[mpg123-users] MPG123_DONE occurring in different place after seek?

[Darren Lo <dar...@gm...>]

Greetings,

I'm seeing something unexpected with seeks, and I'm not sure if I'm
doing something wrong. The situation is as follows: I open a gaplessly
encoded MP3 with mpg123_open, call mpg123_read until I get
MPG123_DONE, and add up the total number of decoded bytes. This number
matches the length of the original PCM audio. Then I seek to offset 0
and repeat the process. This time MPG123_DONE will be returned in a
different, later place (i.e., the new total number of bytes is
larger). Further repetitions always give the new, larger number.
However, I would expect that MPG123_DONE should always be returned
after the same number of bytes.

Here is an example of what I mean:

  for (iteration = 1; iteration <= maxiter; iteration++) {
    printf("Decoding %s (time %d of %d)...\n", filename, iteration, maxiter);
    total = 0;
    do {
      mpg123_err = mpg123_read(mh, buf, sizeof buf, &written);
      total += written;
    } while (mpg123_err != MPG123_DONE);
    printf("Got %u bytes in all.\n", total);
    mpg123_seek(mh, 0, SEEK_SET);
  }

The output of this is:

Decoding yuka.mp3 (time 1 of 5)...
Got 12296384 bytes in all.    // correct value
Decoding yuka.mp3 (time 2 of 5)...
Got 12298940 bytes in all.    // incorrect
Decoding yuka.mp3 (time 3 of 5)...
Got 12298940 bytes in all.
(...)

If I compare the PCM output for the runs, they all compare identical
except for extra data at the end for runs 2 and up.

So, what is wrong here?