[asterisk-dev] Asterisk goes Spatial Conferencing: the STEAK project

[Dennis Guse]

Thanks Joshua,

just to be clear that I understood it correctly.
1. We would extend ast_format [2] with the additional field `uint
channel_count:1`
2. We would modify `opus_parse_sdp_fmtp` [1] to set
`cloned->channel_count=2`on the `ast_format` to be returned.

Would this be acceptable or is this conceptually an issue?

[1] https://github.com/asterisk/asterisk/blob/master/res/res_format_attr_opus.c#L129
[2] http://doxygen.asterisk.org/trunk/d0/d98/structast__format.html
---
Dennis Guse


On Tue, Oct 25, 2016 at 12:33 PM, Joshua Colp <jcolp at digium.com> wrote:
> Dennis Guse wrote:
>>
>> Hey,
>>
>> last week we started reworking the major patch [1] and could not solve
>> one issue.
>> At the moment, the softmix_bridge determines if interleaved stereo can
>> be written by querying ast_format's attribute data if OPUS is used ([2]):
>>
>> ```
>> struct opus_attr *attr = ast_format_get_attribute_data(format);
>> if (attr != NULL) {
>>    if (attr->stereo == 1) {
>>       *sample_rate = attr->maxplayrate;
>>       return 1;
>>    }
>> }
>> ```
>>
>> In fact, this approach is conceptually flawed as it introduces a direct
>> dependency between softmix_bridge and opus.
>> To remove this dependency, we tried to attach this information to
>> ast_codec (channel_count uint; default 1), but did not find a useful and
>> working method to write the newly introduced field.
>> We tried to set it in the res/res_format_attr_opus, ie, while parsing
>> the fmtp for OPUS.
>> Here, the ast_codec is const and we thus cannot be change.
>>
>> Any suggestions?
>> Are we approaching the issue from a "correct" perspective?
>
>
> The structure that is actually editable is the format (despite it being
> const in the format attribute module - this was done because it was never
> envisioned that a format attribute module would set anything directly on the
> format), this data would need to be there. The codec structure is an
> immutable structure which is shared by EVERY instance of a format that uses
> the codec. That is why you can't edit it.
>
>
> --
> Joshua Colp
> Digium, Inc. | Senior Software Developer
> 445 Jan Davis Drive NW - Huntsville, AL 35806 - US
> Check us out at: www.digium.com & www.asterisk.org
>
>
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