[opus] Ogg Format

[Amit Ashara]

Hello Tim, Jean-Marc

Thanks for the clarification. Let me study the sample OPUS file and see if
my understanding is now clarified.

Regards
Amit

On Mon, May 9, 2016 at 2:02 PM, Timothy B. Terriberry <tterribe at xiph.org>
wrote:

> Amit Ashara wrote:
>
>> I am referring to the following file
>>
>>
>> https://en.wikipedia.org/wiki/File:Sample_of_%22Another_Day_in_Paradise%22.ogg
>>
>
> The file you are looking at is an Ogg *Vorbis* file. It's not Opus at all.
>
> The file at <
> https://people.xiph.org/~giles/2012/opus/ehren-paper_lights-96.opus>
> linked from <https://www.opus-codec.org/examples/> would be an example of
> an Ogg Opus file.
>
> I opened the file in a HEX editor. I do not see the string OpusHead in
>> the packet. It starts with Oggs. Also checking the occurrence of Oggs, I
>> see that the first packet has BOS, the next all (except last) have 00
>> (which is not defined in the RFC as continuation) and last one has EOS.
>>
>
> The header_type byte is a set of bit flags. 00 means none of them are set,
> in which case the "unset: ..." language of each flag from RFC 3533 applies.
> These pages are not continued pages.
>
> The first packet in this ogg file makes sense.
>>
>> The second packet (I am taking a part of it)
>>
>
> You mean page, not packet. They are different.
>
> 4f 67 67 53 = Oggs (THIS IS OK)
>> 00 = Version (THIS IS OK)
>> 00 = Header Type (WHY IS THIS 0)??
>>
>
> See above.
>
> 00 00 00 00 00 00 00 00 = Granule Position (THERE IS NO SPECIFIC
>> INFORMATION)
>>
>
> This is the correct value to use for header packets.
>
> 7e 46 00 00 = Bit Stream Serial Number (THIS IS OK)
>> 01 00 00 00 = Page Sequence Number (THIS IS OK)
>> 89 ab 50 5e = Checksum (THIS IS OK)
>> 10 = Page Segments is 16, so there would be 16 segments after this
>> 2d ff ff ff ff ff ff ff ff ff ff ff ff ff ff c1 = Each Segment Size (IS
>> THIS CORRECT)??
>> 03 76 6f = First 3 data from Segment 0 indicated by the size 2d (IS THIS
>> CORRECT INTERPRETATION)??
>>
>
> These are both correct.
>
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