[NUT-devel] Main file loop

[Michael Niedermayer]

Hi

On Sat, Nov 04, 2006 at 04:30:49PM +0200, Oded Shimon wrote:
> In my opinion it is all wrong.
> This loop deals with legality of file, not how the demuxer reads the file.
> 
> Current:
> > file:
> >     file_id_string
> >     while(!eof){
> >         packet_header, main_header, packet_footer
> >         reserved_headers
> >         for(i=0; i<stream_count; i++){
> >             packet_header, stream_header, packet_footer
> >             reserved_headers
> >         }
> >         while(next_code == info_startcode){
> >             packet_header, info_packet, packet_footer
> >             reserved_headers
> >         }
> >         if(next_code == index_startcode){
> >             packet_header, index_packet, packet_footer
> >         }
> >         if (!eof) while(next_code != main_startcode){
> >             if(next_code == syncpoint_startcode){
> >                 packet_header, syncpoint, packet_footer
> >             }
> >             frame
> >             reserved_headers
> >         }
> >     }
> 
> 
> The way it should be in my opinion:
> file:
>     file_id_string
>     while(!eof){
>         packet_header, main_header, packet_footer
>         for(i=0; i<stream_count; i++){
>             packet_header, stream_header, packet_footer
>         }
>         reserved_headers
>         while(next_code == info_startcode){
>             packet_header, info_packet, packet_footer
>         }
>         reserved_headers
>         if(next_code == index_startcode){
>             packet_header, index_packet, packet_footer
>         }
>         if (!eof) while(next_code != main_startcode){
>             packet_header, syncpoint, packet_footer
>             do {
>                 frame
>             } while (next_code == framecode)
>             reserved_headers
>             if (realtime_stream) {
>                 while(next_code == info_startcode){
>                     packet_header, info_packet, packet_footer
>                 }
>                 reserved_headers
>             }
>         }
>     }
> 
> 
> 1. no reserved headers allowed until end of stream headers
>    this offers absoloutely no disadvantage in extendibility:
>    a. new packets can still be written afterwards.
>    b. if it is so important that it needs to be written either next to the 
>    main header or next to the streams, it can be written inside the main 
>    header or inside the stream headers (reserved_bytes)

no, there are cases where it makes sense
think about error correcting packets (with reed solomon parity symbols for
example) yes its a silly example but its not entirly unrealistic
and such error correcting packets pretty much must be after the packet they
apply to as the info is needed for parsing of later packets
placing the stuff in the packet might cause some problems with future
extendability ...
another similar example would be a signature to proof that a header hasnt
been tampered with ...

also what is the problem with allowing such extra headers there? just
disallowing something because we dont see an immedeate use is not good
design

the same points apply to the other cases where you want reserved_headers
removed


[...]
> 3. syncpoints must be written after any non frame packets, before any 
>    frame packets.

i think that is required by other parts of the spec already

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or copy any book
Today you'd get arrested for mere telling someone where the library is