[mpg123-users] Trying to understand MPG123_NEW_FORMAT

[Martin G. <mar...@gm...>]

Greetings

I am trying to do the best I can when reading of a half-broken MP3 file 
where mpg123_read() returns MPG123_NEW_FORMAT three times, and each 
time, I ask mpg123_getformat() what the new format is.
The first time it says the stream now has one channel, then it happens 
again and getformat() says it has 2 channels again.

Specifically, I'm asking for 10240 frames of pairs of shorts and on 
shorter reads the code retries until it has the required block of data:

mpg123_read(40960 bytes) returns MPG123_OK with 40960 bytes written
mpg123_read(40960 bytes) returns MPG123_NEW_FORMAT with 24576 bytes
    and mpg123_getformat() says it has 1 channel
mpg123_read(16384 bytes) returns MPG123_NEW_FORMAT with 1536 bytes
    and mpg123_getformat() says it has 2 channels
mpg123_read(14848 bytes) returns MPG123_OK with 14848 bytes
mpg123_read(40960 bytes) returns MPG123_NEW_FORMAT with 0 bytes,
    still saying it has 2 channels
mpg123_read(40960 bytes) returns MPG123_OK with 40960 bytes
    and from there it carries on working normally

My question is whether the new format applies to the data returned by 
the call that returned NEW_FORMAT, or whether the new format applies to 
data returned by the successive calls to mpg123_read (i.e. are the 24576 
bytes mono data, or the 1536 bytes?)

I've read the documentation many times, but can't figure out whether 
MPG123_NEW_FORMAT's format is retrospective or futuristic.
Any clues would be welcome.

     M