> >>Am I ever likely to encounter an MPEG Audio file which will contain
AUDIO
> >>frames which differ in VERSION, LAYER, SAMPLERATE and/or CHANNELS? Eg.
> >>Some frames are 48KHz and other frames are 44.1KHz ...or some frames in
> >>Stereo, some in Joint-Stereo?
a change of LAYER or SAMPLERATE requires a restart of the decoder.
Excellent information.
I notice you did not mention VERSION or CHANNELS ...Given a LAYER change
will trigger a restart it seems logical to presume a VERSION change would
also trigger a restart even if the change was Ver1/Lyr1 -> Ver2/Lyr1
Would you care to comment on CHANNEL changes ...even if your answer is
"don't know" I would consider that to be helpful feedback.
> Thanks, I too use razorlame, and also have no idea what short or long
> blocks are - and google isn't helping much either. LOL
IIRC, the audio data that belongs to each MPEG-1 layer III audio header
(in fact, the frame header can be located just in the middle of the
audio data it belongs to)
:O
A frame header can exist in the middle of an [a pair of] audio frame[s]??
Could you explain a little more on that - it seems very important to my util.
If my file has only TWO [a pair of] audio frames (unlikely, but valid)
...the file can/will look like "AUDIO_DATA -- HEADER -- AUDIO_DATA"
...surely lack of a header at the start of the file will mean the first
block of audio data cannot be found by the decoder?
Or do you mean that there would be two [a pair of] audio frames which each
contained half of the data required to recreate the original sound?
Do you have a test file which I can throw at my util for testing please?
(or instructions for making one)
is parted into 2 halves AKA granules. Those in
turn are parted into n (frequency) subbands, which can consist of either
1 long or 3 short blocks (windows) of samples (it's even possible to have long
blocks in the lower and short blocks in some upper subbands). The former
have a better frequency resolution, the latter a better time resolution
(eg to reduce pre-echoes). Try a percussive sound like from a
glockenspiel or triangle to hear the difference when short blocks are
disabled.
Perfect, thank you.
Jacob
BC
