[Ffmpeg-devel] Re: [PATCH] demuxer for dcinema audio

Baptiste Coudurier baptiste.coudurier
Wed Aug 30 18:41:36 CEST 2006


Michael Niedermayer wrote:
> Hi
> On Wed, Aug 31, 2005 at 09:54:19AM +0200, Reimar D?ffinger wrote:
>> Hi,
>> On Wed, Aug 31, 2005 at 03:33:13AM +0200, Michael Niedermayer wrote:
>>> On Sat, Aug 27, 2005 at 05:08:38PM +0200, Reimar D?ffinger wrote:
>>>> I'd like to suggest the attached patch for demuxing D-Cinema audio. It's
>>>> not exactly beautiful since it does something like decoding (changing
>>>> the bit order), but I though it to be the easier solution over adding a
>>>> special decoder (since it isn't used anywhere else).
>>>> The smil file that came with it said it was of the format "audio/302m",
>>>> and I assume it is SMPTE 302M uncompressed audio, but I don't have the
>>>> specs.
>>>> Please tell me what you think about it...
>>> uhm, well, messy ... too messy, and we have enough messy code aleady ...
>> Hmm... what would be an acceptable solution? Just moving the 24bit weird
>> audio -> "normal" 32bit audio conversion to libavcodec/pcm.c?
>> I would then have to "invent" a new format ID for MPlayer though.
>> Or which part of it is messy?
> everything, you dont even know if its SMPTE 302M, its just a guess from
> "302M" or did i miss something?
> further note, the title of 302M is 
> "Television- Mapping of AES3 Data into MPEG-2 Transport Stream"
> so its supposed to be in a MPEG-TS, how can your proposed "convert it 
> to 32bit" demuxer ever work with that?
> also note, AES3 specs can be downloaded freely from 
> http://www.aes.org/publications/standards/
> [...]

OK Im one year late.

I actually got a TS containing 302M audio and indeed the sample Reimar
refers to is the PES stream extracted from a TS. That file is 20 bit per
sample AES3 stream, containing LPCM.

Then I think it would be better to rename daud.c to s302m.c (or aes3.c)
That file could contain some functions needed to extract sample from
bitstream AVBitStreamFilter ?, and codec/sample rate/bits per sample infos.

Im trying to implement an AES3 stream parser/filter for my ts file and
my mxf files containing AES3. I guess AVBitstreamFilter is the best
option, how could it be automatically activated when I detect such a
stream ?

Samples in AES are LSB first, maybe PCM_S24DAUD should be renamed to
PCM_S20LSBF ? What do you guys think ?

Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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