FFMPEG一些color属性
ffmpeg color有四个属性color space、transfer function、primaries、range，四个属性，定义主要见libavutils/pixfmt.h中，以AVCOL_前缀的几个enum类型。
1, color space: YUV是基于RGB的颜色空间，color space属性是决定了YUV2RGB/RGB2YUV的转换计算matrix
2, color primaries：基于的RGB空间对应的绝对颜色XYZ的变换，决定了最终三原色RGB分别是什么颜色
3, color transfer：定义了transfer funciton的gamma值，从RGB到最终显示的值需要进行gamma压暗，比如bt709的平均gamma为1.96
4，color range：pc range和tv range（又叫video range和full range），full range中YUV的取值[0-255]，video range中Y[16-235]，UV [16-240]
这4个值默认都是UnSpecified，这种情况下对于不同的播放器解释行为不太一致，要注意一下，可能会造成不同播放器下的颜色不一致，建议是已知的color属性在播放、转码的时候切记都要考虑！
shaders相关
移动端中在播放视频的时候需要YUV转RGB，直接拿SwsContext转太慢了，可以使用shader来完成，需要注意转换矩阵问题：
1，YUV2RGB
// Reference http://www.equasys.de/colorconversion.html
static const GLfloat kBt709VideoRangeYUV2RGBMatrix[] = {
1.164, 1.164, 1.164,
0.0, -0.213, 2.112,
1.793, -0.533, 0.0,
};
// not found bt709 full range matrix, identical with video range
static const GLfloat kBt709FullRangeYUV2RGBMatrix[] = {
1.164, 1.164, 1.164,
0.0, -0.213, 2.112,
1.793, -0.533, 0.0,
};
static const GLfloat kBt601VideoRangeYUV2RGBMatrix[] = {
1.164, 1.164, 1.164,
0.0, -0.392, 2.017,
1.596, -0.813, 0.0,
};
static const GLfloat kBt601FullRangeYUV2RGBMatrix[] = {
1.0, 1.0, 1.0,
0.0, -0.343, 1.765,
1.4, -0.711, 0.0,
};
static const char* kGlvsYuv420pToRgb =
" // Vertex Shader \n"
" precision highp float; \n"
" attribute highp vec4 a_position; \n"
" attribute highp vec2 a_texCoord0; \n"
" varying highp vec2 v_texCoord0; \n"
" void main(void) \n"
" { \n"
" gl_Position = a_position; \n"
" v_texCoord0 = vec2(a_texCoord0.x,1.0-a_texCoord0.y); \n"
" } \n";
static const char* kGlfsYuv420pToRgb =
" // Pixel Shader \n"
" precision highp float; \n"
" uniform lowp sampler2D ImageInput0 ; \n"
" uniform lowp sampler2D ImageInput1 ; \n"
" uniform lowp sampler2D ImageInput2 ; \n"
" varying highp vec2 v_texCoord0; \n"
" uniform float y_offset; \n"
" uniform mat3 um3_ColorConversion; \n"
" \n"
" void main(void) \n"
" { \n"
" mediump vec3 yuv; \n"
" lowp vec3 rgb; \n"
" yuv.x = texture2D(ImageInput0, v_texCoord0.xy).r - (y_offset / 255.0); \n"
" yuv.y = texture2D(ImageInput1, v_texCoord0.xy).r - 0.5; \n"
" yuv.z = texture2D(ImageInput2, v_texCoord0.xy).r - 0.5; \n"
" rgb = um3_ColorConversion * yuv; \n"
" \n"
" gl_FragColor = vec4(rgb, 1.0); \n"
" } \n";
} // namespace
2，RGB2YUV
static const GLfloat kBt709VideoRangeRGB2YUVMatrix[] = {
0.183, -0.101, 0.439,
0.614, -0.339, -0.399,
0.062, 0.439, -0.040,
};
// Not found bt709 full range, identical as video range for now
static const GLfloat kBt709FullRangeRGB2YUVMatrix[] = {
0.183, -0.101, 0.439,
0.614, -0.339, -0.399,
0.062, 0.439, -0.040,
};
static const GLfloat kBt601VideoRangeRGB2YUVMatrix[] = {
0.257, -0.148, 0.439,
0.504, -0.291, -0.368,
0.098, 0.439, -0.071,
};
static const GLfloat kBt601FullRangeRGB2YUVMatrix[] = {
0.299, -0.169, 0.500,
0.587, -0.331, -0.419,
0.114, 0.500, -0.081,
};
// Reference: http://www.equasys.de/colorconversion.html
static const char* kGlfsRgbToYuv420p =
" // Pixel Shader \n"
" precision highp float; \n"
" uniform sampler2D ImageSampler; \n"
" varying vec2 v_texCoord0; \n"
" uniform mat3 um3_ColorConversion; \n"
" uniform float y_offset; \n"
" \n"
" void main(void) \n"
" { \n"
" lowp vec3 yuv; \n"
" \n"
" vec4 rgba = texture2D(ImageSampler, v_texCoord0.xy); \n"
" yuv = um3_ColorConversion * rgba.rgb; \n"
" yuv.r = yuv.r + (y_offset / 255.0); \n"
" yuv.g = yuv.g + 0.5; \n"
" yuv.b = yuv.b + 0.5; \n "
" gl_FragColor = vec4(yuv, 1.0); \n"
" } \n";
VideoToolBox相关
使用VT来硬解视频的时候支持直接输出RGB（kCVPixelFormatType_32BGRA等RGB空间的输出），也能够使用硬件加速，不过要注意color相关问题，否则会偏色。ffmpeg中和VT中对于color一些属性的name方式不一样。
if (avctx->color_primaries == AVCOL_PRI_BT709) {
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Primaries to BT709\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_ColorPrimaries,
kCMFormatDescriptionColorPrimaries_ITU_R_709_2);
} else if (avctx->color_primaries == AVCOL_PRI_SMPTE170M
|| avctx->color_primaries == AVCOL_PRI_SMPTE240M) {
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Primaries to SMPTE_C\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_ColorPrimaries,
kCMFormatDescriptionColorPrimaries_SMPTE_C);
} else if (avctx->color_primaries == AVCOL_SPC_BT470BG) {
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Primaries to EBU_3213\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_ColorPrimaries,
kCMFormatDescriptionColorPrimaries_EBU_3213);
} else {
av_log(avctx, AV_LOG_INFO, "Did not set VideoToolbox Color Primaries for %d\n", avctx->color_primaries);
}
if (avctx->color_trc == AVCOL_TRC_BT709
|| avctx->color_trc == AVCOL_TRC_BT2020_10
|| avctx->color_trc == AVCOL_TRC_BT2020_12)
{
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Transfer Function to BT709\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_TransferFunction,
kCMFormatDescriptionTransferFunction_ITU_R_709_2);
} else if (avctx->color_trc == AVCOL_TRC_SMPTE170M || avctx->color_trc == AVCOL_TRC_SMPTE240M) {
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Transfer Function to SMPTE_240M_1995\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_TransferFunction,
kCMFormatDescriptionTransferFunction_SMPTE_240M_1995);
} else {
av_log(avctx, AV_LOG_INFO, "Did not set VideoToolbox Color Transfer Function for %d\n", avctx->color_trc);
}
if (avctx->colorspace == AVCOL_SPC_BT709) {
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Space to BT709\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_YCbCrMatrix,
kCMFormatDescriptionYCbCrMatrix_ITU_R_709_2);
} else if (avctx->colorspace == AVCOL_SPC_SMPTE170M || avctx->colorspace == AVCOL_SPC_BT470BG) {
// TODO: not sure for now whether AVCOL_SPC_BT470BG use 601_4
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Space to ITU_R_601_4\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_YCbCrMatrix,
kCMFormatDescriptionYCbCrMatrix_ITU_R_601_4);
} else if (avctx->colorspace == AVCOL_SPC_SMPTE240M) {
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Space to 240M_1995\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_YCbCrMatrix,
kCMFormatDescriptionYCbCrMatrix_SMPTE_240M_1995);
} else {
av_log(avctx, AV_LOG_INFO, "Did not set VideoToolbox Color Space for %d\n", avctx->colorspace);
}
if (avctx->color_range == AVCOL_RANGE_JPEG) {
av_log(avctx, AV_LOG_INFO, "Setting VideoToolbox Color Range to full range\n");
CFDictionarySetValue(config_info,
kCMFormatDescriptionExtension_FullRangeVideo,
kCFBooleanTrue);
} else {
av_log(avctx, AV_LOG_INFO, "Did not set VideoToolbox Color Range, will use video-range by default\n");
}