Speex dev - May 2006 - Determining length of speex file speech

Hello,

I would like to run a script over a speex file which determines, how
long the speech contained in the speex file is.
So I run through the ogg file, skip the first two ogg _pages_ (speex
header and comment header, both contain IMHO only 1 ogg _packet_), and
then count in any ogg page the number of the ogg _frames_ (which, unless
I used -nframes while encoding, which I did not), and multiply this with
.02 (20 milliseconds).
I did this by hand, for example on the file I send yesterday when asking
about the noise, so the output of the program is:

$ readspx spfe49_1-small.spx
speex header
Version:1.1.12
rate:44100
mode:2
mode_bitstream_version:4
nb_channels:2
bitrate:-1
frame_size:640
vbr:0
frames_per_packet:1
extra_headers:0
Page #2: 1 packets.
Page #3: 45 packets.
Page #4: 45 packets.
Page #5: 45 packets.
Page #6: 45 packets.
Page #7: 45 packets.
Page #8: 45 packets.
Pages: 8
Packets: 272

Calculating things per hand here 6*45 speex frames, so the speech length
should be 5.4 seconds. Unfortunately this is overestimated:

$ time speexdec spfe49_1-small.spx
Decoding 44100 Hz audio using ultra-wideband (sub-band CELP) mode (stereo)
Encoded with Speex 1.1.12

real    0m3.992s
user    0m0.112s
sys     0m0.020s

So my questions are: What does the "frame_size: 640" mean (the
information was simply read out with speex_header->frame_size).
Why does my algorithm for calculating the length of the speech in a
speex file not work?
How is the number of ogg _packets_ per ogg _frame_ set by the encoder
(commandline, file-based)?

Ciao,

Bj?rn


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On Tue, May 16, 2006 at 03:29:47PM +0200, Bj?rn Thalheim
wrote:
> 
> I would like to run a script over a speex file which determines, how
> long the speech contained in the speex file is.
> So I run through the ogg file, skip the first two ogg _pages_ (speex
> header and comment header, both contain IMHO only 1 ogg _packet_), and
> then count in any ogg page the number of the ogg _frames_ (which, unless
> I used -nframes while encoding, which I did not), and multiply this with
> .02 (20 milliseconds).
> I did this by hand, for example on the file I send yesterday when asking
> about the noise, so the output of the program is:
> 
> $ readspx spfe49_1-small.spx
> speex header
> Version:1.1.12
> rate:44100
> mode:2
> mode_bitstream_version:4
> nb_channels:2
> bitrate:-1
> frame_size:640
> vbr:0
> frames_per_packet:1
> extra_headers:0
> Page #2: 1 packets.
> Page #3: 45 packets.
> Page #4: 45 packets.
> Page #5: 45 packets.
> Page #6: 45 packets.
> Page #7: 45 packets.
> Page #8: 45 packets.
> Pages: 8
> Packets: 272
> 
> Calculating things per hand here 6*45 speex frames, so the speech length
> should be 5.4 seconds. Unfortunately this is overestimated:
Hi Bj?rn,

The number of pages is irrelevent. Pages are just the container that
stores packets, and the number of packets in each page could vary. You
only need to keep track of the number of packets in the file. Then:

encoded_speex_frames = (frames_per_packet * Packets)
                     = 1 * 272
                     = 272

audio_samples = encoded_speex_frames * frame_size
              = 272 * 640
              = 174080

duration = audio_samples / rate
         = 174080 / 44100
         = 3.947

cheers,

Conrad.

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