Find flac sample rate in VBA

2021-01-31 05:00:39

I want to query some flac files with VBA code to get their duration

From testing about 50 flac files the 3 bytes at offset 23 after "fLaC" seem to correctly return the Number of Samples.
Then this must be divided by the sample Rate for total number of Seconds
But I cannot locate the sample rate in the Stream info block, where I believe it is stored.

Can anyone help me find this?

Re: Find flac sample rate in VBA

Reply #1 – 2021-01-31 13:05:30

Is this what you are looking for?
METADATA_BLOCK_STREAMINFO
<20>   Sample rate in Hz

https://xiph.org/flac/format.html#metadata_block_streaminfo

Re: Find flac sample rate in VBA

Reply #2 – 2021-01-31 15:30:18

Probably going to be easier and more reliable to use a library like libflac or ffmpeg to get the file metadata rather then try to parse the streams yourself. 

Re: Find flac sample rate in VBA

Reply #3 – 2021-02-01 02:57:32

I am using metaflac.exe but want to get the duration into my own app, rather than Shell to DOS window.
I've spent a few hours reading the info in that link but can't understand it.  What are numbers inside  <> chars?
I did  a bit-compare of a 44100 and 96000 and found byte offset 29 (after fLaC) had the last 4 bits as 1001 for 44100 and 1011 for 96000. But this wasn't consistent with "0111" often found.
Can someone better interpret that link and explain it to me ?  Or tell me how I might find the sample rate. I have seen code for this but it's in a format (language) I don't know.

Re: Find flac sample rate in VBA

Reply #4 – 2021-02-01 03:11:07

^^^ Metaflac calls libflac, which you can also do directly from your program.

Re: Find flac sample rate in VBA

Reply #5 – 2021-02-01 04:14:01

That sounds ideal. Would you have any examples of calling libflac from VBA ?

Re: Find flac sample rate in VBA

Reply #6 – 2021-02-01 05:15:27

The sampling rate is at offset 12h. It is backwards in big-endian format.

Re: Find flac sample rate in VBA

Reply #7 – 2021-02-01 06:26:07

Thanks very much.  Off to see how I can implement that.

Re: Find flac sample rate in VBA

Reply #8 – 2021-02-01 07:46:46

Sorry, I'm just not finding it.. perhaps compounded by the big endian translation (which I'm just figuring out).
If the image works, which bytes are offset 12h ?  It should convert to 44100.

Re: Find flac sample rate in VBA

Reply #9 – 2021-02-01 08:06:01

These.

Re: Find flac sample rate in VBA

Reply #10 – 2021-02-01 22:10:40

Brilliant. All sorted. Thanks very much j7n

Re: Find flac sample rate in VBA

Reply #11 – 2021-02-03 07:20:54

I note this in the flac site

<3>    (number of channels)-1. FLAC supports from 1 to 8 channels

Does this mean byte 3 should be 1 if the file is mono (single channel) ? 

Re: Find flac sample rate in VBA

Reply #12 – 2021-02-03 08:25:40

Quote from: Empire on 2021-02-03 07:20:54

(number of channels)-1. 

1 - 1 = 0 for a single channel, up to 7 for eight channels.

Re: Find flac sample rate in VBA

Reply #13 – 2021-02-03 09:40:03

Not a whole byte but 3 bits just after the sampling rate at 14h. The remaining 1 bit is the most significant of the bit depth.

Re: Find flac sample rate in VBA

Reply #14 – 2021-02-03 21:53:07

Thanks muchly it's a big help understanding the info at https://xiph.org/flac/format.html.
One other question - where it shows
METADATA_BLOCK_STREAMINFO
<16>    The minimum block size (in samples) used in the stream.

Does this mean the 16 bits immediately following "fLaC"  ?

Re: Find flac sample rate in VBA

Reply #15 – 2021-02-03 21:57:56

After fLaC and 4 additional bytes of block_type and its length.