[FFmpeg-devel] [PATCH 2/2] MxPEG decoder

[Anatoly Nenashev]

On 17.11.2010 16:49, Michael Niedermayer wrote:
> On Mon, Nov 15, 2010 at 03:27:07AM +0300, Anatoly Nenashev wrote:
>    
>> On 13.11.2010 04:24, Michael Niedermayer wrote:
>>      
>>> On Thu, Nov 11, 2010 at 02:16:27AM +0300, Anatoly Nenashev wrote:
>>>
>>>        
>>>> On 10.11.2010 18:28, Michael Niedermayer wrote:
>>>>
>>>>          
>>>>> On Wed, Nov 10, 2010 at 06:08:47PM +0300, Anatoly Nenashev wrote:
>>>>>
>>>>>
>>>>>            
>>>>>> [...]
>>>>>> If to read more than 16 byte at once then it is required additional
>>>>>> operations of memcpy and memmove.
>>>>>> For example. If I read buffer of 256 bytes in which audio packet
>>>>>> available in position 10 and size 100 then I need
>>>>>> to copy data of size 100-10=90 in new audio packet and move data of size
>>>>>> 256-100=156 in internal buffer. I think this may reduce the performance.
>>>>>>
>>>>>>
>>>>>>              
>>>>> you dont need to move it.
>>>>>
>>>>> and the overhead of all your code executed once every 16 bytes will reduce
>>>>> performance more than an occasional memcpy(). That said it can be done
>>>>> without memcpy by accessing the internal buffer but iam not suggesting this
>>>>> to be done.
>>>>>
>>>>>
>>>>>            
>>> There are many ways to implement this, one simple one is
>>> you have a internal buffer
>>> you read into it
>>> you return AVPackets that point into this buffer and have destruct=NULL
>>>
>>>
>>>        
>> Implemented this way.
>>
>>      
> [...]
>
>> +static int mxg_read_header(AVFormatContext *s, AVFormatParameters *ap)
>> +{
>> +    AVStream *video_st = 0, *audio_st = 0;
>>      
> the =0 is useless
>
>
>    
Ok. Removed.

> [...]
>    
>
>> +                    ret = mxg_reallocate_buffer(mxg, size + FF_INPUT_BUFFER_PADDING_SIZE);
>> +                    if (ret<  0)
>> +                        return ret;
>> +                    startmarker_ptr = mxg->buffer_ptr - 2;
>> +
>> +                    ret = get_buffer(s->pb, mxg->buffer_ptr + mxg->cache_size,
>> +                                     size - mxg->cache_size);
>> +                    if (ret<  0)
>> +                        return ret;
>>      
> i think the get_buffer() could also be moved into mxg_reallocate_buffer() and
> it be renamed accordingly. That should simplify the code
>
>    

Reimplemented.
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