Re: [Hls-interest] Clarification on client and origin behavior with byte-range addressed LL-HLS

> On Sep 25, 2023, at 8:37 AM, Law, Will <wilaw=40akamai.com@dmarc.ietf.org> wrote:
> 
> Hello
>  
> I’m looking for some clarification on intended client and origin behavior when playing back LL-HLS with byte-range addressing.
>  
> # This is Playlist update 3
> #EXTINF:4.08,
> fs270.mp4
> #EXT-X-PART:DURATION=1.02,URI="fs271.mp4",BYTERANGE="20000@0",INDEPENDENT=YES
> #EXT-X-PART:DURATION=1.02,URI="fs271.mp4",BYTERANGE="23000@20000"
> #EXT-X-PART:DURATION=1.02,URI="fs271.mp4",BYTERANGE="18000@43000",INDEPENDENT=YES
> #EXT-X-PART:DURATION=1.02,URI="fs271.mp4",BYTERANGE="19000@61000"
> #EXTINF:4.08,
> fs271.mp4
> #EXT-X-PART:DURATION=1.02,URI="fs272.mp4",BYTERANGE="21000@0",INDEPENDENT=YES
> #EXT-X-PRELOAD-HINT:TYPE=PART,URI="fs272.mp4",BYTERANGE-START=21000
>  
> Given the snippet above, how should the player load the hinted part? It knows it starts at an offset of 21000 but it does not know the end. Per the spechttps://datatracker.ietf.org/doc/html/draft-pantos-hls-rfc8216bis#section-4.4.5.3, if the last-byte-pos is unknown, then the player should use RFC8673 and a last-byte-pos value of 9007199254740991. Seeing an incoming range request of range: 21000-9007199254740991, what should the origin do? Does it
> Serve bytes from 21000 to the end of the part
> Serve bytes from 21000 to the end of the segment
> Do something else
>  
> If [a], that would be a departure from standard HTTP range request semantics. If [b], now the player receives all the remaining parts in that segment, instead of just the hinted part.

We (and the various Apple players) expect (b). 

Note as well that the spec (section 6.2.6) also says:

   When processing requests for a URI or a byte range of a URI that
   includes one or more Partial Segments that are not yet completely
   available to be sent - such as requests made in response to an EXT-X-
   PRELOAD-HINT tag - the server MUST refrain from transmitting any
   bytes belonging to a Partial Segment until all bytes of that Partial
   Segment can be transmitted at the full speed of the link to the
   client.  If the requested range includes more than one Partial
   Segment then the server MUST enforce this delivery guarantee for each
   Partial Segment in turn. 

which implies (b), I believe.

Roger.

>  
> Cheers
> Will
>  
>  
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