Sorry for crossposting, but whoever's running the public-inbox.org mirror,
please get it fixed.
Jan
On Nov 07 10:05:55, sox-devel+ow...@public-inbox.org wrote:
> Hi, this is the Mlmmj program managing the <sox-de...@public-inbox.org>
> mailing list.
>
> The message from <h...@stare.cz> with subject "Re: [SoX-users] how to
> interpret tell_off, and the right way to use sox_seek" was unable to be
> delivered to the list
>
> (The denied message is below.)
> Date: Tue, 7 Nov 2017 09:50:36 +0100
> From: Jan Stary <h...@stare.cz>
> To: sox-us...@lists.sourceforge.net
> Subject: Re: [SoX-users] how to interpret tell_off, and the right way to
> use sox_seek
> Reply-To: sox-devel@lists.sourceforge.net
>
> > First, it reads (which presumably moves the file pointer forwards),
> > then it seeks back to where it was.
> > I've verified in gdb that it actually does call sox_seek() (again and
> > again and again, but not forever). I have also verified in gdb that
> > it is reading the same samples.
>
> Ah, I see what your problem is now.
>
> > So sox_seek() is definitely being called, and definitely working.
> > But nevertheless, the reading done after the seeking eventually fails.
>
> Here is my slight rewrite of your example:
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <err.h>
> #include <sox.h>
>
> int
> main(int argc, char **argv)
> {
> sox_format_t *s;
> int32_t buf[1024];
> ssize_t r;
> int i;
>
> if (argc < 2)
> errx(1, "usage: ./soxseek input");
> if (sox_init() != SOX_SUCCESS)
> errx(1, "Cannot init libsox");
> if ((s = sox_open_read(*++argv, 0, 0, 0)) == NULL)
> errx(1, "Cannot open `%s'", *argv);
> for (i = 1; (r = sox_read(s, buf, 1024)) > 0; i++) {
> printf("[%04d] %zd samples, starting with %0x\n", i, r, *buf);
> if (sox_seek(s, 0, SOX_SEEK_SET) != SOX_SUCCESS)
> errx(1, "Cannot seek");
> }
> /* No way to test for sox_read() error */
> return 0;
> }
>
> (Note how I don't use sox_site_t for the sox_read() return value,
> because it does not exist, eventhough that's what libsox(3) documents.)
>
> $ sox -n /tmp/file.wav synth trim 0 $((1024 * 1000))s
> $ cc -o soxseek soxseek.c -lsox -I/usr/local/include/ -L/usr/local/lib
> $ ./soxseek /tmp/file.wav
> [0000] 1024 samples, starting with 0
> [0001] 1024 samples, starting with 0
> [....]
> [0999] 1024 samples, starting with 0
> [1000] 1024 samples, starting with 0
>
> So I think you are right. It does seek back to the begining of the sine wave
> (thus reporting 0 as the first sample value in the buffer), but it gets
> exhausted at EOF anyway. I suspect now it is a bug in sox_seek()
> if we are calling it right.
>
> > Certainly if you do analogous coding with calls to fread() and
> > fseek(), it would not terminate.
>
> Yes, the following will read the same file forever:
>
> #include <unistd.h>
> #include <fcntl.h>
> #include <stdio.h>
> #include <err.h>
>
> int
> main(int argc, char **argv)
> {
> int fd;
> int32_t buf[1024];
> ssize_t r;
> int i;
>
> if (argc < 2)
> errx(1, "usage: ./seek input");
> if ((fd = open(*++argv, O_RDONLY)) == -1)
> err(1, NULL);
> for (i = 1; (r = read(fd, buf, 1024)) > 0; i++) {
> printf("[%04d] %zd samples, starting with %0x\n", i, r, *buf);
> if (lseek(fd, 0, SEEK_SET) == -1)
> err(1, NULL);
> }
> return (r != 0);
> }
>
>
> > What i'm trying to do now is to determine the correct way to use
> > sox_seek() if i am using it incorrectly. If i'm using it correctly,
> > then i would like confirmation of my characterization (that it has
> > some internal counter which is decremented until it hits zero).
>
> I share your suspition now.
>
> > (I did have a signal processing problem that i was considering
> > earlier, but that's not relevant now because i avoided the sox_seek
> > issue by rearranging the computation. So i can do my dsp, but i do
> > wonder about correct usage of sox_seek.)
>
> Should we move this to sox-devel?
>
> Jan
>
>
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