Re: Encoders (Re: Getting rid of SDP) - Timestamps for media

On 16/03/2018 12:27, Cullen Jennings wrote:
>
>> On Mar 13, 2018, at 10:37 PM, Harald Alvestrand <harald@alvestrand.no 
>> <mailto:harald@alvestrand.no>> wrote:
>>
>>> * capture time of frame
>> are you thinking SMTPE timecodes (absolute capture time, possibly far 
>> in the past for recorded media) or RTP-clock-style "timestamp that 
>> can be used for relative positioning in time"?
>
> I have work with SMTPE  timecode a bunch for moving broadcast studios 
> to IP. It seems like a bad match for interactive media. Dropframe 
> handling alone should be enough to convince anyone. I realize 
> broadcast TV needs all that but we don't.
>
> I would prefer something that is a direct or indirect mapping to NTP 
> time with ms resolution.
>
> It might seem like something with no leap seconds, like GPS time, was 
> easier to use but I think the operating system end up providing such 
> good support for time with leap seconds that it ends up being easier.

IMHO what it would be needed is the ability to attach custom metadata to 
each encoded frame (it could be a timestamp, or an app-defined-data). It 
could be implemented as an rtp header extension and would trigger an 
"metadata" js event on the receiver side to this info is available to 
the app.

Best regards

Sergio