quartz: Detect and skip id3v2 header in mpeg splitter

[Chris Robinson]

On Friday 14 March 2008 10:29:34 am Maarten Lankhorst wrote:
> Hi Chris,
>
> 2008/3/14, Chris Robinson <chris.kcat at gmail.com>:
> > On Thursday 13 March 2008 09:01:53 pm Maarten Lankhorst wrote:
> >  > If read from a file source, ID3 v2 tags might be incorrectly parsed by
> >  > the head_check. This patch skips the whole tag altogether.
> >
> > I'm not sure this is completely correct. The main splitter function
> > detects the presense of an MP3 header at the start of a sample it's
> > sending to set the sample's sync point attribute. Since the ID3 tag is
> > not a sync point, this causes the first sample to not be set as a sync
> > point, and it would be unlikely that a following sample would, under
> > normal circumstances, contain an MP3 header at the start either. This
> > could cause sensitive codecs to never find a sync point.
>
> In general the tag is not a sync point, but some data behind it
> accidentally may be parsed as such. Even if it didn't, the tag is
> generally a few 100 (or about 1000 in my case)  bytes in size. Reading
> all those bytes individually and moving them all 4 times doesn't seem
> really optimal. Skipping the amount of data that is set in the size
> buffer causes it to immediately find the first mp3 header.

Correct, but the patch only handles when the pin connection happens. The main 
splitter function will go through the start of the data again, and find the 
ID3 tag again, where it doesn't find the header to set the sync point (unlike 
the pin-connection, it doesn't continue to search forward and will just send 
it as is without the sync point attribute, though).

The following filter (acmwrapper or a native one) will also get the ID3 tag 
and will have to be able to handle it, otherwise it'll fail just like the 
splitter would.