javacpp-FFmpeg系列之2:通用拉流解码器,支持视频拉流解码并转换为YUVBGR24或RGB24等图像像素数据
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javacpp-ffmpeg系列:
javacpp-FFmpeg系列之1:视频拉流解码成YUVJ420P,并保存为jpg图片
javacpp-FFmpeg系列之2:通用拉流解码器,支持视频拉流解码并转换为YUV、BGR24或RGB24等图像像素数据
javacpp-FFmpeg系列之3: 图像数据转换(BGR与BufferdImage互转,RGB与BufferdImage互转)
前言:
第一篇中视频解码成YUVJ420P图像像素数据(以下简称YUV或YUV数据),只是YUV在流媒体协议中用的较多(数据少,节省流量带宽),在图像处理应用较多的是BGR和RGB像素数据。我们已经获取到了YUV数据,那么把YUV转成BGR或者RGB需要再进行一次转换,显然性能上的表现并不是很好,所以本篇会通过编写一个通用转换器来介绍如何使用ffmpeg解码转出BGR、RGB、YUV等像素数据。
补充:
(1)为什么暂时没有用python实现,主要是先熟悉ffmpeg的API,后面会出的
(2)为什么要转成BGR、RGB像素数据,因为有了这俩其中一个就可以直接生成java的BufferImage了啊,最重要的是我们本意不是要转成BufferImage,而是直接编码成base64的图像数据啊
(3)演示demo见下一章
一、功能设计
第一篇写的很简略(实际上是那一大坨代码,自己实在看不下去了qaq),直接参考ffmpeg原生C的API,不符合java语言编写习惯,所以本篇会对上篇代码进行一些简单的封装复用。
功能上,会支持多种格式的像素数据(BGR、RGB、YUV等等);代码上,会对各个流程进行阐述分析。
二、功能实现
(1)初始化
加载ffmpeg的网络库和编解码库,不初始化就没法用,适合放在静态块中进行加载
static {
// Register all formats and codecs
av_register_all();
avformat_network_init();
}
(2)打开视频流
初始化AVFormatContext,主要就是根据url创建InputStream,并且会根据不同协议(rtmp/rtsp/hls/文件等)尝试读取一些文件头数据(流媒体头数据)。
补充:FileNotOpenException是继承自RuntimeException的自定义异常类,只是加个名字方便标识异常而已,下面还会有几个异常,都是继承自RuntimeException的自定义异常类,以下不会再提
/**
* 打开视频流
* @param url -url
* @return
* @throws FileNotOpenException
*/
protected AVFormatContext openInput(String url) throws FileNotOpenException{
AVFormatContext pFormatCtx = new AVFormatContext(null);
if(avformat_open_input(pFormatCtx, url, null, null)==0) {
return pFormatCtx;
}
throw new FileNotOpenException("Didn‘t open video file");
}
(3)检索流信息
上一步获得了AVFormatContext,这一步继续根据AVFormatContext读取一部分视音频数据并且获得一些相关的信息
/**
* 检索流信息
* @param pFormatCtx
* @return
*/
protected AVFormatContext findStreamInfo(AVFormatContext pFormatCtx) throws StreamInfoNotFoundException{
if (avformat_find_stream_info(pFormatCtx, (PointerPointer<?>) null)>= 0) {
return pFormatCtx;
}
throw new StreamInfoNotFoundException("Didn‘t retrieve stream information");
}
(3)获取视频帧
上面两步确定了媒体文件/流的上下文,这一步尝试读取一帧视频帧。
分成两个方法,先获取视频帧位置,然后根据位置获取视频帧,当然也可以合成一个方法使用。
/**
* 获取第一帧视频位置
* @param pFormatCtx
* @return
*/
protected int findVideoStreamIndex(AVFormatContext pFormatCtx) {
int i = 0, videoStream = -1;
for (i = 0; i < pFormatCtx.nb_streams(); i++) {
AVStream stream=pFormatCtx.streams(i);
AVCodecContext codec=stream.codec();
if (codec.codec_type() == AVMEDIA_TYPE_VIDEO) {
videoStream = i;
break;
}
}
return videoStream;
}
/**
* 指定视频帧位置获取对应视频帧
* @param pFormatCtx
* @param videoStream
* @return
*/
protected AVCodecContext findVideoStream(AVFormatContext pFormatCtx ,int videoStream)throws StreamNotFoundException {
if(videoStream >=0) {
// Get a pointer to the codec context for the video stream
AVStream stream=pFormatCtx.streams(videoStream);
AVCodecContext pCodecCtx = stream.codec();
return pCodecCtx;
}
throw new StreamNotFoundException("Didn‘t open video file");
}
(4)查找编解码器
其实底层调用的还是find_encdec(),遍历AVCodec链表查找有没有对应的编解码器,如果没有找到直接抛出异常,如果已经确定编解码,也可以指定codec_id
/**
* 查找并尝试打开解码器
* @return
*/
protected AVCodecContext findAndOpenCodec(AVCodecContext pCodecCtx) {
// Find the decoder for the video stream
AVCodec pCodec = avcodec_find_decoder(pCodecCtx.codec_id());
if (pCodec == null) {
System.err.println("Codec not found");
throw new CodecNotFoundExpception("Codec not found");
}
AVDictionary optionsDict = null;
// Open codec
if (avcodec_open2(pCodecCtx, pCodec, optionsDict) < 0) {
System.err.println("Could not open codec");
throw new CodecNotFoundExpception("Could not open codec"); // Could not open codec
}
return pCodecCtx;
}
(5.1)循环读取视频帧并解码成yuv
这个没什么好讲的了,前面的准备任务做完,就是一直循环读取视频帧,最后解码出来的图像帧都是yuv像素数据,这个显然不是我们想要的,所以要对这里进行改动
// Allocate video frame
AVFrame pFrame = av_frame_alloc();AVPacket packet = new AVPacket();
// Read frames and save first five frames to disk
while (av_read_frame(pFormatCtx, packet) >= 0) {
// Is this a packet from the video stream?
if (packet.stream_index() == videoStream) {
// Decode video frame
avcodec_decode_video2(pCodecCtx, pFrame, frameFinished, packet);
// Did we get a video frame?
if (frameFinished != null&&frameFinished[0] != 0) {//ffmpeg默认解码出来的是yuv数据
System.err.println(pFrame.data());
}
}
// Free the packet that was allocated by av_read_frame
av_free_packet(packet);
}
(5.2)循环读取视频帧并转换成RGB或BGR图像像素数据
// Allocate video frame
AVFrame pFrame = av_frame_alloc();
//Allocate an AVFrame structure
AVFrame pFrameRGB = av_frame_alloc();width = pCodecCtx.width();
height = pCodecCtx.height();
pFrameRGB.width(width);
pFrameRGB.height(height);
pFrameRGB.format(fmt);// Determine required buffer size and allocate buffer
int numBytes = avpicture_get_size(fmt, width, height);SwsContext sws_ctx = sws_getContext(width, height, pCodecCtx.pix_fmt(), width, height,fmt, SWS_BILINEAR, null, null, (DoublePointer) null);
BytePointer buffer = new BytePointer(av_malloc(numBytes));
// Assign appropriate parts of buffer to image planes in pFrameRGB
// Note that pFrameRGB is an AVFrame, but AVFrame is a superset
// of AVPicture
avpicture_fill(new AVPicture(pFrameRGB), buffer, fmt, width, height);
AVPacket packet = new AVPacket();
int[] frameFinished = new int[1];
// Read frames and save first five frames to disk
while (av_read_frame(pFormatCtx, packet) >= 0) {
// Is this a packet from the video stream?
if (packet.stream_index() == videoStream) {
// Decode video frame
avcodec_decode_video2(pCodecCtx, pFrame, frameFinished, packet);
// Did we get a video frame?
if (frameFinished != null&&frameFinished[0] != 0) {
// Convert the image from its native format to BGR
sws_scale(sws_ctx, pFrame.data(), pFrame.linesize(), 0, height, pFrameRGB.data(),pFrameRGB.linesize());
//Convert BGR to ByteBuffer//保存RGB或BGR数据
return saveFrame(pFrameRGB, width, height);
}
}
// Free the packet that was allocated by av_read_frame
av_free_packet(packet);
}
三、完整代码
package cc.eguid.cv.corelib.videoimageshot.grabber;
import static org.bytedeco.javacpp.avcodec.*;
import static org.bytedeco.javacpp.avformat.*;
import static org.bytedeco.javacpp.avutil.*;
import static org.bytedeco.javacpp.swscale.*;
import java.io.IOException;
import java.nio.ByteBuffer;import org.bytedeco.javacpp.BytePointer;
import org.bytedeco.javacpp.DoublePointer;
import org.bytedeco.javacpp.PointerPointer;import cc.eguid.cv.corelib.videoimageshot.exception.CodecNotFoundExpception;
import cc.eguid.cv.corelib.videoimageshot.exception.FileNotOpenException;
import cc.eguid.cv.corelib.videoimageshot.exception.StreamInfoNotFoundException;
import cc.eguid.cv.corelib.videoimageshot.exception.StreamNotFoundException;public abstract class GrabberTmplate {
static {
// Register all formats and codecs
av_register_all();
avformat_network_init();
}
//保留,暂不用
protected int width;//宽度
protected int height;//高度
/**
* 打开视频流
* @param url -url
* @return
* @throws FileNotOpenException
*/
protected AVFormatContext openInput(String url) throws FileNotOpenException{
AVFormatContext pFormatCtx = new AVFormatContext(null);
if(avformat_open_input(pFormatCtx, url, null, null)==0) {
return pFormatCtx;
}
throw new FileNotOpenException("Didn‘t open video file");
}
/**
* 检索流信息
* @param pFormatCtx
* @return
*/
protected AVFormatContext findStreamInfo(AVFormatContext pFormatCtx) throws StreamInfoNotFoundException{
if (avformat_find_stream_info(pFormatCtx, (PointerPointer<?>) null)>= 0) {
return pFormatCtx;
}
throw new StreamInfoNotFoundException("Didn‘t retrieve stream information");
}
/**
* 获取第一帧视频位置
* @param pFormatCtx
* @return
*/
protected int findVideoStreamIndex(AVFormatContext pFormatCtx) {
int i = 0, videoStream = -1;
for (i = 0; i < pFormatCtx.nb_streams(); i++) {
AVStream stream=pFormatCtx.streams(i);
AVCodecContext codec=stream.codec();
if (codec.codec_type() == AVMEDIA_TYPE_VIDEO) {
videoStream = i;
break;
}
}
return videoStream;
}
/**
* 指定视频帧位置获取对应视频帧
* @param pFormatCtx
* @param videoStream
* @return
*/
protected AVCodecContext findVideoStream(AVFormatContext pFormatCtx ,int videoStream)throws StreamNotFoundException {
if(videoStream >=0) {
// Get a pointer to the codec context for the video stream
AVStream stream=pFormatCtx.streams(videoStream);
AVCodecContext pCodecCtx = stream.codec();
return pCodecCtx;
}
throw new StreamNotFoundException("Didn‘t open video file");
}
/**
* 查找并尝试打开解码器
* @return
*/
protected AVCodecContext findAndOpenCodec(AVCodecContext pCodecCtx) {
// Find the decoder for the video stream
AVCodec pCodec = avcodec_find_decoder(pCodecCtx.codec_id());
if (pCodec == null) {
System.err.println("Codec not found");
throw new CodecNotFoundExpception("Codec not found");
}
AVDictionary optionsDict = null;
// Open codec
if (avcodec_open2(pCodecCtx, pCodec, optionsDict) < 0) {
System.err.println("Could not open codec");
throw new CodecNotFoundExpception("Could not open codec"); // Could not open codec
}
return pCodecCtx;
}
/**
* 抓取视频帧(默认跳过音频帧和空帧)
* @param url -视频源(rtsp/rtmp/hls/文件等等)
* @param fmt - 像素格式,比如AV_PIX_FMT_BGR24
* @return
* @throws IOException
*/
public ByteBuffer grabVideoFrame(String url,int fmt) throws IOException {
// Open video file
AVFormatContext pFormatCtx=openInput(url);// Retrieve stream information
pFormatCtx=findStreamInfo(pFormatCtx);// Dump information about file onto standard error
//av_dump_format(pFormatCtx, 0, url, 0);//Find a video stream
int videoStream=findVideoStreamIndex(pFormatCtx);
AVCodecContext pCodecCtx =findVideoStream(pFormatCtx,videoStream);
// Find the decoder for the video stream
pCodecCtx= findAndOpenCodec(pCodecCtx);// Allocate video frame
AVFrame pFrame = av_frame_alloc();
//Allocate an AVFrame structure
AVFrame pFrameRGB = av_frame_alloc();width = pCodecCtx.width();
height = pCodecCtx.height();
pFrameRGB.width(width);
pFrameRGB.height(height);
pFrameRGB.format(fmt);// Determine required buffer size and allocate buffer
int numBytes = avpicture_get_size(fmt, width, height);SwsContext sws_ctx = sws_getContext(width, height, pCodecCtx.pix_fmt(), width, height,fmt, SWS_BILINEAR, null, null, (DoublePointer) null);
BytePointer buffer = new BytePointer(av_malloc(numBytes));
// Assign appropriate parts of buffer to image planes in pFrameRGB
// Note that pFrameRGB is an AVFrame, but AVFrame is a superset
// of AVPicture
avpicture_fill(new AVPicture(pFrameRGB), buffer, fmt, width, height);
AVPacket packet = new AVPacket();
int[] frameFinished = new int[1];
try {
// Read frames and save first five frames to disk
while (av_read_frame(pFormatCtx, packet) >= 0) {
// Is this a packet from the video stream?
if (packet.stream_index() == videoStream) {
// Decode video frame
avcodec_decode_video2(pCodecCtx, pFrame, frameFinished, packet);
// Did we get a video frame?
if (frameFinished != null&&frameFinished[0] != 0) {
// Convert the image from its native format to BGR
sws_scale(sws_ctx, pFrame.data(), pFrame.linesize(), 0, height, pFrameRGB.data(),pFrameRGB.linesize());
//Convert BGR to ByteBuffer
return saveFrame(pFrameRGB, width, height);
}
}
// Free the packet that was allocated by av_read_frame
av_free_packet(packet);
}
return null;
}finally {
//Don‘t free buffer
// av_free(buffer);
av_free(pFrameRGB);// Free the RGB image
av_free(pFrame);// Free the YUV frame
sws_freeContext(sws_ctx);//Free SwsContext
avcodec_close(pCodecCtx);// Close the codec
avformat_close_input(pFormatCtx);// Close the video file
}
}
/**
* BGR图像帧转字节缓冲区(BGR结构)
*
* @param pFrame
* -bgr图像帧
* @param width
* -宽度
* @param height
* -高度
* @return
* @throws IOException
*/
abstract ByteBuffer saveFrame(AVFrame pFrameRGB, int width, int height);
}
四、小结
本章主要详解ffmpeg拉流解码的各个流程,可以通过本章代码可以轻松实现不限于RGB/BGR/YUV的FFmpeg所支持的多种像素格式转换
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