[Live-devel] Confused about how to generate fmtp line for H.264 source for SDP

[Jeremy Noring]

On Wed, Aug 3, 2011 at 6:51 PM, Ross Finlayson <finlayson at live555.com>wrote:

> Yes, it's uncommon for a supplier of a H.264 stream to know the SPS and PPS
> NAL units, but for those NAL units not to appear in the stream.  Most
> commonly, these NAL units appear in the stream, but you don't know what they
> are - and can find them out only by scanning the stream.  We now do that for
> you.
>

I don't think this is actually that common--most encoders go out of their
way to provide this data for you, and to get things running quickly it can
be very important to have SPS/PPS on hand.  Most container formats, such as
MP4, make this data readily available (you can put it in stream, but it's
bad form, IMO).


>
> Hmm, I'll look into it, but my encoder gives me the sps and pps when I
> initialize it, it seems like it would be easier to just hand the sps and pps
> to the rtp sink and just re-implement auxSDPLine in my class, pretty much
> like I used to do. Is there a reason your recommending this approach
>
>
> Yes, the reason was that it would probably save you work.  If the SPS and
> PPS NAL units also appear in the stream (which, for most encoders, they
> will), then you don't have to do any extra work (except perhaps duplicate
> some code that we already have in "H264VideoFileServerMediaSubsession").
>

FWIW, I ran into the same issue when I updated my Live555 version.  It's
hard to write an on-demand session because there's no clean way of handing
off the SPS/PPS info before things are up and running.
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