{"id":331,"date":"2006-09-13T18:55:37","date_gmt":"2006-09-14T01:55:37","guid":{"rendered":"http:\/\/multimedia.cx\/eggs\/my-app-a-day\/"},"modified":"2006-09-13T18:55:37","modified_gmt":"2006-09-14T01:55:37","slug":"my-app-a-day","status":"publish","type":"post","link":"https:\/\/multimedia.cx\/eggs\/my-app-a-day\/","title":{"rendered":"My App A Day"},"content":{"rendered":"

This ambitious software developer<\/a>, the Software Jedi, wants to write an app a day for a month and he is soliciting suggestions. <\/p>\n


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Here is one idea that I dreamed up just the other day as I was plodding through the hex dump of yet another freshly discovered, FourCC-chunked multimedia file format. This is the proposal– maybe he will find it interesting enough to write up in C#, maybe I will have to do it instead, or maybe someone else will beat me to it:<\/p>\n

A lot of multimedia files use what I like to call the “chunked-FourCC” format:<\/p>\n

\r\n  chunk 0\r\n  chunk 1\r\n   ..\r\n  chunk n\r\n<\/pre>\n
Chunks are formatted as:<\/p>\n
\r\n  preamble\r\n  payload\r\n<\/pre>\n
The preamble invariably consists of:<\/p>\n
\r\n  chunk identifier-- usually 4 ASCII chars (FourCC)\r\n  length\r\n<\/pre>\n
When I stumble on a new chunked-FourCC-type file format, I want to know all of the possible chunk types. I want a simple tool that could walk through all the chunks in the file and print the various types.<\/p>\n
At issue is the preamble format– sometimes the FourCC is first, sometimes the length is first; sometimes the length is big endian, sometimes it’s little endian; sometimes there is an extra “flags” component to the preamble; sometimes the length includes the preamble chunk, sometimes it doesn’t.<\/p>\n
So I am thinking of a utility where I can specify all of these parameters from the command line and the tool would print info about the chunks based on those instructions. A good starting point would be any Apple QuickTime (.mov) file. The chunk (“atom”) format is (and all multi-byte numbers are big endian):<\/p>\n
\r\n  bytes 0-3    atom size (including 8-byte size and type preamble)\r\n  bytes 4-7    atom type (ASCII chars, usually)\r\n  bytes 8..    data\r\n<\/pre>\n
There is also a special case for large atoms:<\/p>\n
\r\n  bytes 0-3    always 0x00000001\r\n  bytes 4-7    atom type\r\n  bytes 8-15   atom size (including 16-byte size and type preamble)\r\n  bytes 16..n  data\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
This ambitious software developer, the Software Jedi, wants to write an app a day for a month and he is soliciting suggestions. Here is one idea that I dreamed up just the other day as I was plodding through the hex dump of yet another freshly discovered, FourCC-chunked multimedia file format. This is the proposal– […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-331","post","type-post","status-publish","format-standard","hentry","category-open-source-multimedia"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t