Correction, the flac command-line does create a 40-byte Vorbis comment by default. I just never noticed it before. I’ve been using —no-padding all these years for minimal file sizes without realizing that I could save another 40 bytes.
Anyway, since metaflac can remove the Vorbis comment using the standard library, then you should be able to create a solution without modifying libFLAC. Brian On Feb 4, 2018, at 12:43 AM, Brian Willoughby <bri...@audiobanshee.com> wrote: > Gabriel, > > metadata_has_vorbis_comment is a FLAC__bool which defaults to false. There > should be no reason to modify stream_encoder.c, but just modify the caller. > > The following command: > > metaflac —remove —block-type=VORBIS_COMMENT —don’t-use-padding > > … will remove Vorbis comments from existing files, so is must be legal > without modifying the library. metaflac can clearly create a new FLAC file > without the Vorbis comment. > > I use the flac command-line, and I never get Vorbis comments in the files > that I create. Perhaps you are using another tool which assumes Vorbis > comments are needed. > > > The FLAC algorithm is not dependent upon sample rate. AIFF has an 80-bit > floating point type for sample rate, so it should be able to handle 40 MHz. I > assume that any AIFF can be converted to FLAC losslessly, but I have not > tested whether certain sample rates are rejected. FLAC itself only supports > sample rates up to 655,350 Hz, so you may have a problem there unless you > “lie” about the sample rate when creating the file. Maybe you could just > establish a private convention to divide the sample rate by 100 to make yours > fit. 40 MHz would map to 400 kHz, 10 MHz would map to 100 kHz, and 5 MHz > would map to 50 kHz. > > > You’re probably asking for trouble if you try to reuse an encoder. It seems > like there would always be some risk that details from the previous file > would bleed through into the next. Have you benchmarked allocation and > initialization? Is it really that slow? In order to reuse an encoder, you’ll > need to overwrite all state variables, and I don’t see how that could be much > faster than simply allocating them anew. Perhaps you could allocate groups of > encoders at once, if that would speed the process. > > > On Feb 1, 2018, at 4:29 AM, Gabriel Corneanu <gabrielcorne...@gmail.com> > wrote: >> Hello all >> >> I am using libFLAC in a corner application, compressing a lot of small >> signals. >> First is a general question: in our application we have signals in range >> 5-10 MHz, potentially 40MHz! Is there any potential problem with that?? The >> mac sample rate is limited in flac, but it doesn't really seem to be a >> problem. >> The output is stored as blob in a sqlite database, it never needs to be a >> valid audio file outside our application. >> In my tests, the signals are compressed very well, much better than general >> compression libraries like zlib, zstd, etc. >> >> Now other small issues; I also made some tickets about them, but I thought >> asking here might be better. >> >> 1. I would like to avoid saving vorbis comment, by default ~40 bytes. Right >> now the only option is to modify stream_encoder.c, see >> "metadata_has_vorbis_comment". >> >> 2. Speed is very important, therefore I would like to reuse an encoder >> without re-initializing everything. >> Ideally I would like 2 (exported) functions: "flush" and "restart". >> "Flush" is self-explanatory, should properly end the encoding. I could split >> myself "flush" from "finish", it looks relatively simple. >> "Restart" should keep all current settings, generate a new stream header and >> clear everything for encoding a new signal. >> It' clear that current settings, re-creating windows, cpu-dependent >> functions, etc could be kept around. >> I was not quickly able to extract all the necessary initialization from >> "init_stream_internal_" into a new "FLAC__stream_encoder_restart" function. >> >> Regards, >> Gabriel Corneanu _______________________________________________ flac-dev mailing list flac-dev@xiph.org http://lists.xiph.org/mailman/listinfo/flac-dev
