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

[Alex Converse]

On Fri, Sep 18, 2009 at 6:42 PM, Baptiste Coudurier
<baptiste.coudurier at gmail.com> wrote:
> Hi,
>
> On 09/18/2009 03:35 PM, Thilo Borgmann wrote:
>>
>> Alex Converse schrieb:
>>>
>>> On Sun, Aug 23, 2009 at 3:51 PM, Thilo
>>> Borgmann<thilo.borgmann at googlemail.com> ?wrote:
>>>>
>>>> Revision 6 attached (rev. 5 skipped...)
>>>>
>>>> [...]
>
>>>>
>>>>
>>>> Index: libavcodec/mpeg4audio.h
>>>> ===================================================================
>>>> --- libavcodec/mpeg4audio.h ? ? (revision 19689)
>>>> +++ libavcodec/mpeg4audio.h ? ? (working copy)
>>>> @@ -36,6 +36,7 @@
>>>> ? ? int ext_sampling_index;
>>>> ? ? int ext_sample_rate;
>>>> ? ? int ext_chan_config;
>>>> + ? ?int channels;
>>>> ?} MPEG4AudioConfig;
>>>>
>>>> ?extern const int ff_mpeg4audio_sample_rates[16];
>>>> Index: libavformat/mov.c
>>>> ===================================================================
>>>> --- libavformat/mov.c ? (revision 19689)
>>>> +++ 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;
>>>> + ? ? ? ? ? ? ? ?}
>>>> ? ? ? ? ? ? ? ? if (cfg.object_type == 29&& ?cfg.sampling_index< ?3) //
>>>> old mp3on4
>>>> ? ? ? ? ? ? ? ? ? ? st->codec->sample_rate =
>>>> ff_mpa_freq_tab[cfg.sampling_index];
>>>> ? ? ? ? ? ? ? ? else
>>>
>>> The rest of this seems OK but Rob and Baptiste are the maintainers here.
>>
>
> Maybe we should always set ->channels in mpeg4audio_get_config, that would
> simplify the code everywhere else. What do you think ?

In principle that seems fine as long as it doesn't break muxing or
decoding files with (those awful) PCEs. In practice this probably
means adding yet more PCE code to mpeg4audio.[ch] since it doesn't
look like there is any way to adapt ff_copy_pce_data (mpeg4audio.c) or
decode_pce (aac.c) to this purpose.

I would also accept having this as an inevitable goal and leaving it
on a todo list for a while. This whole multichannel business in MPEG 4
audio was dreadfully thought out but there is nothing we can do about
it now.