Re: [Hls-interest] Setting appropriate cache levels for blocking parts and playlists on reference stream

[Jan Van Doorn <[e-mail]>]

> On Feb 25, 2021, at 9:30 AM, Law, Will <wilaw=[e-mail]> wrote:
> 
> Hartelijk bedankt!

Graag gedaan!
 
> I see the blocked playlist responses now have a max-age of 24, however the blocked media segments, such as the one shown below, are still at 300?

You're right, I missed a spot ;-). I think I have it right now? 

> GET /cmaf/media2/lowLatencySeg.mp4?segment=filePart280896.4.mp4 HTTP/2
> Host: ll-hls-test.apple.com
> User-Agent: curl/7.64.1
> Accept: */*
>
* Connection state changed (MAX_CONCURRENT_STREAMS == 100)!
< HTTP/2 200
< access-control-allow-origin: *
< block-duration: 243.192089ms
< cache-control: max-age=24
< content-length: 251821
< content-type: video/mp4
< server: ATS/8.1.1
< date: Thu, 25 Feb 2021 16:49:18 GMT
< access-control-expose-headers: age
< age: 0
< via: http/1.1 ussea4-edge-tx-004.ts.apple.com (ApacheTrafficServer/8.1.1 [uScMsSfWpSeN:t cCMp sS])
< cdnuuid: 301e6547-bc22-4e1c-b534-0198e21bc471-420944344
< x-cache: miss
< ms-in-cache: 0
<

>  
> Request URL: https://ll-hls-test.apple.com/cmaf/media1/lowLatencySeg.mp4?segment=filePart280487.3.mp4 <https://ll-hls-test.apple.com/cmaf/media1/lowLatencySeg.mp4?segment=filePart280487.3.mp4>
> Request Method: GET
> Status Code: 200
> Remote Address: 17.253.30.233:443
> Referrer Policy: strict-origin-when-cross-origin
> access-control-allow-origin: *
> access-control-expose-headers: age
> age: 1
> block-duration: 837.994439ms
> cache-control: max-age=300
> cdnuuid: b2341c67-2b51-4783-99f8-19e417e2c786-421560565
> content-length: 67099
> content-type: video/mp4
> date: Thu, 25 Feb 2021 16:23:01 GMT
> ms-in-cache: 0
> server: ATS/8.1.1
> via: http/1.1 ussea4-edge-tx-002.ts.apple.com <http://ussea4-edge-tx-002.ts.apple.com/> (ApacheTrafficServer/8.1.1 [uScMsSfWpSeN:t cCMp sS])
> x-cache: miss
>  
> Cheers
> Will
>  
>  
> From: Jan Van Doorn <jvd=[e-mail]>
> Date: Thursday, February 25, 2021 at 7:53 AM
> To: "Law, Will" <[e-mail]>
> Cc: "[e-mail]" <[e-mail]>
> Subject: Re: [Hls-interest] Setting appropriate cache levels for blocking parts and playlists on reference stream
>  
> Hi Will,
>  
> I updated the cmaf reference stream to have targetduration*6 as max-age. The ll-hls-origin-example.go will be updated accordingly in the next release of the Low Latency HLS Tools package.
>  
> Cheers,
> JvD
>  
> 
> 
>> On Feb 12, 2021, at 9:52 AM, Law, Will <wilaw=[e-mail] <mailto:wilaw=[e-mail]>> wrote:
>>  
>> A given LL-HLS stream consists of a sequence of playlists, parts and segments. The parts are only referenced within 3 target-durations from the live edge and hence can have a relatively short cache TTL , say 6 target durations to be safe . Segments however maybe requested by any client scrubbing within the DVR window, as well as further behind live by non-low-latency clients. These segments need a much longer TTL, at least the length of the DVR window, or longer if the live stream is converted to a VOD asset . Maximum cache efficiency is achieved when the proxy edge is able to evict objects as soon as their useful life has ended.
>>  
>> The current IETF spec addresses this with “Successful responses to blocking Media segment requests should be cached for six Target Durations.”,  “Successful responses to blocking Playlist requests should be cached for six Target Durations.” and “Origin servers should use Cache-Control headers to communicate the desired cache lifetime.”
>>  
>> Observing the Apple reference stream at https://ll-hls-test.apple.com/cmaf/master.m3u8 <https://ll-hls-test.apple.com/cmaf/master.m3u8>, with a target duration of 4. I note for successful responses that :
>>  
>> Non-blocking media playlist response: max-age = 1
>> Blocking media playlist response: max-age = 60
>> Blocking part response: max-age = 300
>> Non-blocking part response: max-age = 300
>> Non-blocking segment response: max-age = 300
>>  
>> Would it be more correct to have blocking media object (part) responses have a max-age of 24?
>>  
>> Should blocking media playlist responses also be reduced to  24?
>>  
>> Cheers
>> Will
>>  
>> -- 
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