[FFmpeg-devel] [PATCH] Parsing ALS object type in MPEG-4

[Baptiste Coudurier]

On 11/10/2009 02:06 PM, Alex Converse wrote:
> On Tue, Nov 10, 2009 at 4:29 PM, Baptiste Coudurier
> <baptiste.coudurier at gmail.com>  wrote:
>>
>> On 11/10/2009 12:10 PM, Thilo Borgmann wrote:
>>>
>>> Baptiste Coudurier schrieb:
>>>>
>>>> On 10/11/2009 03:04 AM, Thilo Borgmann wrote:
>>>>>
>>>>> Baptiste Coudurier schrieb:
>>>>>>
>>>>>> On 10/9/09 1:48 PM, Alex Converse wrote:
>>>>>>>
>>>>>>> On Sun, Aug 23, 2009 at 3:51 PM, Thilo Borgmann
>>>>>>> <thilo.borgmann at googlemail.com>      wrote:
>>>>>>>>
> [...]
>>>>> Index: libavformat/mov.c
>>>>> ===================================================================
>>>>> --- libavformat/mov.c    (revision 20011)
>>>>> +++ libavformat/mov.c    (working copy)
>>>>> @@ -434,9 +434,13 @@
>>>>>                    MPEG4AudioConfig cfg;
>>>>>                    ff_mpeg4audio_get_config(&cfg, st->codec->extradata,
>>>>>                                             st->codec->extradata_size);
>>>>> +                if (cfg.chan_config) {
>>>>>                    if (cfg.chan_config>     7)
>>>>>                        return -1;
>>>>>                    st->codec->channels =
>>>>> ff_mpeg4audio_channels[cfg.chan_config];
>>>>> +                } else {
>>>>> +                    st->codec->channels = cfg.channels;
>>>>> +                }
>>>>
>>>> By always setting cfg.channels I wanted to avoid the
>>>> if (cfg.chan_config) ...
>>>>
>>>> That's ok though.
>>>>
>>>
>>> Hm I tried to but cannot really follow the arguing about setting
>>> cfg.channels. Do you mean to always set
>>>
>>> st->codec->channels = cfg.channels;
>>>
>>> ? This would set it to 0 (for PCE streams == !ALS) but don't we loose
>>> something from ff_mpeg4audio_channes[] in that case? And are PCE streams
>>> always given if ALS is not given?
>>
>> What do we loose ? It seems that chan_config value is still set, and it avoids duplicating this if everywhere.
>
> Has it been confirmed that this doesn't break any of the ways that AAC
> or MP4A can be muxed into mov-realted formats that we support?

Why would it be ?

> Particularly:
> MP4 objectTypeIndication 0x66/0x67

0x68 as well ?
Currently, CODEC_ID_AAC will always use 0x40.
MPEG2 AAC might needs a different CODEC_ID value.

> MP4 objectTypeIndication 0x40 AOT_LC channel_config = 0
> MP4 objectTypeIndication 0x40 AOT_LC channel_config>  0
> MP4 objectTypeIndication 0x40 AOT_L1/L2/L3
> MP4 objectTypeIndication 0x40 AOT_PS (Old mp3on4)
> AAC in mov?

I don't understand what you mean.
Do you mean that chan_config is used when muxing ?
chan_config is located in extradata is supplied by the encoder or is 
kept when stream copying. The muxer only set mp4 object type id based on 
codec, and uses 0x40 for CODEC_ID_AAC.

Currently channels are set according to chan_config using 
ff_mpeg4audio_channels[], if chan_config is 0 channels are set to 0, and 
decoders will init channels parsing pce or anything else.

-- 
Baptiste COUDURIER
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