[vlc-devel] more going backwards ...

John Michael Zorko j.zorko at att.net
Sun May 25 02:00:51 CEST 2003

Hello, all ...

I've modified input_thread_t to have a pf_demuxdrop member (which i'm 
thinking would normally act just like pf_demux, except that it would 
call something in the access module to allow for seeking forward or 
backward, and optionally _not_ put whatever data_packet_t's it makes 
into the FIFO, the idea being to allow for "drop 3 MP3 frames and play 
5" functionality).  I've also implemented the pf_demuxdrop (DemuxDrop) 
in the vlc_root/modules/mpeg/audio.c MP3 module, but i've questions:

1. off_t's and seekable things ... would it makes sense to add an off_t 
member to data_packet_t, this being the position in the file the packet 
lives at?  Basically, from the demux module in my new DemuxDrop(), I 
need to know the off_t of the current packet so I can have a start 
position for seeking for the next seekable thing (i.e. MP3 frame, start 
code, sequence header, GOP, etc.)  I'm not sure if I can rely on the 
selected_area->f_tell member ...

2. how to do this in a media-agnostic way ... for the short term, we 
need to be able to seek to any MP3 frame relative to the current one 
the demux module is handling (i.e. "seek back 10 MP3 frames in the 
file" or "seek forward 5 MP3 frames in the file") but ... well, 
data_packet_t's hold MP3 frames just fine, but if we ever want to seek 
on anything that may be bigger than one data_packet_t (i.e. a GOP, or 
an I-frame perhaps), this is where it kinda gets a bit messy, as one 
GOP or one I-frame may actually live in 4, 5.5, 8, etc, 
data_packet_t's, right?  I want to avoid feeding the decoder module 

Thoughts?  I want to get this mostly working this weekend, even if it 
only provides a starting point for further work down the road (and i'd 
love to stay involved in said further work ... hacking VLC is fun!)



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