[vlc-devel] [PATCH] avcodec: reconstruct the ALAC atom if we have enough data

[Steve Lhomme]

On Fri, Feb 12, 2016 at 5:53 PM, Tristan Matthews <tmatth at videolan.org> wrote:
> Hi,
>
> On Fri, Feb 12, 2016 at 10:28 AM, Steve Lhomme <robux4 at videolabs.io> wrote:
>> fixes #16620
>> ---
>>  modules/codec/avcodec/audio.c | 37 ++++++++++++++++++++++++++++++-------
>>  1 file changed, 30 insertions(+), 7 deletions(-)
>>
>> diff --git a/modules/codec/avcodec/audio.c b/modules/codec/avcodec/audio.c
>> index 159dbf1..9ce190f 100644
>> --- a/modules/codec/avcodec/audio.c
>> +++ b/modules/codec/avcodec/audio.c
>> @@ -85,15 +85,38 @@ static void InitDecoderConfig( decoder_t *p_dec, AVCodecContext *p_context )
>>          if( p_dec->fmt_in.i_codec == VLC_CODEC_ALAC )
>>          {
>>              static const uint8_t p_pattern[] = { 0, 0, 0, 36, 'a', 'l', 'a', 'c' };
>
> Maybe define 36 somewhere, or use p_pattern[3].

I'll use GetDWBE(), it's even cleaner.

>> -            /* Find alac atom XXX it is a bit ugly */
>> -            for( i_offset = 0; i_offset < i_size - (int)sizeof(p_pattern); i_offset++ )
>> +            if( i_size >= 24 && i_size < 36)
>>              {
>> -                if( !memcmp( &p_src[i_offset], p_pattern, sizeof(p_pattern) ) )
>> -                    break;
>> -            }
>> -            i_size = __MIN( p_dec->fmt_in.i_extra - i_offset, 36 );
>> -            if( i_size < 36 )
>> +                p_context->extradata =
>> +                    av_malloc( 12 + i_size + FF_INPUT_BUFFER_PADDING_SIZE );
>> +                if( p_context->extradata )
>
> What if av_malloc fails?

The same as before the extra data is empty and decoding will be
refused by avcodec.

>> +                {
>> +                    uint8_t *p_dst = p_context->extradata;
>> +
>> +                    i_size = 0;
>> +                    memcpy( &p_dst[i_size], &p_pattern[0], 8 );
>> +                    i_size += 8;
>> +                    memset( &p_dst[i_size], 0, 4 );
>> +                    i_size += 4;
>> +                    memcpy( &p_dst[i_size], &p_src[0], p_dec->fmt_in.i_extra );
>> +                    i_size += p_dec->fmt_in.i_extra;
>> +                    p_context->extradata_size = i_size;
>> +                    memset( &p_dst[i_size], 0, FF_INPUT_BUFFER_PADDING_SIZE );
>> +                }
>>                  i_size = 0;
>> +            }
>> +            else
>> +            {
>> +                /* Find alac atom XXX it is a bit ugly */
>> +                for( i_offset = 0; i_offset < i_size - (int)sizeof(p_pattern); i_offset++ )
>> +                {
>> +                    if( !memcmp( &p_src[i_offset], p_pattern, sizeof(p_pattern) ) )
>> +                        break;
>> +                }
>> +                i_size = __MIN( p_dec->fmt_in.i_extra - i_offset, 36 );
>> +                if( i_size < 36 )
>> +                    i_size = 0;
>> +            }
>>          }
>>
>>          if( i_size > 0 )
>> --
>> 2.7.0
>>
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