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Re: [Hls-interest] rendition report clarification

Eryk Vershen <evershen@apple.com> Mon, 29 March 2021 15:53 UTC

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From: Eryk Vershen <evershen@apple.com>
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Date: Mon, 29 Mar 2021 08:52:50 -0700
Cc: hls-interest@ietf.org
To: Scott Kellicker <scott@blankcanvas.video>
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Subject: Re: [Hls-interest] rendition report clarification
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> From: Scott Kellicker <scott@blankcanvas.video <mailto:scott@blankcanvas.video>>
> Date: March 26, 2021 at 8:48:44 AM PDT
> To: hls-interest@ietf.org <mailto:hls-interest@ietf.org>
> Subject: [Hls-interest] rendition report clarification
> 
> 
> At least to me the spec is not clear about rendition-reports between audio streams and video streams.  Looking at LLHLS streams produced by several companies, I see different behavior.
> 
> To take an example.  If I have one audio group rendition and 3 video renditions which point back to the audio group.  For example:
> 
> curl http://IP/playlist.m3u8 <http://ip/playlist.m3u8>
> #EXTM3U
> #EXT-X-VERSION:6
> #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="Audio",URI="audio1.m3u8"
> #EXT-X-STREAM-INF:BANDWIDTH=3600000,CODECS="avc1.4d4c28,mp4a.40.2",RESOLUTION=1920x1080,AUDIO="Audio"
> video1.m3u8
> #EXT-X-STREAM-INF:BANDWIDTH=1400000,CODECS="avc1.4d4c1e,mp4a.40.2",RESOLUTION=540x360,AUDIO="Audio"
> video2.m3u8
> #EXT-X-STREAM-INF:BANDWIDTH=750000,CODECS="avc1.4d4c15,mp4a.40.2",RESOLUTION=320x240,AUDIO="Audio"
> video3.m3u8
> 
> Q. When I return the m3u8 for one of the video renditions, should the REND-REPORT contain the audio m3u8?
> 
> $ curl http://IP/video1.m3u8 <http://ip/video1.m3u8> |grep REND. ; should have all the audio RRs when requesting video m3u8
> #EXT-X-RENDITION-REPORT:URI="audio1=.m3u8",LAST-MSN=131,LAST-PART=1
> #EXT-X-RENDITION-REPORT:URI="video2.m3u8",LAST-MSN=131,LAST-PART=1
> #EXT-X-RENDITION-REPORT:URI="video3.m3u8",LAST-MSN=131,LAST-PART=1

Yes.

See Appendix B.1 in draft-pantos-hls-rfc8216bis-07 (or later) -

   "Each Media Playlist contains one EXT-X-RENDITION-REPORT tag for each
    Media Playlist (Rendition) in the Master Playlist, except for the Media Playlist
    to which the EXT-X-RENDITION-REPORT tag is being added, and Playlists
    that contain the EXT-X-I-FRAMES-ONLY tag."


> Q. Conversely, when I return the rendition report for the audio rendition, should it contain the 3 video rend report entries?
> 
> curl http://IP/audio1.m3u8 <http://ip/audio1.m3u8> |grep REND.  ; should have all the video RRs when requesting audio m3u8
> #EXT-X-RENDITION-REPORT:URI="video1.m3u8",LAST-MSN=122,LAST-PART=1
> #EXT-X-RENDITION-REPORT:URI="video2.m3u8",LAST-MSN=122,LAST-PART=1
> #EXT-X-RENDITION-REPORT:URI="video3.m3u8",LAST-MSN=122,LAST-PART=1

Yes, for the same reason.


> mediastreamvalidator would seem to answer "yes" to both questions.  However, in my experience MSV is often wrong and can conflict with the spec.  (And what ultimately matters is the spec AND what players expect)

Please take the time to submit bugs against the mediastreamvalidator.

regards,
Eryk Vershen
Apple Inc

> 
> Scott Kellicker
> Blank Canvas Video LLC
> 
> 
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