在iOS4.0上播放yuv420失败，但在iOS5.0上成功

Question

在iOS5.0上，从相机拍摄的视频可以很好地播放，

    glActiveTexture(GL_TEXTURE0);
    CVReturn err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault, 
                                                       videoTextureCache,
                                                       pixelBuffer,
                                                       NULL,
                                                       GL_TEXTURE_2D,
                                                       GL_RED_EXT,
                                                       videoWidth,
                                                       videoHeight,
                                                       GL_RED_EXT,
                                                       GL_UNSIGNED_BYTE,
                                                       0,
                                                       &lumaTexture);
    if (!lumaTexture || err) {
        NSLog(@"CVOpenGLESTextureCacheCreateTextureFromImage failed (error: %d)", err);  
        return;
    }

    glBindTexture(CVOpenGLESTextureGetTarget(lumaTexture), CVOpenGLESTextureGetName(lumaTexture));
    // Set texture parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);   

    glActiveTexture(GL_TEXTURE1);
    err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault, 
                                                                videoTextureCache,
                                                                pixelBuffer,
                                                                NULL,
                                                                GL_TEXTURE_2D,
                                                                GL_RG_EXT,
                                                                videoWidth / 2,
                                                                videoHeight / 2,
                                                                GL_RG_EXT,
                                                                GL_UNSIGNED_BYTE,
                                                                1,
                                                                &chromaTexture);
    if (!chromaTexture || err) {
        NSLog(@"CVOpenGLESTextureCacheCreateTextureFromImage failed (error: %d)", err);  
        return;
    }

    glBindTexture(CVOpenGLESTextureGetTarget(chromaTexture), CVOpenGLESTextureGetName(chromaTexture));
    // Set texture parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); 

在iOS4.0上，以下代码效果很好，

    CVPixelBufferLockBaseAddress(pixelBuffer, 0);
    void * baseAddress = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer,0);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, spriteTexture[0]);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RED_EXT, videoWidth, videoHeight, 0, GL_RED_EXT, GL_UNSIGNED_BYTE, baseAddress);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    void *baseAddress1 = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer,1);

    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, spriteTexture[1]);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RG_EXT, videoWidth / 2, videoHeight / 2, 0, GL_RG_EXT, GL_UNSIGNED_BYTE,baseAddress1);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);   

    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

但是当播放视频从本地mp4文件读取时，第二种方法失败了，第一种方法效果很好，很奇怪，我很妄想。那怎么解决呢？为什么会这样？