[Bug 20760] <video> Expose statistics for tracking playback quality

https://www.w3.org/Bugs/Public/show_bug.cgi?id=20760

Simon Waller <simon.waller@samsung.com> changed:

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--- Comment #2 from Simon Waller <simon.waller@samsung.com> ---
These metrics look like they have been designed to report on a software
decoder. Most embedded devices (TVs, STBs) use a hardware based decoder which
will be able to decode every frame it is asked to. It may be difficult for some
implementations to know how many frames have been decoded since that is being
done in this low level hardware and the appropriate hooks to get the
information probably don't exist.

For hardware decoders, the jitter is not measurable but would anyway be zero
(or near enough not to be a valid quality metric).

Another point to bear in mind is that the frame rate is not always constant. In
the UK, the HD broadcasts on DTT dynamically switch between 50i and 25p (this
is a valid thing to do and is within the video coding specifications - AVC in
this case).

When using hardware decoders, the quality of the video is not determined by the
speed of the decoder (which is always fast enough for the video codec profile
being used) but the bandwidth on the IP connections, ie it is determined by the
quality of the video encoding at the maximum bitrate that the IP connection can
support.

BTW: Since this is my first post, a few words of introduction. My background is
in STB and digital TV development but I now mainly cover standardisation
activities such as DVB, OIPF and HbbTV. I will be joining the joint conf call
tomorrow.

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Received on Monday, 18 March 2013 10:48:16 UTC