quartz: Detect and skip id3v2 header in mpeg splitter

Maarten Lankhorst m.b.lankhorst at gmail.com
Fri Mar 14 13:08:42 CDT 2008

Hi Chris,

2008/3/14, Chris Robinson <chris.kcat at gmail.com>:
> 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).
Considering it's metadata that doesn't have any effect for the next
stages, it shouldn't be sent upstream. It should just be dropped
locally. I missed the main splitter function, I'll fix that one too.


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