[FFmpeg-trac] #4441(avfilter:closed): support HDCD

FFmpeg trac at avcodec.org
Thu Aug 4 06:05:48 EEST 2016


#4441: support HDCD
-------------------------------------+------------------------------------
             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            |
-------------------------------------+------------------------------------

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>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker


More information about the FFmpeg-trac mailing list