mode (0), you should not assume a default
for profile-level-id or fail to provide it, even though in theory you
can (the default is 420010, which only allows a max resolution of
176x144@15fps).
It is an exceedingly minor bug that our code apparently requires an
ftmp line for H.264. No reasonable H.264 device should fail to
provide it.
If level-asymmetry-allowed is not specified, we must assume the
value is 0, and if profile-level-id is not specified, we must assume
420010 as jesup points out. Since these parameters are specified
independently by each end, if we offer something other than 420010, this
is a mismatch according to the spec. You can argue for bending/breaking
the spec in this case perhaps (where the missing fmtp comes in the
answer, and the offerer already specified that it supports
level-asymmetry, on the assumption that the answerer must have been ok
with level asymmetry also because otherwise it would have not used the
codec).
The reason for the behavior change is that we have completely
rewritten our JSEP engine, and one of the things the old one did was
break spec and assume a missing level-asymmetry-allowed param had a
default value of 1, instead of 0.
Best regards,
Byron Campen
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