Re: [Sframe] Partial decodability and IDUs

[Sergio Garcia Murillo <[e-mail]>]

You are right regarding that the SFrame layer does not need to know what 
is feed in for encryption, but in order to be able to have a working end 
to end solution for webrtc, someone will need to define what and how 
this IDUs are generated and reassembled for each codec if we want to 
have interoperable implementations in different devices.

That process is codec-dependant and I would require quite a lot of 
effort (and also supporting it on the agnostic packetization), so I 
would prefer to have strong arguments in favor of doing it.



On 19/11/2020 22:53, Justin Uberti wrote:
> The encoder needs to be aware of any mechanism to generate IDUs (e.g., 
> slices), and typically each of these IDUs will be handed up to the 
> consumer individually. So the SFRAME layer doesn't need to do any 
> splitting, it just knows that it should treat each IDU as something it 
> needs to individually SFRAME and packetize.
>
> On Thu, Nov 19, 2020 at 1:40 PM Sergio Garcia Murillo 
> <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     Hi all,
>
>
>     As most of you already know, this morning I made a presentation in
>     AVTCORE introducing the topic about the need to specify an
>     agnostic video codec packetization format.
>
>     https://datatracker.ietf.org/meeting/109/materials/slides-109-avtcore-sframe-rtp-encapsulation-00
>     <https://datatracker.ietf.org/meeting/109/materials/slides-109-avtcore-sframe-rtp-encapsulation-00>
>
>
>     I got an AP for creating an initial draft so it could be reviewed
>     and accepted.
>
>     However, there were two main concerns that we should address in
>     this this group:
>
>       * Historically, avtcore has explicitly designed not to be
>         payload agnostic and  declined to standardized codec agnostic
>         payload formats in  number of cases.  If that is to be
>         changed, needs to be done deliberately.
>       * Need to define the "minimum decoding unit" or "independently
>         decodable unit", that SFrame will work with.
>
>
>     Regarding the second one
>
>       * Full video frames (just use whatever is the encoder output)
>       * Spatial layer frames
>       * "independend decodable subframes" like h264 slices, vp8
>         partitions or av1 tiles which allows partial decodability
>         which is mainly aimed for enhancing packet loss resilience.
>
>
>     Spatial layer frames is the minimum we should target as if not it
>     will just prevent SFUs for using SVC codecs. So the question is if
>     we should go deeper and implement lower partitions of the frames
>     or not.
>
>
>     AFAIK, currently, libwertc does not support partial decodability
>     and I personally haven't seen any practical usage of this in the
>     RTC world (while it makes a lot of sense in streaming/broadcasting
>     world), but would like to hear what is the view and experience of
>     the other members of this group. Also note that if we are going to
>     support them on SFrame this will require a greater effort because
>     we will need to explicitly define how the frames must be split
>     before being encrypted y SFrame for *each* possible video codec
>     (h264,h265,vp8,vp9,av1,...).
>
>
>     There was also the question about how/if we should support other
>     codec features like DON/interleaved mode for h264, which I also
>     think we should not support mainly because we are not currently
>     using it on webrtc implementations.
>
>
>     What do you think?
>
>
>     Best regards
>
>     Sergio
>
>
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