WebM VP8 SDK Usage/關于WebM VP8 SDK的用法

WebM是Google提出的新的網絡視頻格式，本質上是個MKV的殼，封裝VPX中的VP8視頻流與Vorbis OGG音頻流。目前Firefox、Opera、Chrome都能直接打開WebM視頻文件而無需其他任何亂七八糟的插件。我個人倒是很喜歡WebM的OGG音頻，雖然在低比特率下不如AAC，不過依舊勝過MP3太多了。

最近接手了一個項目，將Showcase中的Flash視頻導出替換為WebM視頻導出，著實蛋疼了一把，因為ffmpeg這個破玩意的最新二進制版本雖然集成了VPX，不過由于許可證等等原因，商業軟件不好直接使用。一氣之下我直接用Google提供的WebM SDK搞定從序列幀到視頻的輸出，完全擺脫ffmpeg。

對于WebM SDK我了找到的三個問題：

• 依舊沒有內建RGB24到YV12的轉換，不得不手動來。
• SDK提供的simple_encoder產生出的IVF依舊無法播放。
• 如果構造了一個YV12格式的vpx_image_t對象，這個對象無法重復使用，產生的視頻有錯。

下面是我的WebMEnc編碼器主文件的代碼，不明白的WebM SDK如何使用的朋友可以學習一下。JPEG、TIFF、PNG的讀取使用了FreeImage。

完整的代碼在Ortholab的SVN里有。

可執行二進制程序可以在這里下載。

// Copyright (c) 2011 Bo Zhou<Bo.Schwarzstein@gmail.com>
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//		http://www.apache.org/licenses/LICENSE-2.0 
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.#include <stdio.h>
#include <stdlib.h>#include <FreeImage.h>#include <vpx/vpx_codec.h>
#include <vpx/vpx_encoder.h>
#include <vpx/vpx_image.h>
#include <vpx/vpx_version.h>#include <vpx/vp8cx.h>#include "EbmlWriter.h"#define rgbtoy(b, g, r, y) \
y=(unsigned char)(((int)(30*r) + (int)(59*g) + (int)(11*b))/100)#define rgbtoyuv(b, g, r, y, u, v) \
rgbtoy(b, g, r, y); \
u=(unsigned char)(((int)(-17*r) - (int)(33*g) + (int)(50*b)+12800)/100); \
v=(unsigned char)(((int)(50*r) - (int)(42*g) - (int)(8*b)+12800)/100)#if defined(_MSC_VER)
/* MSVS doesn't define off_t, and uses _f{seek,tell}i64 */
#define fseeko _fseeki64
#define ftello _ftelli64
#endifvoid rgb2YUV420P(vpx_image_t *rgbImage, vpx_image_t *yv12Image)
{unsigned int width = rgbImage->w;unsigned int height = rgbImage->h;unsigned int planeSize = width * height;unsigned int halfWidth = width >> 1;unsigned char* yPlane = yv12Image->img_data;unsigned char* uPlane = yPlane + planeSize;unsigned char* vPlane = uPlane + (planeSize >> 2);static const int rgbIncrement = 3;unsigned char* rgb = rgbImage->img_data;for (unsigned int y = 0; y < height; ++ y){unsigned char* yLine = yPlane + (y * width);unsigned char* uLine = uPlane + ((y >> 1) * halfWidth);unsigned char* vLine = vPlane + ((y >> 1) * halfWidth);for (unsigned int x = 0; x < width; x += 2){rgbtoyuv(rgb[2], rgb[1], rgb[0], *yLine, *uLine, *vLine);rgb += rgbIncrement;yLine++;rgbtoyuv(rgb[2], rgb[1], rgb[0], *yLine, *uLine, *vLine);rgb += rgbIncrement;yLine++;uLine++;vLine++;}}
}bool readImage(char *filename, int frameNumber, vpx_image_t **pRGBImage, vpx_image_t **pYV12Image)
{// Load image.//char path[512];sprintf(path, filename, frameNumber);FREE_IMAGE_FORMAT format = FIF_UNKNOWN;format = FreeImage_GetFIFFromFilename(filename);if ( (format == FIF_UNKNOWN) ||((format != FIF_JPEG) &&(format != FIF_TIFF) &&(format != FIF_PNG)) ){return false;}FIBITMAP* dib = FreeImage_Load(format, path);if (dib == NULL){return false;}unsigned w = FreeImage_GetWidth(dib);unsigned h = FreeImage_GetHeight(dib);if (*pRGBImage == NULL){*pRGBImage = vpx_img_alloc(NULL, VPX_IMG_FMT_RGB24, w, h, 1);}if (*pYV12Image == NULL){*pYV12Image = vpx_img_alloc(NULL, VPX_IMG_FMT_YV12, w, h, 1);}memcpy((*pRGBImage)->img_data, FreeImage_GetBits(dib), w * h * 3);rgb2YUV420P(*pRGBImage, *pYV12Image);vpx_img_flip(*pYV12Image);FreeImage_Unload(dib);return true;
}int main(int argc, char* argv[])
{if (argc != 4){printf("  Usage: WebMEnc <filename> <bit-rates> <output file>\nExample: WebMEnc frame.%%.5d.jpg 512 frame.webm\n");return EXIT_FAILURE;}#ifdef FREEIMAGE_LIBFreeImage_Initialise();
#endif// Initialize VPX codec.//vpx_codec_ctx_t vpxContext;vpx_codec_enc_cfg_t vpxConfig;if (vpx_codec_enc_config_default(vpx_codec_vp8_cx(), &vpxConfig, 0) != VPX_CODEC_OK){return EXIT_FAILURE;}// Try to load the first frame to initialize width and height.//vpx_image_t *rgbImage = NULL, *yv12Image = NULL;if (readImage(argv[1], 0, &rgbImage, &yv12Image) == false){return EXIT_FAILURE;}vpxConfig.g_h = yv12Image->h;vpxConfig.g_w = yv12Image->w;vpxConfig.rc_target_bitrate = atoi(argv[2]);vpxConfig.g_threads = 2;// Prepare the output .webm file.//EbmlGlobal ebml;memset(&ebml, 0, sizeof(EbmlGlobal));ebml.last_pts_ms = -1;ebml.stream = fopen(argv[3], "wb");if (ebml.stream == NULL){return EXIT_FAILURE;}vpx_rational ebmlFPS = vpxConfig.g_timebase;struct vpx_rational arg_framerate = {30, 1};Ebml_WriteWebMFileHeader(&ebml, &vpxConfig, &arg_framerate);if (vpx_codec_enc_init(&vpxContext, vpx_codec_vp8_cx(), &vpxConfig, 0) != VPX_CODEC_OK){return EXIT_FAILURE;}// Reading image file sequence, encoding to .WebM file.//int frameNumber = 0;while(readImage(argv[1], frameNumber, &rgbImage, &yv12Image)){vpx_codec_err_t vpxError = vpx_codec_encode(&vpxContext, yv12Image, frameNumber, 33, 0, 0);if (vpxError != VPX_CODEC_OK){return EXIT_FAILURE;}vpx_codec_iter_t iter = NULL;const vpx_codec_cx_pkt_t *packet;while( (packet = vpx_codec_get_cx_data(&vpxContext, &iter)) ){Ebml_WriteWebMBlock(&ebml, &vpxConfig, packet);}frameNumber ++;printf("Processed %d frames.\r", frameNumber);vpx_img_free(yv12Image);yv12Image = NULL;}Ebml_WriteWebMFileFooter(&ebml, 0);fclose(ebml.stream);vpx_codec_destroy(&vpxContext);#ifdef FREEIMAGE_LIBFreeImage_DeInitialise();
#endifreturn EXIT_SUCCESS;
}