TV Audio Bitrates
richard22j at zoho.com
Tue Sep 5 09:26:12 PDT 2017
Sent: Saturday, August 26, 2017 00:04 I wrote
>On 25/08/2017 16:28, Vangelis forthnet wrote:
>>But still the "Not so" part of his post stands true for various pids
>>outside the main BBC TV channels...
>> Just try (with 3.02)
>> get_iplayer --type=tv --pid=p059b38x --tvmode=hvfsd
>> (pid expires in 2 days) and you'll discover it fetches as a 128kbps hvf*
>> mode... One other oddity for this pid is it's not available as legacy
>> hls* (/flash*) tvmodes, only dvf*/hvf*.
>> I guess a better choice of wording would be:
>> "GiP 3.02 tries to download every hvf* tvmode with a 320kbps audio
>> stream, whenever that one is available on the CDN server"
>As you say, this example is outside the main BBC channels, and more
>specifically not a regular broadcast. I am sure you have done more analysis
>than I, but to a large extent regular broadcasts have PIDs beginning with b
>and special programmes such as Red Button or clips have PIDs beginning with
>p. In the case of Red Button programmes there is usually no HLS mode. I
>think this is the first time I have seen a 125kbit/s audio rate for a TV
>programme but that may be because when there has been no HLS mode I have
>usually used HVFxsd rather than a 50fps mode. That up to now has given
>96kbit/s HE-AAC v1 in contrast to 96kbit/s AAC-LC for HLShd. The video
>also has some unfamiliar settings.
After posting that I saw that the programme you were referring to was indeed
a Red Button programme. I have now downloaded the Red Button coverage of
the cross-country phase of the Burghley CCI**** horse trials on Saturday,
b09544c6 in v3.02. There were no HLS modes other than HLSvhigh. The audio
bit rate for HVFxsd was 125kbit/s.
For these programmes I used to use hvfxsd5 which was usually an Akamai HTTP
CDN. The number of HVFxsd CDNs seems to have been reduced. It used to be
about 8 and was 3 for this programme. As the programme was not in my cache
I could not use --info but I was able to download it. hvfxsd1 and hvfxsd3
both gave about 17Mbit/s and hvfxsd2 (the last I tried) about twice that.
To sum up
1. I was wrong about the distinction between b and p prefixes for PIDs.
2. The rule for audio bit rate seems to be that 320kbit/s audio will be
used for all HVF modes including HVFlow for programmes which have been
broadcast on main stream television channels and for Red Button programmes
it will be 125kbit/s.
125kbit/s audio for Red Button programmes is an improvement over the
96kbit/s HEAAC v1 which used to be used for some HVF modes and avoids the
problem of loss of high frequencies with players which do not support SBR.
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