[Libav-user] Help with unpacking PIX_FMT_YUV4* data types

[J Decker]

During Init.....


file->pVideoFrameRGB = ffmpeg.av_frame_alloc();
{
int num_bytes;
#ifdef WIN32
#define PIX_FMT  PIX_FMT_BGRA
#else
#define PIX_FMT  PIX_FMT_RGBA
#endif
num_bytes = ffmpeg.avpicture_get_size(PIX_FMT, file->pVideoCodecCtx->width,
file->pVideoCodecCtx->height);
file->rgb_buffer = (_8 *)ffmpeg.av_malloc(num_bytes*sizeof(uint8_t));
ffmpeg.avpicture_fill((AVPicture*)file->pVideoFrameRGB, file->rgb_buffer,
PIX_FMT
, file->pVideoCodecCtx->width, file->pVideoCodecCtx->height);
}
file->img_convert_ctx = ffmpeg.sws_getContext(file->pVideoCodecCtx->width,
file->pVideoCodecCtx->height
, file->pVideoCodecCtx->pix_fmt
, file->pVideoCodecCtx->width, file->pVideoCodecCtx->height
, PIX_FMT, SWS_BICUBIC, NULL, NULL, NULL);



// CDATA is _32 color data in my library, image surface is the raw out RGB

CDATA *surface = GetImageSurface( out_surface );
ffmpeg.sws_scale(file->img_convert_ctx
, (const uint8_t*const*)file->pVideoFrame->data, file->pVideoFrame->linesize
, 0, file->pVideoCodecCtx->height
, file->pVideoFrameRGB->data
, file->pVideoFrameRGB->linesize);

// depending on target platform, the image needs to be 'flipped' on output
from the pVideoFrameRGB
{
#ifdef _INVERT_IMAGE
int row;
for( row = 0; row < file->pVideoFrame->height; row++ )
{
memcpy( surface + ( file->pVideoFrame->height - row - 1 ) *
file->pVideoFrame->width
, file->rgb_buffer + row * sizeof(CDATA) * file->pVideoFrame->width,
file->pVideoFrame->width * sizeof( CDATA ) );
}
#else
memcpy( surface
, file->rgb_buffer , file->pVideoFrame->height * file->pVideoFrame->width *
sizeof( CDATA ) );
#endif
}


// Output surface to display


On Mon, Mar 10, 2014 at 6:11 PM, Ricky Huang <rhuang.work at gmail.com> wrote:

>
> On Mar 10, 2014, at 4:28 PM, J Decker <d3ck0r at gmail.com> wrote:
>
> I would think you would just use 'sws_getContext' and 'sws_scale'
> worked good for me...
>
>
> Thank you for the pointer.  May I have a little more info regarding how
> you used sws_getContext()? I found its API definition as follows:
>
> struct SwsContext *  sws_getContext (int srcW, int srcH,
> enum PixelFormat srcFormat, int dstW, int dstH, enum PixelFormat dstFormat,
> int flags, SwsFilter *srcFilter, SwsFilter *dstFilter, const double *param)
>
> and it allocates and returns a struct SwsContext*.
>
> In my case I am not modifying anything in my filter, why is this function
> good for me? (I am assuming this performs some kind of transformation
> because there's a source and destination).  Also in the returned SwsContext
> struct, I see there are 4 members:
>
> int  lumXInc
> int  chrXInc
> int  lumYInc
> int  chrYInc
>
> perhaps this is where I can get the luminance?  In that case, does it mean
> I have to perform some kind of transformation before even able to get the
> Context?
>
>
> Thank you for in advance for clarification.
>
>
>
> On Mon, Mar 10, 2014 at 4:18 PM, Ricky Huang <rhuang.work at gmail.com>wrote:
>
>> Hello all,
>>
>> I am writing code that extracts the luminance component of an input video
>> using my own custom filter in libavfilter - specifically I am extracting it
>> from "PIX_FMT_YUV420P" a video and I am wondering how to go about doing so.
>>  According to the pixfmt.h header:
>>
>>
>> PIX_FMT_YUV420P,   ///< planar YUV 4:2:0, 12bpp, (1 Cr & Cb sample per
>> 2x2 Y samples)
>>
>>
>> I am not sure how to interpret that.  Assuming I am doing this in my
>> draw_slice() function. It has the definition of:
>>
>>
>> static void draw_slice(AVFilterLink *inlink, int y0, int h, int slice_dir)
>>
>>
>> I know I can get to the input data plane by:
>>
>>
>> AVFilterBufferRef *cur_pic = link->cur_buf;
>> uint8_t *data = cur_pic->data[0];
>>
>>
>> But there are multiple "planes" in the data.  Does data[0], data[1],
>> data[2] correspond to each of the Y, U, V channels?
>>
>> Also, once I am able to point my pointer at the correct coordinate, how
>> should I interpret the extracted result (float, int, etc)?
>>
>>
>> Thank you in advance.
>>
>> _______________________________________________
>> Libav-user mailing list
>> Libav-user at ffmpeg.org
>> http://ffmpeg.org/mailman/listinfo/libav-user
>>
>>
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