ffmpeg - YUV to RGB by Shader on iPhone

Question

Currently I am developing a video player using FFMPEG. I'm trying to convert YUV420P to RGB by Shader to reduce performance hit and I could see it works fine. The problem is caused when I try to change image size.

Case 1. YUV to RGB is perfect. but the image is not exactly fit to Texture Bounds. For example, if i play 640x360 video, right (640-512) part is cropped and bottom (512-360) is filled with green colored rectangle.

FRAME_X=512; //This is texture size
FRAME_Y=512;

    avpicture_fill((AVPicture *) f, [currentVideoBuffer.data mutableBytes],
               enc->pix_fmt,
               FRAME_X, FRAME_Y);

    av_picture_copy((AVPicture *) f, (AVPicture *) avFrame,
                enc->pix_fmt,
                enc->width, enc->height);

....

int yuvWidth= FRAME_X ;
int  yuvHeight= FRAME_Y;
glBindTexture ( GL_TEXTURE_2D, textureIdY );
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, 
yuvWidth, yuvHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, y_channel);


glBindTexture ( GL_TEXTURE_2D, textureIdU );
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE,
yuvWidth/2, yuvHeight/2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, u_channel);

glBindTexture ( GL_TEXTURE_2D, textureIdV );
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, 
yuvWidth/2, yuvHeight/2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, v_channel);

Case 2. If i set actual image size to texture size, then image is exactly fit to texture but the color of image is a little bit strange. It has too much green color.

Does anybody give me some clues for this?? Thanks in advance.

score 4 · Accepted Answer

首先，您需要为非幂的两个纹理设置正确的包裹模式。

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

然后，尝试将过滤模式设置为 GL_LINEAR

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

和着色器。

顶点着色器

attribute vec4 position;  
attribute vec2 texcoord;  
uniform mat4 modelViewProjectionMatrix;  
varying vec2 v_texcoord;

void main()  
{  
  gl_Position = modelViewProjectionMatrix * position;  
  v_texcoord = texcoord.xy;  
}

设置顶点

vertices[0] = -1.0f;  // x0
vertices[1] = -1.0f;  // y0
vertices[2] =  1.0f;  // ..
vertices[3] = -1.0f;
vertices[4] = -1.0f;
vertices[5] =  1.0f;
vertices[6] =  1.0f;  // x3
vertices[7] =  1.0f;  // y3

为 2d 图像（精灵）加载适当的 viewProj 矩阵，最好使用正射投影。

GLfloat modelviewProj[16];  
mat4f_LoadOrtho(-1.0f, 1.0f, -1.0f, 1.0f, -1.0f, 1.0f, modelviewProj);  
glUniformMatrix4fv(_uniformMatrix, 1, GL_FALSE, modelviewProj);

接下来，确保使用正确的文本坐标，像这样

GLfloat texCoords[] = {  
  0.0f, 1.0f,  
  1.0f, 1.0f,  
  0.0f, 0.0f,  
  1.0f, 0.0f,  
};

最后，像这样的片段着色器：

varying highp vec2 v_texcoord;  
uniform sampler2D s_texture_y;  
uniform sampler2D s_texture_u;  
uniform sampler2D s_texture_v;

void main()  
{  
  highp float y = texture2D(s_texture_y, v_texcoord).r;  
  highp float u = texture2D(s_texture_u, v_texcoord).r - 0.5;  
  highp float v = texture2D(s_texture_v, v_texcoord).r - 0.5;  
  highp float r = y +             1.402 * v;  
  highp float g = y - 0.344 * u - 0.714 * v;  
  highp float b = y + 1.772 * u;       
  gl_FragColor = vec4(r,g,b,1.0);  
}

您可以将我的代码视为在 iOS 上使用 FFmpeg 和 OpenGLES 的示例：https ://github.com/kolyvan/kxmovie 。

ffmpeg - YUV to RGB by Shader on iPhone

1 回答 1

Related

Reference