[FFmpeg-trac] #4441(avfilter:closed): support HDCD
FFmpeg
trac at avcodec.org
Thu Aug 4 06:05:48 EEST 2016
#4441: support HDCD
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Reporter: calestyo | Owner:
Type: enhancement | Status: closed
Priority: wish | Component: avfilter
Version: git-master | Resolution: fixed
Keywords: hdcd | Blocked By:
Blocking: | Reproduced by developer: 1
Analyzed by developer: 0 |
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Comment (by calestyo):
Great :)
Does this also include the information whether HDCD was detected at all?
I.e. what you proposed for example for ffprobe?
Oh and you mentioned some yet unknown extra features of HDCD...
You think there are any references where more about that things could be
found out?
Over time I collected some docs about HDCD... perhaps they contain more
info.
Could upload them here in case you're interested.
I also got a manual to the Model Two HDCD A/D Converter D/A Converter
Digital Processor... some HDCD guru once told me it would contain some
valuable information. Could send it to you via mail.
Quoting a mail from the same guru:
>Attached is the requested manual. Everything is pretty easy to figure out
except one thing -- the exact curve for the Peak Extend function. All of
the implementations I've seen on the internet appear to simply eyeball the
graph in the AES paper and make a close guess.
>Not the best way to do it, but better than nothing. Additionally, the
maximum expansion possible is +6 dB for PE (one bit), and -4 dB (maximum!)
for Low-Level Extension. So we are only talking about turning 16 bit data
into 17 bits, or at very most and only on occasion, 17.5 bits. Yet
everyone puts the result into 24-bit containers. I don't suppose there is
much choice...
>The filter encode flag is in the "subcode" as that was part of the
original plan. However Ed Meitner (then at Museatex) had already patented
a switchable playback filter so Pacific Microsonics couldn't use it.
>They must have found that out very late in the process as the "sub-code"
for the filter is on every disc, showing which filter was used for the
encoding side. But this was never, ever decoded. There was only one
playback filter ever used on any HDCD player - period. Everybody is
confused by this and speculates about what the "two filters" are. The
answer is "they aren't". There is only one filter. It's OK sounding, but
not as good as more modern minimum-phase filters that are optimized for
superior time-domain performance.
>Finally, while the engineering of the HDCD system was excellent, the
marketing was total baloney. If the mastering engineers turned off ALL of
the features that required decoding, the disc would still light up the
HDCD light on the player. This is complete nonsense as there is absolutely
nothing to decode. They were simply trying to scare the consumer into
believing that they needed to buy an HDCD player. (That is just one
example of many, most of them far more deceitful.)
So perhaps that unimplemented feature is one of those you mentioned to be
"missing"?
Also I once read that HDCD features could basically be enabled any time in
each track (though most implementations only teste the first few seconds),
and that features could differ from track to track on a CD (which is of
course natural, as HDCD is not CD specific).
So any auto-detection code might already need to scan the whole data?!
Cheers,
Chris.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/4441#comment:33>
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