[Libav-user] How to Convert AV_PIX_FMT_RGB24 to AV_PIX_FMT_YUV420P

[Chris Share]

Thanks for the sample code.

I have a couple of further questions:

1. If the input data is in a vector of unsigned chars (RGBRGB...), what is the best pixel format to use?

2. The input data is represented by the following method parameter: void* ptInData - I'm not clear as to how the vector is converted to an appropriate type - should it be an array of chars (RGBRGB...) or does the data need to be arranged differently (RRR...GGG...BBB...)?

Cheers,

Chris

________________________________
From: Hector Alonso <halonso at vpod.tv>
To: "This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter." <libav-user at ffmpeg.org> 
Sent: Thursday, 14 February 2013 8:38 PM
Subject: Re: [Libav-user] How to Convert AV_PIX_FMT_RGB24 to AV_PIX_FMT_YUV420P


Hi Chris,

You can implement some kind of function like:

// dependencies into C++ 
extern"C"{
#include<libavformat/avformat.h>
#include<libswscale/swscale.h>
#include<libavutil/pixdesc.h>
#include<libavutil/samplefmt.h>
#include<libavutil/intreadwrite.h>
}

/**
*Thisfunctionconvertsanimage(uncompressedbuffer)fromaninput
*specifiedpixelformattoanoutputspecifiedpixelformatandbuffer.
*dependenciesLibAV.
*@param[in]eInFormatinputimagePixelformat at seeLibaAVPixelFormatenumtype.
*@param[in]iInWidthinputimagewidth
*@param[in]iInHeightinputimageheight
*@param[in]ptInDatainputimagebuffer
*@param[in]eOutFormatoutputimagePixelformat at seeLibaAVPixelFormatenumtype.
*@param[in]iOutWidthoutputimagewidth
*@param[in]iOutHeightoutputimageheight
*@param[out]srcoutputimagebuffer
*@returntrueifeverythingwascorrect,falseotherwise)
**/
boolConvertImage1(PixelFormateInFormat,intiInWidth,intiInHeight,void*ptInData,PixelFormateOutFormat,intiOutWidth,intiOutHeight,AVPicture*src)
{
SwsContext*ptImgConvertCtx;// Frame conversion context

AVPictureptPictureIn;
uint8_t*ptBufferIn;

//Initialize convert context
//------------------
ptImgConvertCtx=sws_getContext(iInWidth,iInHeight,eInFormat,// (source format)
iOutWidth,iOutHeight,eOutFormat,// (dest format)
SWS_BICUBIC,NULL,NULL,NULL);

// Init input frame:
//------------------
// Allocate an AVFrame structure


// Determine required buffer size and allocate buffer
// int iNumBytesIn=avpicture_get_size(eInFormat, iInWidth,iInHeight);

ptBufferIn=(uint8_t*)(ptInData);

// Assign appropriate parts of buffer to image planes in pFrameOut
avpicture_fill(&ptPictureIn,ptBufferIn,eInFormat,iInWidth,iInHeight);

// Do conversion:
//------------------
intiRes=sws_scale(ptImgConvertCtx,
ptPictureIn.data,//src
ptPictureIn.linesize,
0,
iInHeight,
src->data,//dst
src->linesize);


//Free memory
sws_freeContext(ptImgConvertCtx);

//Check result:
if(iRes==iOutHeight)
returntrue;

returnfalse;
}

And use it like this (in this example is used to downscale, but you can use it for rescaling and or pixel format conversions)

// Downscale
AVPicturesrc;
intiWidth=m_ptCurrentVideoMode->getWidth()/DL_LOW_DEFINITION_DEN;
intiHeight=(m_ptCurrentVideoMode->getHeight()*iWidth)/m_ptCurrentVideoMode->getWidth();
iWidth=(floor(iWidth/2))*2;
iHeight=(floor(iHeight/2))*2;

avpicture_alloc(&src,AV_PIX_FMT_UYVY422,iWidth,iHeight);

if(!ConvertImage1(AV_PIX_FMT_UYVY422,
m_ptCurrentVideoMode->getWidth(),
m_ptCurrentVideoMode->getHeight(),
(void*)ptBuffer,
AV_PIX_FMT_UYVY422,
iWidth,iHeight,
&src))
{
avpicture_free(&src);
return;
}

// ... whatever ...

// Free aux frame
avpicture_free(&src);
I hope it helps!


On Thu, Feb 14, 2013 at 10:00 AM, Chris Share <cpsmusic at yahoo.com> wrote:

Hi,
>
>I'm currently trying to implement file export for the open source animation program Pencil2D. This involves converting RGB (0 - 255) image data to a suitable movie format.
>
>The examples in the source tree have been very helpful however I still have some questions:
>
>The scaling_video.c is close to what I need however the conversion is the opposite of what I want. What I'm not clear about is how to change the "fill_yuv_image" function to something like "fill_rgb_image". How does the RGB data get written into the "uint8_t *data[4]"? Is it written consecutively (all R values get written to data[0], all G values to data[1], etc.)?
>
>Cheers,
>
>Chris
>_______________________________________________
>Libav-user mailing list
>Libav-user at ffmpeg.org
>http://ffmpeg.org/mailman/listinfo/libav-user
>

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