Quoting Diego Biurrun (2016-08-26 09:48:26) > On Thu, Aug 25, 2016 at 06:36:45PM -0500, Burt P. wrote: > > On Thu, Aug 25, 2016 at 5:46 PM, Jean-Baptiste Kempf <j...@videolan.org> > > wrote: > > > On 25 Aug, Burt P. wrote : > > >> HDCD coding is hidden in some CD audio, but not all, and using it is > > >> completely optional. > > > > > > But you can detect that, cannot you? > > > > Yes, but it requires scanning the whole audio to know if you will be > > using peak extend. > > PE requires and 6dB of room at the top for the expanded peaks. > > So you have to make two full passes, or just always apply -6dB to all > > 16-bit audio in case HDCD/PE appears. > > The current implementation does the latter, because we only get the > > audio one frame of a few thousand samples at a time. > > We need at least one or two seconds, 44100-88200 samples, to know we > > will catch an HDCD packet. > > There are some HDCD-CDs where only one track had HDCD encoding, > > because it was a compilation or something. > > In this case, you could have a single file flac+cue being processed, > > and not know for 20 minutes into the audio that you need room for peak > > extend. > > > > Audio players can scan ahead, and choose to use HDCD processing or not. > > They can even enable-disable per track, or when seeking, by scanning > > ahead or behind a couple seconds, without the listener noticing in > > most cases. > > For avconv/ffmpeg (at least the cli), however, I think it is best left > > to the user. > > I'm with j-b on this one. If the filter is optional, it will be left > out in 99% of cases. It sounds like you are optimizing for a rare edge > case and sacrificing ease of use and better quality in 99% of cases for > it...
And do you have any practical suggestion about how this is to be accomplished? As I understand, this kind of audio is incredibly rare, so you cannot just impose a delay on all PCM decoding just because of the tiny number of files that might need it. I can imagine a bitstream filter that would detect it and perhaps insert appropriate side data signalling that the extra information is present, but this is still awkward and fragile. FWIW the filter approach seems acceptable to me. -- Anton Khirnov _______________________________________________ libav-devel mailing list libav-devel@libav.org https://lists.libav.org/mailman/listinfo/libav-devel
