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