[FFmpeg-devel] [PATCH] code to parse mpeg4audio extradata

[Baptiste Coudurier]

Hi,

Michael Niedermayer wrote:
> On Mon, Mar 31, 2008 at 12:41:08AM +0200, Baptiste Coudurier wrote:
>> Hi,
>>
>> Michael Niedermayer wrote:
>>> On Wed, Mar 19, 2008 at 04:54:03PM +0100, Baptiste Coudurier wrote:
>>>> Hi,
>>>>
>>>> Here is a patch that adds parsing of mpeg4audio extradata, and retrieve
>>>> needed infos for decoders (only mp3on4 atm, but will be needed for aac),
>>>> and will be used by mov demuxer ideally to correctly compute sample rate
>>>> and channels.
>>>> Also extract common mpeg4audio code from aac_parser.c.
>>> [...]
>>>
>>>> Index: libavcodec/mpegaudiodec.c
>>>> ===================================================================
>>>> --- libavcodec/mpegaudiodec.c	(revision 12503)
>>>> +++ libavcodec/mpegaudiodec.c	(working copy)
>>>> @@ -2486,9 +2486,11 @@
>>>>  #endif /* CONFIG_MP3ADU_DECODER */
>>>>  
>>>>  #ifdef CONFIG_MP3ON4_DECODER
>>>> +
>>>> +#include "mpeg4audio.h"
>>>> +
>>>>  /* Next 3 arrays are indexed by channel config number (passed via codecdata) */
>>>> -static int mp3Frames[16] = {0,1,1,2,3,3,4,5,2};   /* number of mp3 decoder instances */
>>>> -static int mp3Channels[16] = {0,1,2,3,4,5,6,8,4}; /* total output channels */
>>>> +static const uint8_t mp3_frames[8] = {0,1,1,2,3,3,4,5}; /* number of mp3 decoder instances */
>>> seperate commit and why does the 2 at the end disapear?
>>>
>> Yes, of course. I'll post an updated patch for mp3on4 decoder anyway.
>>
>> It disappears because this last configuration is not mentioned anymore
>> in published specs. It was in old draft, and I expect/hope nobody ever
>> used it.
>>
>>> [...]
>>>
>>  > This either needs a function ptr as a argument for parsing codec
>> specific stuff
>>> or return some ptr / bitindex to where that is stored. Later is more flexible
>>> for example with a binary decoder which expects a pointer to this stuff.
>>>
>> I like the idea of bitindex. Updated patch attached.
> 
> [...]
>> +    if (c->ext_object_type != 5) {
>> +        int bits_left = buf_size*8 - specific_config_bitindex;
>> +        for (; bits_left > 15; bits_left--) {
>> +            if (show_bits(&gb, 11) == 0x2b7) { // sync extension
>> +                get_bits(&gb, 11);
> 
>> +                if ((c->ext_object_type = get_bits(&gb, 5)) == 31)
>> +                    c->ext_object_type = 32 + get_bits(&gb, 6);
> 
> That code occurs 3 times, maybe it would be more readable in a fuction.
> The same is true for the sample_rate code below.
> 
>> +                if (c->ext_object_type == 5)
>> +                    if ((c->sbr = get_bits1(&gb)) == 1) {
>> +                        if ((c->ext_sampling_index = get_bits(&gb, 4)) == 0x0f)
>> +                            c->ext_sample_rate = get_bits(&gb, 24);
>> +                        else
>> +                            c->ext_sample_rate = ff_mpeg4audio_sample_rates[c->ext_sampling_index];
>> +                    }
> 
> [...]
>> +typedef struct {
>> +    int object_type;
>> +    int sampling_index;
> 
> Is the *sampling_index really needed? Iam asking because it would complicate
> a factored out function to read the sample_rate.
> 

You're right, I factored out, updated patch attached.

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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