[ogg-dev] How to concatenate Ogg in the browser JS?

[Vitaly Zdanevich]

One more question please, just to check - in documentation I read that I must calculate CRC32 of full page (with CRC fields filled by zeroes), in xxd I see that first "page" (data before the next OggS 4f 67 67 53) is small, example here:
00000000: 4f67 6753 0002 0000 0000 0000 0000 1111  OggS............
00000010: 1111 0000 0000 34bf f18b 011e 0176 6f72  ......4......vor
00000020: 6269 7300 0000 0001 2256 0000 0000 0000  bis....."V......
00000030: 058a 0000 0000 0000 a901 4f67 6753 0000  ..........OggS..
Am I right that here I will calculate from first byte position to bytes a901 including - but not including the next OggS?


23.11.2018, 15:55, "Vitaly Zdanevich" <zdanevich.vitaly at ya.ru>:
> I found how to build CRC32 table for Ogg in JS, if anyone interested:
>
> function _makeCRC32Table() {
>     // From https://stackoverflow.com/questions/53438815/hot-to-build-crc32-table-for-ogg
>     const polynomial = 79764919;
>     const mask = 2147483648;
>     const CRCTable = new Uint32Array(256);
>     for (let i = 256; i--;) {
>         let char = i << 24;
>         for (let j = 8; j--;) {
>             char = char & mask ? polynomial ^ char << 1 : char << 1;
>         }
>         CRCTable[i] = char;
>     }
>     return CRCTable;
> }
>
> 22.11.2018, 17:43, "Vitaly Zdanevich" <zdanevich.vitaly at ya.ru>:
>>  I faced with problem about CRC32 calculation, I see that lookup table is different here https://github.com/rillian/rogg/blob/master/rogg.c#L196
>>  end for example here
>>  https://stackoverflow.com/a/18639975/1879101 - JS code on this page for building the table produces the same result. I think that generating the table is better than having hardcoded one - for security against the case when somebody accidentally change one character and this table will continue to work in 99% of cases. My current JS code for building table:
>>
>>  function _makeCRCTable() {
>>      const CRCTable = new Uint32Array(256);
>>      for (let i = 256; i--;) {
>>          let char = i;
>>          for (let j = 8; j--;) {
>>              char = char & 1 ? 3988292384 ^ char >>> 1 : char >>> 1;
>>          }
>>          CRCTable[i] = char;
>>      }
>>      return CRCTable;
>>  }
>>
>>  I need to fix something here?
>>
>>  16.11.2018, 17:57, "Timothy B. Terriberry" <tterribe at xiph.org>:
>>>   Please see the documentation: https://xiph.org/ogg/doc/framing.html
>>>
>>>   I would encourage you to use random serial numbers, as intended, also,
>>>   as any downstream consumers of your files will face limitations similar
>>>   to the ones you are facing if they want to do anything more with them.
>>>
>>>   But before you go too far down the route of changing the serial numbers,
>>>   can you tell us what software is producing Oggs with a hard-coded serial
>>>   number to begin with?
>>>
>>>   Vitaly Zdanevich wrote:
>>>>    Thank you again for your help, now I am thinking about much simpler solution - because all my Oggs comes from the the one source looks like I can alter serial and crc32 at their hardcoded positions. Please see this screenshot https://giphy.com/gifs/9AIe7ksYBwiYQoLVv9/fullscreen with serials 11111111 and 22222222- it will be correct approach? And can you please say me from what region I need to calculate crc32? And also as we can see on the screenshot above - changed two groups of numbers beside the serials - what is that? Thank you very much for help.
>>>>
>>>>    16.11.2018, 04:01, "Ralph Giles" <giles at thaumas.net>:
>>>>>    On 2018-11-15 11:01 a.m., Vitaly Zdanevich wrote:
>>>>>>      Maybe you know some existing code snippet or library for Javascript for altering serial and crc?
>>>>>
>>>>>    I don't, sorry.
>>>>>
>>>>>>      Just now I compiled your quick script to wasm but the size is 28K, > I think about simple correct solution for that case.
>>>>>
>>>>>    If you strip out the fprintf()s for progress and error reporting, it
>>>>>    might get smaller. More so if you replace the open/memmap step with
>>>>>    direct access to the blob as an array. But it's not very much code to
>>>>>    just port the functions to pure js.
>>>>>
>>>>>       -r
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