[vorbis] Using vorbisfile with an in-memory file instead of FILE*

[Michael Smith]

>Is it planned to add const?
>And maybe initial could be changed to const void*, so you don't need a cast
>if you have for example an unsigned char*.

Not particularly planned. It wouldn't break (or otherwise change) anything
to add it, though. You don't need a cast here anyway.

Feel free to send in a patch if you think it's worthwhile (you might like
to see if there are other relevent places to add const qualifiers in
vorbisfile while you're doing so).

>
>Also, I tried to use an in-memory file with the following code, but that
>code hung in ov_open.
>I didn't setup the callbacks yet, but I thought that wasn't necessary
>because of the real (empty) file.
>Of course I'm going to setup callbacks in the future.
>When I use the fwrite, but not the rewind, it seems to work.
>When I use both fwrite and rewind, but not initial and initial size, it
>works also.
>What did I do wrong?

Can't say, since you haven't given all the relevent code here. If you gave
more code (specifically, that for get_data() and get_size(), I could give a
conclusive answer, though if those are complex it'd be better to just give
a simplified version of your code.

My best guess, based on what the code might be doing, is that you're
writing data to a file (this much is obvious) then 
  a) not rewinding, and giving buffers with initial and ibytes. ov_open()
will then read data from the buffer, and find that the file is at EOF, or..
  b) rewinding, and not giving extra buffers. Then ov_open() just reads
from the file as normal.

If you rewind AND specify initial/ibytes, then the raw data gets read in
twice, which isn't permitted (if this is the whole file, then you've
essentially given a physical bitstream containing two logical bitstreams
with the same serial number, which isn't allowed, so things fail. If it's
part of the file (or part of the file is in the memory buffer), then you're
corrupting the headers by sending them twice).

Giving a memory buffer, and an empty (length 0) file should work, though it
isn't a particularly sensible way to do things unless you have extremely
small files. Useful as a test, maybe, but go to using the callbacks ASAP.

Michael

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