[FFmpeg-devel] [PATCH] allow high audio sample rates in mov/mp4 muxer

Baptiste Coudurier baptiste.coudurier
Mon Sep 6 21:43:24 CEST 2010

Hi guys,

On 9/6/10 11:41 AM, Justin Ruggles wrote:
> Alex Converse wrote:
>> On Sun, Jun 13, 2010 at 9:16 PM, Justin Ruggles
>> <justin.ruggles at gmail.com>  wrote:
>>> Michael Niedermayer wrote:
>>>> On Sun, Jun 13, 2010 at 12:52:29PM -0400, Justin Ruggles wrote:
>>>>> Baptiste Coudurier wrote:
>>>>>> On 6/12/10 8:26 AM, Justin Ruggles wrote:
>>>>>>> Baptiste Coudurier wrote:
>>>>>>>> On 06/10/2010 01:27 PM, Justin Ruggles wrote:
>>>>>>>>> Alex Converse wrote:
>>>>>>>>>> On Thu, Jun 10, 2010 at 1:54 PM, Justin Ruggles
>>>>>>>>>> <justin.ruggles at gmail.com>    wrote:
>>>>>>>>>>> Hi,
>>>>>>>>>>> This patch allows the use of sample rates>    65535 in mov/mp4 (e.g. 96kHz
>>>>>>>>>>> and 192kHz).  I don't know where to find this info in the MP4 spec, but
>>>>>>>>>>> this is how the MPEG-4 ALS Reference Software does it.
>>>>>>>>>> It might also be a good idea to look at the AAC 88.2/96 kHz test vectors.
>>>>>>>>> Well, it seems that it shouldn't be 0, but should be the actual sample
>>>>>>>>> rate using more than 16 bits.  I guess the reserved value that follows
>>>>>>>>> is no longer reserved.  I'll send a new patch soon.
>>>>>>>> Humm, I don't feel confident about this.
>>>>>>>> Can we ask ISO about this ?
>>>>>>> Ok, so after some more research, it looks like the reference samples and
>>>>>>> the specs are in agreement that the sample rate field is 16.16 fixed
>>>>>>> point and that only the low 16 bits of the sample rate are written.
>>>>>> Can you please quote the specs ? Just for reference.
>>>>> ISO 14496-12 3rd Ed. 2008
>>>>>  Sample Description Box, Semantics
>>>>> SampleRate is the sampling rate expressed as a 16.16 fixed-point number
>>>>> (hi.lo)
>>>> Numbers 0.0 - 65535.65535 can be expressed as 16.16 fixed point.
>>>> Numbers outside this range cannot be expressed as fixed point unless you
>>>> define one of the used concepts like "expressed" differently from common
>>>> sense.
>>>> Thus it follows that in ISO 14496-12 3rd Ed. 2008 the existence of a
>>>> Sample Description Box in a file is incompatible with sampling rates
>>>> beyond 65535.65535.
>>>> Of course this conclusion can only be drawn if we take the quoted text
>>>> litterally and assume the spec is written by a person who used exact
>>>> language.
>>>> I tend toward asking ISO as well and also to point out that the spec is
>>>> unclear either way.
>>> The spec is certainly unclear and some ISO references differ:
>>> - The reference samples for 96kHz AAC write a value of 30464.0000, which
>>> is the low 16 bits of 96000.
>> I'm seeing 0 for al0[0-2]_96.mp4.
>> http://streams.videolan.org/Mpeg_Conformance/ftp.iis.fhg.de/mpeg4audio-conformance/compressedMp4/al00_44.mp4
> Maybe I was looking at older test vectors?  I'm not sure, but the AAC
> reference samples you pointed to do all have 0, which corresponds to the
> most recent ALS reference samples.  New patch attached.  Same as
> original patch but smaller.

Again, this looks hackish, and I'd really like ISO point on this.

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