On 30/04/18 13:56, Jim web wrote:
I've been discussing the 'loss' of the 1280x720 25fps version with someone
at the BBC.
IIUC this stemmed from 'Red Bee' days of yore, and until recently people at
the BBC had thought they had stopped it long ago. Someone apparently
noticed recently that it was still available. And then actually disabled
it. Hence the mysterious recent ending of its availablity.
I have made the point that the 1280x720 25fps version is useful for people
with a content 'cap' problem, etc, so will be missed because the 50fps
version means somewhat bigger files and/or stream rates. But I doubt this
will cause a rethink.
We have known for some time that the BBC was going to stop using Flash
at some stage. Dinky anticipated that change and get_iplayer no longer
supports Flash. The last version with Flash capability was v2.99.
HLS is a much more recent innovation than Flash. get_iplayer now has
its own built-in downloader which downloads HLS 2 or 3 times as fast as
Flash. HLS has been referred to as a legacy mode so it was always
likely that it would be removed eventually. The surprise was that HLS
was removed at the same time as Flash.
It is unrealistic to expect the BBC to restore HLS or Flash.
I have not seen any comments here which suggest that anyone is unhappy
with HVF. get_iplayer uses the same built-in downloader as for HLS.
The BBC's full list of HVF modes is set out in a table in this document.
https://www.bbc.co.uk/rd/blog/2015-07-the-development-of-new-video-factory-profiles-for-bbc-iplayer
What I think a number of people here would like to see is the addition
of one more High H.264 profile mode to that list, namely 1280x720p 25fps.
The BBC refers to viewing tests it has carried out, "using a range of
content and included clips, from popular shows such as Strictly Come
Dancing, East Enders and Top Gear."
It concludes, "At around 3 Mbit/s a 960x540 profile at 50fps will be
made available to Connected TVs and set top boxes. The Elemental
encoders are used to convert the 1920x1080 interlaced content to 960x540
for progressive encoding at 50fps. Although the 960x540 profile has a
reduced spatial resolution compared to the outgoing 1280x720 at 25fps,
subjective assessments shows it delivers significantly better pictures
on TV screens across a wide range of popular content (such as EastEnders
and Top Gear) due to its higher frame rate. The 50fps, 1280x720 profile,
however, will be available to those with 5Mbit/s broadband connections.
"Additional lower bit-rate profiles will be made available to computers
on wifi. This enables video playback to continue, even when an
individual's available bit-rate is reduced by users sharing a
connection. These profiles will also cater for similar bit-rate
restrictions on public wifi connections."
I accept that there is a trade off between resolution and frame rate.
With differential encoding schemes like H.264, at a higher frame rate
the changes between frames are smaller, so there is less to encode.
Even so, for the uncompressed video the resolution at 50fps would need
to be reduced to 905x510p to give the same bit rate as 1280x720p at 25fps.
For that reason I find it surprising that 960x540p at 50fps "delivers
significantly better pictures on TV screens across a wide range of
popular content (such as EastEnders and Top Gear) due to its higher
frame rate" than 1280x720p at 25fps but the BBC has done the viewing
tests and I have not.
More importantly BBC Four and to a lesser extent BBC 2 have a lot of
programmes about paintings, sculpture, architecture and nature where
there is a lot of fine detail and little motion. Intuitively such
programmes would not benefit from the higher frame rate but would
benefit from the higher resolution. There is no mention in the blog
that such programmes were included in the viewing tests, and they ought
to have been.
Best wishes
Richard
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