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功能很简单,大致流程为:
1) MediaCodec 解码视频文件得到 YUV、PCM 数据 2) OpenGL 将 YUV 转为 RGB,并渲染到 Surface 上 3) OpenSL/AudoTrack 获取 PCM 数据并播放需要的前置知识有:
1) YUV、PCM 等基础音视频知识,如 YUV 转 RGB 2) MediaCodec 的使用 3) OpenGL,包括 EGL、纹理等 4) OpenSL 或 AudioTrack 的使用之前写过相关的博客 ,大致流程和普通的解码类似,在编写视频播放器这个功能时,需要注意的地方有两个:
1) 监听解码流程
public interface OnDecodeListener { void onImageDecoded(byte[] data); void onSampleDecoded(byte[] data); void onDecodeEnded(); }
也可以加一个 onDecodeError() 的接口,看需要扩展即可。
2) 播放和解码同步
因为视频数据量很大,不可能把解码后的 YUV 数据保存在一个队列里,再慢慢拿出来使用 OpenGL 渲染(很容易就 OOM 了),因此,必须控制解码的速率,最简单的控制方式是和播放同步,如下所示:
ByteBuffer outputBuffer = outputBuffers[outIndex]; outputBuffer.position(bufferInfo.offset); outputBuffer.limit(bufferInfo.offset + bufferInfo.size); byte[] data = new byte[bufferInfo.size]; outputBuffer.get(data); if (mIsDecodeWithPts) { if (startTime == 0) { startTime = System.nanoTime(); } else { passTime = (System.nanoTime() - startTime) / 1000; if (passTime < bufferInfo.presentationTimeUs) { TimeUnit.MICROSECONDS.sleep(bufferInfo.presentationTimeUs - passTime); } } } if (mediaType == HWCodec.MEDIA_TYPE_VIDEO && listener != null) { listener.onImageDecoded(data); } else if (listener != null) { listener.onSampleDecoded(data); }
和渲染纹理的流程类似,不同的地方在于需要转换 YUV 数据为 RGB,而 YUV 数据又有 YUV420P、YUV420SP 等多种格式,因此在转换 RGB 之前,需要统一 YUV 数据的格式,这里使用的是 YUV420P。
YUV 数据格式之间的转换可以自己写,比如 YUV420SP 转换为 YUV420P,只需要把最后的 U、V 数据分别逐个放入到一个数组里即可,但考虑到视频裁剪、旋转,以及之后可能用到的各种 YUV 数据处理功能,因此这里引入了一个 libyuv 的库,使用非常简单:
Yuv* convertToI420(AVModel *model) { if (!model || model->imageLen <= 0 || model->flag != MODEL_FLAG_VIDEO || model->width <= 0 || model->height <= 0 || model->pixelFormat <= 0 || !model->image) { LOGE("convertToARGB failed: invalid argument"); return nullptr; } Yuv *yuv = new Yuv(model->width, model->height); ConvertToI420(model->image, (size_t) model->imageLen, yuv->bufY, yuv->strideY, yuv->bufU, yuv->strideU, yuv->bufV, yuv->strideV, 0, 0, model->width, model->height, model->width, model->height, kRotate0, getFourCC(model->pixelFormat)); return yuv;}
AVModel、Yuv 是我自定义的两个类,分别用于保存音视频数据及相关信息、YUV 数据及相关信息,源码可见 。
YUV 转 RGB 的相关系数在 介绍过,可以在 fragment shader 完成:
#version 300 esprecision highp float;uniform sampler2D yTexture;uniform sampler2D uTexture;uniform sampler2D vTexture;in vec2 vTexCoord;layout(location=0) out vec4 fragColor;void main() { highp float y = texture(yTexture, vTexCoord).r; highp float u = texture(uTexture, vTexCoord).r - 0.5; highp float v = texture(vTexture, vTexCoord).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; fragColor = vec4(r, g, b, 1.0);}
OpenGL 关键代码如下:
bool YuvRenderer::doInit() { std::string *vShader = readShaderFromAsset(mAssetManager, "yuv_renderer.vert"); std::string *fShader = readShaderFromAsset(mAssetManager, "yuv_renderer.frag"); mProgram = loadProgram(vShader->c_str(), fShader->c_str()); mMatrixLoc = glGetUniformLocation(mProgram, "mMatrix"); mSamplerY = glGetUniformLocation(mProgram, "yTexture"); mSamplerU = glGetUniformLocation(mProgram, "uTexture"); mSamplerV = glGetUniformLocation(mProgram, "vTexture"); glPixelStorei(GL_UNPACK_ALIGNMENT, 1); // 生成三个纹理,分别用于装载 Y、U、V 数据 glGenTextures(3, mTextures); glBindTexture(GL_TEXTURE_2D, mTextures[0]); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, mTexWidth, mTexHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glBindTexture(GL_TEXTURE_2D, mTextures[1]); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, mTexWidth / 2, mTexHeight / 2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glBindTexture(GL_TEXTURE_2D, mTextures[2]); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, mTexWidth / 2, mTexHeight / 2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // 缓存顶点坐标、纹理坐标、索引数据到 VBO 中 glGenBuffers(3, mVboIds); glBindBuffer(GL_ARRAY_BUFFER, mVboIds[0]); glBufferData(GL_ARRAY_BUFFER, sizeof(VERTICES), VERTICES, GL_STATIC_DRAW); glBindBuffer(GL_ARRAY_BUFFER, mVboIds[1]); glBufferData(GL_ARRAY_BUFFER, sizeof(TEX_COORDS), TEX_COORDS, GL_STATIC_DRAW); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mVboIds[2]); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(INDICES), INDICES, GL_STATIC_DRAW); // 缓存 VBO 到 VAO 中 glGenVertexArrays(1, &mVaoId); glBindVertexArray(mVaoId); glBindBuffer(GL_ARRAY_BUFFER, mVboIds[0]); glEnableVertexAttribArray(ATTRIB_POSITION); glVertexAttribPointer(ATTRIB_POSITION, VERTEX_POS_SIZE, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * VERTEX_POS_SIZE, 0); glBindBuffer(GL_ARRAY_BUFFER, mVboIds[1]); glEnableVertexAttribArray(ATTRIB_TEX_COORD); glVertexAttribPointer(ATTRIB_TEX_COORD, TEX_COORD_SIZE, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * TEX_COORD_SIZE, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mVboIds[2]); glBindVertexArray(0); glBindBuffer(GL_ARRAY_BUFFER, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); glClearColor(1.0f, 1.0f, 1.0f, 1.0f); delete vShader; delete fShader; return true;}void YuvRenderer::doDraw() { glViewport(0, 0, mWidth, mHeight); glClear(GL_COLOR_BUFFER_BIT); glUseProgram(mProgram); glUniformMatrix4fv(mMatrixLoc, 1, GL_FALSE, mMatrix); if (!mYuv) { LOGW("YuvRenderer doDraw failed: yuv data have not assigned"); return; } // 分别载入 Y、U、V 数据到对应的纹理中 glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, mTextures[0]); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, mTexWidth, mTexHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, mYuv->bufY); glUniform1i(mSamplerY, 0); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, mTextures[1]); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, mTexWidth / 2, mTexHeight / 2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, mYuv->bufU); glUniform1i(mSamplerU, 1); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, mTextures[2]); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, mTexWidth / 2, mTexHeight / 2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, mYuv->bufV); glUniform1i(mSamplerV, 2); // 使用 VAO 缓存的数据绘制图像 glBindVertexArray(mVaoId); glDrawElements(GL_TRIANGLES, INDEX_NUMBER, GL_UNSIGNED_SHORT, 0); glBindVertexArray(0); glBindTexture(GL_TEXTURE_2D, 0);}
初始化播放器:
bool BQAudioPlayer::init() { SLresult result; SLDataLocator_AndroidSimpleBufferQueue locBufq = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE, 2}; // channelMask: 位数和 channel 相等,0 代表 SL_SPEAKER_FRONT_LEFT | SL_SPEAKER_FRONT_RIGHT SLDataFormat_PCM formatPcm = {SL_DATAFORMAT_PCM, (SLuint32) mChannels, mSampleRate, (SLuint32) mSampleFormat, (SLuint32) mSampleFormat, mChannels == 2 ? 0 : SL_SPEAKER_FRONT_CENTER, SL_BYTEORDER_LITTLEENDIAN}; if (mSampleRate) { formatPcm.samplesPerSec = mSampleRate; } SLDataSource audioSrc = {&locBufq, &formatPcm}; SLDataLocator_OutputMix locOutpuMix = {SL_DATALOCATOR_OUTPUTMIX, mAudioEngine->outputMixObj}; SLDataSink audioSink = {&locOutpuMix, nullptr}; const SLInterfaceID ids[3] = {SL_IID_BUFFERQUEUE, SL_IID_VOLUME, SL_IID_EFFECTSEND}; const SLboolean req[3] = {SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE}; result = (*mAudioEngine->engine)->CreateAudioPlayer(mAudioEngine->engine, &mPlayerObj, &audioSrc, &audioSink, mSampleRate ? 2 : 3, ids, req); if (result != SL_RESULT_SUCCESS) { LOGE("CreateAudioPlayer failed: %d", result); return false; } result = (*mPlayerObj)->Realize(mPlayerObj, SL_BOOLEAN_FALSE); if (result != SL_RESULT_SUCCESS) { LOGE("mPlayerObj Realize failed: %d", result); return false; } result = (*mPlayerObj)->GetInterface(mPlayerObj, SL_IID_PLAY, &mPlayer); if (result != SL_RESULT_SUCCESS) { LOGE("mPlayerObj GetInterface failed: %d", result); return false; } result = (*mPlayerObj)->GetInterface(mPlayerObj, SL_IID_BUFFERQUEUE, &mBufferQueue); if (result != SL_RESULT_SUCCESS) { LOGE("mPlayerObj GetInterface failed: %d", result); return false; } result = (*mBufferQueue)->RegisterCallback(mBufferQueue, playerCallback, this); if (result != SL_RESULT_SUCCESS) { LOGE("mPlayerObj RegisterCallback failed: %d", result); return false; } mEffectSend = nullptr; if (mSampleRate == 0) { result = (*mPlayerObj)->GetInterface(mPlayerObj, SL_IID_EFFECTSEND, &mEffectSend); if (result != SL_RESULT_SUCCESS) { LOGE("mPlayerObj GetInterface failed: %d", result); return false; } } result = (*mPlayerObj)->GetInterface(mPlayerObj, SL_IID_VOLUME, &mVolume); if (result != SL_RESULT_SUCCESS) { LOGE("mPlayerObj GetInterface failed: %d", result); return false; } result = (*mPlayer)->SetPlayState(mPlayer, SL_PLAYSTATE_PLAYING); if (result != SL_RESULT_SUCCESS) { LOGE("mPlayerObj SetPlayState failed: %d", result); return false; } return true;}
之后只需要把 PCM 入队即可:
// 一帧音频播放完毕后就会回调这个函数void playerCallback(SLAndroidSimpleBufferQueueItf bq, void *context) { BQAudioPlayer *player = (BQAudioPlayer *) context; assert(bq == player->mBufferQueue); pthread_mutex_unlock(&player->mMutex);}void BQAudioPlayer::enqueueSample(void *data, size_t length) { // 必须等待一帧音频播放完毕后才可以 Enqueue 第二帧音频 pthread_mutex_lock(&mMutex); if (mBufSize < length) { mBufSize = length; if (mBuffers[0]) { delete[] mBuffers[0]; } if (mBuffers[1]) { delete[] mBuffers[1]; } mBuffers[0] = new uint8_t[mBufSize]; mBuffers[1] = new uint8_t[mBufSize]; } memcpy(mBuffers[mIndex], data, length); (*mBufferQueue)->Enqueue(mBufferQueue, mBuffers[mIndex], length); mIndex = 1 - mIndex;}
结束播放:
void BQAudioPlayer::release() { pthread_mutex_lock(&mMutex); if (mPlayerObj) { (*mPlayerObj)->Destroy(mPlayerObj); mPlayerObj = nullptr; mPlayer = nullptr; mBufferQueue = nullptr; mEffectSend = nullptr; mVolume = nullptr; } if (mAudioEngine) { delete mAudioEngine; mAudioEngine = nullptr; } if (mBuffers[0]) { delete[] mBuffers[0]; mBuffers[0] = nullptr; } if (mBuffers[1]) { delete[] mBuffers[1]; mBuffers[1] = nullptr; } pthread_mutex_unlock(&mMutex); pthread_mutex_destroy(&mMutex);}
相对 OpenSL,AudioTrack 代码量少很多,设置 AudioTrack:
private void setupAudioTrack() { int channelConfig = mChannels == 1 ? AudioFormat.CHANNEL_OUT_MONO : AudioFormat.CHANNEL_OUT_STEREO; // 获取 sample format 的 API 要求高,这里默认使用 ENCODING_PCM_16BIT int bufferSize = AudioTrack.getMinBufferSize(mSampleRate, channelConfig, AudioFormat.ENCODING_PCM_16BIT); mAudioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, mSampleRate, channelConfig, AudioFormat.ENCODING_PCM_16BIT, bufferSize, AudioTrack.MODE_STREAM); }
播放 PCM 数据:
@Override public void onSampleDecoded(byte[] data) { if (mIsPlaying) { mAudioTrack.write(data, 0, data.length); mAudioTrack.play(); } }
结束播放:
private void releaseAudioTrack() { if (mAudioTrack != null) { mAudioTrack.stop(); mAudioTrack.release(); mAudioTrack = null; } }
以上,一款简单的视频播放器就完成了,如果觉得哪些代码写得不够好,请留言交流一下,谢谢。
源码已上传到 。
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