On 5/20/2015 12:53 PM, [email protected] wrote:
Thank you for prompt response. I've been told that it is mandatory to support
baseline profile? The other legacy devices must have chosen the lowest common
level due to interoperability concerns, so why does Firefox not do this?
Constrained Baseline < Baseline < Main < High (etc). More or less.
Most people didn't give a lot of thought to the SDP they generate
(especially years ago); they tended to copy existing uses/examples.
The rtcweb working group agreed on Constrained Baseline as the
requirement for rtcweb/WebRTC.
Admittedly I know nothing of codecs, but what does translating the
profile-level-id value entail (I'm assuming this is beyond simply manipulating
SDP)?
Just changing the SDP offer or response from the far-end device from
4280xx (or 4288xx) to 42E0xx/42E8xx - just SDP editing. In practice
they're normally interchangeable. From Wikipedia:
Baseline Profile:
Primarily for low-cost applications that require additional data
loss robustness, this profile is used in some videoconferencing and
mobile applications. This profile includes all features that are
supported in the Constrained Baseline Profile, plus three additional
features that can be used for loss robustness (or for other purposes
such as low-delay multi-point video stream compositing). The
importance of this profile has faded somewhat since the definition
of the Constrained Baseline Profile in 2009. All Constrained
Baseline Profile bitstreams are also considered to be Baseline
Profile bitstreams, as these two profiles share the same profile
identifier code value.
Note that the data loss robustness really doesn't come into play in
webrtc and interactive RTP traffic generally.
--
Randell Jesup, Mozilla
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