Re: About mad_stream_skip

On Sep 21, 2004, at 1:33 PM, Francis Labonte wrote:
> I have a question about mad_stream_skip.
>
> If I call this function, would if be correct to call mad_stream_sync 
> after?

Probably not.

The purpose of mad_stream_skip() is to tell the decoder to skip a 
number of bytes in the stream because they do not contain audio data. 
The most common use for this is to skip embedded ID3 tag information. 
Bytes skipped may cross stream buffer boundaries; MAD_ERROR_BUFLEN is 
returned as appropriate, so your stream refilling code need not be 
aware that bytes are being skipped. After the indicated number of bytes 
have been skipped, the decoder assumes the next byte begins a sync 
word. If not, MAD_ERROR_LOSTSYNC is returned as usual and the sync word 
will be located automatically on the next call.

Since the decoder does it automatically, it's almost never necessary to 
call mad_stream_sync() yourself.

> Actually, mad_stream_skip does'nt  care about the skip offset (well, I 
> think...).  I would expect that if I call sync after skip, It will try 
> to sync starting from the new position (position + skip offset).

What actually happens is the skip is deferred until the next frame is 
decoded, but the sync happens immediately. The reason is that skips may 
cross stream buffer boundaries, but the sync search happens only within 
the current buffer.

-- 
Rob Leslie
[email protected]