[FFmpeg-devel] [PATCH] libmp3lame: 32 bit encoding

[Peter Belkner]

Find a revisewd patch below.

On 16.04.2011 11:22, Carl Eugen Hoyos wrote:
> Peter Belkner<pbelkner<at>  snafu.de>  writes:
>
>    
>> the patch enables libmp3lame to encode at 32 bit. This is especially
>> useful if audio is fed from SoX (http://sox.sourceforge.net/) into
>> FFmpeg because SoX works at 32 bit and hence no additional
>> re-quantization is needed.
>>      
> Does every supported lame version support 32bit encoding?
>    
 From where I know what are the supported lame versions? Are there any 
according symbols defined from config?
>    
>> +    if (AV_SAMPLE_FMT_S16 == avctx->sample_fmt) {
>> +        s->s32_data.left = NULL;
>> +        s->s32_data.right = NULL;
>>      
> This looks unneeded.
>    
I removed this assuming that the memory block priv_data is pointing to 
is zeroed out.
>    
>> +    } else {
>> +        s->s32_data.left = av_malloc(avctx->frame_size * sizeof(long));
>>      
> And I suspect this is wrong. (long has different sizes on different platforms,
> or am I wrong?)
>    

I think this is correct independent on whether "long" is 32 or 64 bits 
because these are the buffers given to lame. The following is from "lame.h":

    /* Same as lame_encode_buffer_long(), but with correct scaling.
      * !! NOTE: !! data must still be scaled to be in the same range as
      * type 'long'.   Data should be in the range:  +/- 2^(8*size(long)-1)
      *
      */
    int CDECL lame_encode_buffer_long2(
             lame_global_flags*  gfp,           /* global context
    handle         */
             const long     buffer_l [],       /* PCM data for left
    channel     */
             const long     buffer_r [],       /* PCM data for right
    channel    */
             const int           nsamples,      /* number of samples per
    channel */
             unsigned char*      mp3buf,        /* pointer to encoded
    MP3 stream */
             const int           mp3buf_size ); /* number of valid
    octets in this
                                                  
    stream                        */

Assuming lame is compiled on a system with a 64 bit long than propably I 
have to provide according buffers.

On the other hand I corrected casting the frame buffer provided by 
FFmpeg to (int32_t *).

>    
>> +        s->s32_data.right = av_malloc(avctx->frame_size * sizeof(long));
>>      
>    
>> +        if (NULL == s->s32_data.left || NULL == s->s32_data.right)
>> +            return -1;
>>      
> There is an error code for out_of_memory, please use it.
>    

Changed it to AVERROR_NOMEM.

Peter
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