On 2014-04-24 15:51:06 +0200, Niels Möller wrote: > [email protected] (Niels Möller) writes: > > > For a start, I implemented a *very* crude up-sampling, simply repeating > > each core sample twice. > > I've now tried the following experiment: > > Decode the core stream using unmodified libav, generating a 24-bit 48 > kHz file. Then apply this crude repeat-upsampling to this file, and > compute the sample-by-sample difference from the reference flac file. > Then I get, at the end of the file, > > 899059: 864 5116 -468 -145 357 > 899060: -2346 -4270 -923 -611 -157 > 899061: 2163 4161 1178 686 919 > 899062: -759 -4693 -1505 -1406 -1042 > 899063: 1254 4742 1153 995 697 > 899064: -3511 -7763 123 -1121 -28 > 899065: 3055 8669 -1419 1079 287 > 899066: -5100 -8364 1267 -1516 43 > 899067: 6608 6793 430 1237 413 > 899068: -4935 -6059 -849 -1720 -703 > 899069: 2974 8292 86 1522 390 > 899070: -3851 -7902 512 -1258 -56 > 899071: 5415 6983 -111 685 49 > > The residuals are both alternating in sign, and larger than what I get > when decoding the xll data, so I think this makes it clear that there > should be some decent filter for the upsampling. The residuals should > encode (mostly unaudible) audio contents in the frequency band from 24 > kHz to 48 KHz (and audio close below 24 kHz which was filtered out for > the core channels), and errors from the lossy encoding, but not > artifacts of bad upsampling.
You can repeat the experiment with avresample upsampled output to determine a close match for filter options. use '-i file -ar 96000 $filter_options ... out.au' Interesting filter options are probably filter length/type, -linear_interp search for AVAudioResampleContext AVOptions: in `avconv -h full` for all options. Janne _______________________________________________ libav-devel mailing list [email protected] https://lists.libav.org/mailman/listinfo/libav-devel
