[FFmpeg-devel] [PATCH] libavfilter-soc: implement pad filter

Vitor Sessak vitor1001
Sun May 31 17:09:51 CEST 2009

Michael Niedermayer wrote:
> On Sat, May 30, 2009 at 09:31:06PM +0200, Vitor Sessak wrote:
>> Michael Niedermayer wrote:
>>> On Sat, May 30, 2009 at 06:37:55PM +0200, Vitor Sessak wrote:
>>>> Michael Niedermayer wrote:
>>>>> On Sat, May 30, 2009 at 06:25:37PM +0200, Vitor Sessak wrote:
>>>>>> Michael Niedermayer wrote:
>>>>>>> On Sat, May 30, 2009 at 03:44:00PM +0200, Vitor Sessak wrote:
>>>>>>>> Michael Niedermayer wrote:
>>>>>>>>> On Fri, May 22, 2009 at 02:31:57PM +0200, Vitor Sessak wrote:
>>>>>>>>>> Stefano Sabatini wrote:
>>>>>>>>>>> On date Thursday 2009-05-21 23:20:51 +0200, Stefano Sabatini 
>>>>>>>>>>> encoded:
>>>>>>>>>>>> On date Wednesday 2009-05-20 20:42:21 +0200, Vitor Sessak 
>>>>>>>>>>>> encoded:
>>>>>>>>>>> [...]
>>>>>>>>>>>>> I suppose you didn't test the changes to ffmpeg.c, unless you 
>>>>>>>>>>>>> forgot to  attach the patch for vsrc_buffer.c. I imagine that 
>>>>>>>>>>>>> here handling  avfilter_request_frame() without memcpy'ing the 
>>>>>>>>>>>>> whole frame (as is done  in ffplay.c) would be non trivial.
>>>>>>>>>>> In attachment an updated patch with the missing changes to
>>>>>>>>>>> vsrc_buffer.c.
>>>>>>>>>>> Can someone suggest how would be possible to avoid the initial 
>>>>>>>>>>> frame
>>>>>>>>>>> -> picref memcpy?
>>>>>>>>>> What non lavfi-patched ffmpeg.c does now is:
>>>>>>>>>> 1- allocs a frame with the padding specified by command-line opts 
>>>>>>>>>> -padXXXX
>>>>>>>>>> 2- decodes the frame to this buffer. Note that this buffer might 
>>>>>>>>>> need to be reused for ME.
>>>>>>>>>> what I suggest:
>>>>>>>>>> a) For the first frame
>>>>>>>>>> 1- ffmpeg.c allocs a frame with no padding.
>>>>>>>>>> 2- libavfilter request a frame with padding px,py.
>>>>>>>>>> 3- ffmpeg.c allocs a frame with padding px, py, copies the frame to 
>>>>>>>>>> it and free the replaces (freeing) the old frame by the new
>>>>>>>>>> 4- ffmpeg.c passes the new frame to the filter framework
>>>>>>>>>> b) For the next frame
>>>>>>>>>> 5- ffmpeg.c decodes the frame with padding px, py
>>>>>>>>>> 6- libavfilter request a frame with padding px2, py2
>>>>>>>>>> 7- if (px2 > px || py2 > py) alloc another frame and memcpy the pic 
>>>>>>>>>> to it (and set px = px2; py = py2;). if not, just send the frame 
>>>>>>>>>> pointer to libavfilter
>>>>>>>>> 1 - the decoder which is pretty much a filter with no input requests
>>>>>>>>>     from the next filter a buffer.
>>>>>>>>> 1b- the next filter can pass this request up until to the video 
>>>>>>>>> output
>>>>>>>>>     device in principle or return a buffer. If this request passes a
>>>>>>>>>     "pad" filter it is modified accordingly.
>>>>>>>>> 2 - the decoder decodes into this frame.
>>>>>>>>> Which part of that are you not understanding 
>>>>>>>> I probably was missing that there is no decoder that need not only to 
>>>>>>>> preserve, but to output to the same data pointers of the last frame. 
>                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>>>>>>> Can you confirm that you can decode the first frame in a buffer and 
>>>>>>>> the second frame in a different buffer for every codec?

>>>>>>> no i cant confirm that, the filter framework must support that as well
>>>>>>> but i cant see in how far that would be a problem.

>> What do you propose? Your previous proposal choke for the case of frames 
>> that differs in padding and a codec that need the previous frame as output.
> sorry, i do not know what you talk about, you will have to explain the
> problem you hint at more verbosely

I think I didn't understand what you mentioned above. Imagine the 
following code snippet for decoding two frames

AVFrame frames[2] = {avcodec_alloc_frame(),avcodec_alloc_frame()};
AVFrame *f1 = frames[0];
AVFrame *f2;
AVPacket pkt;

av_read_frame(formatCtx, &packet);
avcodec_decode_video2(codecCtx, f1, &x, &packet);

switch(var) {
     case DO_AS_FFMPEG_C_DO:
         // This have to work, it's what ffmpeg.c do
         f2 = f1;
     case BUFFER_MEMCPY:
         // This might work even if the decoder looks for the previously
         // decoded pixels in the frame
         f2 = frames[1];
         avpicture_copy(f2, f1);
         f2 = frames[1];

av_read_frame(formatCtx, &packet);
avcodec_decode_video2(codecCtx, f2, &var, &packet);

My question is: for what values of var would this code work for every 
codec? If only DO_AS_FFMPEG_C_DO works, if the padding values increases 
even a single time, we'll have to do memcpy() for every following frame. 
If BUFFER_MEMCPY works, we'll have to do a memcpy() every time the 
padding values increases. And, finally, if BUFFER_NO_MEMCPY works, your 
solution works and there is never the need to do any memcpy'ing.


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