最简单的基于 FFmpeg 的内存读写的例子:内存转码器
- 最简单的基于 FFmpeg 的内存读写的例子:内存转码器
- 正文
- 源程序
- 结果
- 工程文件下载
- 参考链接
最简单的基于 FFmpeg 的内存读写的例子:内存转码器
参考雷霄骅博士的文章,链接:最简单的基于FFmpeg的内存读写的例子:内存播放器
正文
之前的所有有关 FFmpeg 的例子都是对文件进行操作的。实际上,并不是所有视频的编码,解码都是针对文件进行处理的。有的时候需要的解码的视频数据在一段内存中。例如,通过其他系统送来的视频数据。同样,有的时候编码后的视频数据也未必要保存成一个文件。例如,要求将编码后的视频数据送给其他的系统进行下一步的处理。以上两种情况就要求 FFmpeg 不仅仅是对文件进行“读,写”操作,而是要对内存进行“读,写”操作。因此打算记录的两个例子就是使用 FFmpeg 对内存进行读写的例子。
这篇文章记录一个基于 FFmpeg 的内存转码器。该转码器可以使用 FFmpeg 读取内存中的数据,转码为 H.264 之后再将数据输出到内存。
关于如何从内存中读取数据在这里不再详述,可以参考文章:《ffmpeg 从内存中读取数据(或将数据输出到内存)》。
FFmpeg 读写内存的关键点就两个:
第一,初始化自定义的 AVIOContext,指定自定义的回调函数。示例代码如下:
//AVIOContext中的缓存
unsigned char *aviobuffer=(unsigned char*)av_malloc(32768);
AVIOContext *avio=avio_alloc_context(aviobuffer, 32768,0,NULL,read_buffer,NULL,NULL);
pFormatCtx->pb=avio;if(avformat_open_input(&pFormatCtx,NULL,NULL,NULL)!=0){printf("Couldn't open inputstream.(无法打开输入流)\n");return -1;
}
上述代码中,自定义了回调函数 read_buffer()。在使用 avformat_open_input() 打开媒体数据的时候,就可以不指定文件的 URL 了,即其第 2 个参数为 NULL(因为数据不是靠文件读取,而是由 read_buffer() 提供)。
第二,自己写回调函数。注意函数的参数和返回值(尤其是返回值)。示例代码如下:
//Callback
int read_buffer(void *opaque, uint8_t *buf, int buf_size){if(!feof(fp_open)){inttrue_size=fread(buf,1,buf_size,fp_open);return true_size;}else{return -1;}
}
当系统需要数据的时候,会自动调用该回调函数以获取数据。这个例子为了简单,直接使用 fread() 读取数据至内存。回调函数需要格外注意它的参数和返回值。
转码实际上就是解码和编码的结合。该方面的知识可以参考文章:
- 解码:100行代码实现最简单的基于FFMPEG+SDL的视频播放器(SDL1.x)
- 编码:最简单的基于FFMPEG的视频编码器(YUV编码为H.264)
- 转码: 最简单的基于FFMPEG的转码程序
程序的流程图如下图所示。从图中可以看出,首先分别初始化了输入和输出的 AVFormatContext。然后首先解码输入的 AVPacket,得到存储像素数据(YUV420P 格式)的 AVFrame,然后编码 AVFrame 为 H.264 的 AVPacket,最后将编码后的 AVPacket 输出。
源程序
/**
* 最简单的基于FFmpeg的内存读写例子(内存转码器)
* Simplest FFmpeg mem Transcoder
*
* 源程序:
* 雷霄骅,张晖
* leixiaohua1020@126.com
* 中国传媒大学/数字电视技术
* Communication University of China / Digital TV Technology
* http://blog.csdn.net/leixiaohua1020
*
* 修改:
* 刘文晨 Liu Wenchen
* 812288728@qq.com
* 电子科技大学/电子信息
* University of Electronic Science and Technology of China / Electronic and Information Science
* https://blog.csdn.net/ProgramNovice
*
* 本程序实现了任意格式视频数据(例如 MPEG2)转码为 H.264 码流数据。
* 本程序并不是对文件进行处理,而是对内存中的视频数据进行处理。
* 它从内存读取数据,并且将转码后的数据输出到内存中。
* 是最简单的使用 FFmpeg 读写内存的例子。
*
* This software convert video bitstream (Such as MPEG2) to H.264
* bitstream. It read video bitstream from memory (not from a file),
* convert it to H.264 bitstream, and finally output to another memory.
* It's the simplest example to use FFmpeg to read (or write) from
* memory.
*
*/#include "stdafx.h"#include <stdio.h>#define __STDC_CONSTANT_MACROS#ifdef _WIN32
// Windows
extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/avutil.h"
#include "libavutil/opt.h"
#include "libavutil/pixdesc.h"
};
#else
// Linux...
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/avutil.h>
#include <libavutil/opt.h>
#include <libavutil/pixdesc.h>
#ifdef __cplusplus
};
#endif
#endifFILE *fp_open;
FILE *fp_write;// Read File
int read_buffer(void *opaque, uint8_t *buf, int buf_size)
{if (!feof(fp_open)){int true_size = fread(buf, 1, buf_size, fp_open);return true_size;}else{return -1;}
}// Write File
int write_buffer(void *opaque, uint8_t *buf, int buf_size)
{if (!feof(fp_write)){int true_size = fwrite(buf, 1, buf_size, fp_write);return true_size;}else{return -1;}
}int flush_encoder(AVFormatContext *fmt_ctx, unsigned int stream_index)
{int ret;int got_frame;AVPacket enc_pkt;if (!(fmt_ctx->streams[stream_index]->codec->codec->capabilities &CODEC_CAP_DELAY))return 0;while (1){av_log(NULL, AV_LOG_INFO, "Flushing stream #%u encoder\n", stream_index);//ret = encode_write_frame(NULL, stream_index, &got_frame);enc_pkt.data = NULL;enc_pkt.size = 0;av_init_packet(&enc_pkt);ret = avcodec_encode_video2(fmt_ctx->streams[stream_index]->codec, &enc_pkt,NULL, &got_frame);av_frame_free(NULL);if (ret < 0)break;if (!got_frame){ret = 0;break;}// prepare packet for muxingenc_pkt.stream_index = stream_index;enc_pkt.dts = av_rescale_q_rnd(enc_pkt.dts,fmt_ctx->streams[stream_index]->codec->time_base,fmt_ctx->streams[stream_index]->time_base,(AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));enc_pkt.pts = av_rescale_q_rnd(enc_pkt.pts,fmt_ctx->streams[stream_index]->codec->time_base,fmt_ctx->streams[stream_index]->time_base,(AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));enc_pkt.duration = av_rescale_q(enc_pkt.duration,fmt_ctx->streams[stream_index]->codec->time_base,fmt_ctx->streams[stream_index]->time_base);av_log(NULL, AV_LOG_DEBUG, "Muxing frame.\n");// mux encoded frameret = av_write_frame(fmt_ctx, &enc_pkt);if (ret < 0)break;}return ret;
}int main(int argc, char* argv[])
{int ret;AVFormatContext *ifmt_ctx = NULL;AVFormatContext *ofmt_ctx = NULL;AVPacket packet, enc_pkt;AVFrame *frame = NULL;enum AVMediaType type;unsigned int stream_index;unsigned int i = 0;int got_frame, enc_got_frame;AVStream *out_stream;AVStream *in_stream;AVCodecContext *dec_ctx, *enc_ctx;AVCodec *encoder;fp_open = fopen("cuc60anniversary_start.ts", "rb"); // 视频源文件 fp_write = fopen("cuc60anniversary_start.h264", "wb+"); // 输出文件av_register_all();ifmt_ctx = avformat_alloc_context();avformat_alloc_output_context2(&ofmt_ctx, NULL, "h264", NULL);unsigned char* inbuffer = NULL;unsigned char* outbuffer = NULL;inbuffer = (unsigned char*)av_malloc(32768);outbuffer = (unsigned char*)av_malloc(32768);AVIOContext *avio_in = NULL;AVIOContext *avio_out = NULL;// open input fileavio_in = avio_alloc_context(inbuffer, 32768, 0, NULL, read_buffer, NULL, NULL);if (avio_in == NULL)goto end;ifmt_ctx->pb = avio_in;ifmt_ctx->flags = AVFMT_FLAG_CUSTOM_IO;if ((ret = avformat_open_input(&ifmt_ctx, "whatever", NULL, NULL)) < 0){av_log(NULL, AV_LOG_ERROR, "Cannot open input file.\n");return ret;}if ((ret = avformat_find_stream_info(ifmt_ctx, NULL)) < 0){av_log(NULL, AV_LOG_ERROR, "Cannot find stream information.\n");return ret;}for (i = 0; i < ifmt_ctx->nb_streams; i++){AVStream *stream;AVCodecContext *codec_ctx;stream = ifmt_ctx->streams[i];codec_ctx = stream->codec;// Reencode video & audio and remux subtitles etcif (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO){// Open decoderret = avcodec_open2(codec_ctx,avcodec_find_decoder(codec_ctx->codec_id), NULL);if (ret < 0){av_log(NULL, AV_LOG_ERROR, "Failed to open decoder for stream #%u.\n", i);return ret;}}}// Print some input information//av_dump_format(ifmt_ctx, 0, "whatever", 0);// open output fileavio_out = avio_alloc_context(outbuffer, 32768, 1, NULL, NULL, write_buffer, NULL);if (avio_out == NULL)goto end;//avio_out->write_packet=write_packet;ofmt_ctx->pb = avio_out;ofmt_ctx->flags = AVFMT_FLAG_CUSTOM_IO;for (i = 0; i < 1; i++){out_stream = avformat_new_stream(ofmt_ctx, NULL);if (!out_stream){av_log(NULL, AV_LOG_ERROR, "Failed allocating output stream.\n");return AVERROR_UNKNOWN;}in_stream = ifmt_ctx->streams[i];dec_ctx = in_stream->codec;enc_ctx = out_stream->codec;if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO){encoder = avcodec_find_encoder(AV_CODEC_ID_H264);enc_ctx->height = dec_ctx->height;enc_ctx->width = dec_ctx->width;enc_ctx->sample_aspect_ratio = dec_ctx->sample_aspect_ratio;enc_ctx->pix_fmt = encoder->pix_fmts[0];enc_ctx->time_base = dec_ctx->time_base;//enc_ctx->time_base.num = 1;//enc_ctx->time_base.den = 25;// H.264的必备选项,没有就会错enc_ctx->me_range = 16;enc_ctx->max_qdiff = 4;enc_ctx->qmin = 10;enc_ctx->qmax = 51;enc_ctx->qcompress = 0.6;enc_ctx->refs = 3;enc_ctx->bit_rate = 500000;ret = avcodec_open2(enc_ctx, encoder, NULL);if (ret < 0){av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u.\n", i);return ret;}}else if (dec_ctx->codec_type == AVMEDIA_TYPE_UNKNOWN){av_log(NULL, AV_LOG_FATAL, "Elementary stream #%d is of unknown type, cannot proceed.\n", i);return AVERROR_INVALIDDATA;}else{// if this stream must be remuxedret = avcodec_copy_context(ofmt_ctx->streams[i]->codec,ifmt_ctx->streams[i]->codec);if (ret < 0){av_log(NULL, AV_LOG_ERROR, "Copying stream context failed.\n");return ret;}}if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)enc_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;}// Print some output information//av_dump_format(ofmt_ctx, 0, "whatever", 1);// init muxer, write output file headerret = avformat_write_header(ofmt_ctx, NULL);if (ret < 0){av_log(NULL, AV_LOG_ERROR, "Error occurred when opening output file.\n");return ret;}i = 0;// read all packetswhile (1){i++;if ((ret = av_read_frame(ifmt_ctx, &packet)) < 0)break;stream_index = packet.stream_index;if (stream_index != 0)continue;type = ifmt_ctx->streams[packet.stream_index]->codec->codec_type;av_log(NULL, AV_LOG_DEBUG, "Demuxer gave frame of stream_index %u.\n",stream_index);av_log(NULL, AV_LOG_DEBUG, "Going to reencode the frame.\n");frame = av_frame_alloc();if (!frame){ret = AVERROR(ENOMEM);break;}// 解压缩时间戳packet.dts = av_rescale_q_rnd(packet.dts,ifmt_ctx->streams[stream_index]->time_base,ifmt_ctx->streams[stream_index]->codec->time_base,(AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));// 显示时间戳packet.pts = av_rescale_q_rnd(packet.pts,ifmt_ctx->streams[stream_index]->time_base,ifmt_ctx->streams[stream_index]->codec->time_base,(AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));// 解码输入文件ret = avcodec_decode_video2(ifmt_ctx->streams[stream_index]->codec, frame,&got_frame, &packet);printf("Decode 1 Packet\tsize:%d\tpts:%lld.\n", packet.size, packet.pts);if (ret < 0){av_frame_free(&frame);av_log(NULL, AV_LOG_ERROR, "Decoding failed.\n");break;}if (got_frame){frame->pts = av_frame_get_best_effort_timestamp(frame);frame->pict_type = AV_PICTURE_TYPE_NONE;enc_pkt.data = NULL;enc_pkt.size = 0;av_init_packet(&enc_pkt);ret = avcodec_encode_video2(ofmt_ctx->streams[stream_index]->codec, &enc_pkt,frame, &enc_got_frame);printf("Encode 1 Packet\tsize:%d\tpts:%lld.\n", enc_pkt.size, enc_pkt.pts);av_frame_free(&frame);if (ret < 0)goto end;if (!enc_got_frame)continue;// prepare packet for muxingenc_pkt.stream_index = stream_index;enc_pkt.dts = av_rescale_q_rnd(enc_pkt.dts,ofmt_ctx->streams[stream_index]->codec->time_base,ofmt_ctx->streams[stream_index]->time_base,(AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));enc_pkt.pts = av_rescale_q_rnd(enc_pkt.pts,ofmt_ctx->streams[stream_index]->codec->time_base,ofmt_ctx->streams[stream_index]->time_base,(AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));enc_pkt.duration = av_rescale_q(enc_pkt.duration,ofmt_ctx->streams[stream_index]->codec->time_base,ofmt_ctx->streams[stream_index]->time_base);av_log(NULL, AV_LOG_INFO, "Muxing frame %d.\n", i);// mux encoded frameav_write_frame(ofmt_ctx, &enc_pkt);if (ret < 0)goto end;}else{av_frame_free(&frame);}av_free_packet(&packet);}// flush encodersfor (i = 0; i < 1; i++){// flush encoderret = flush_encoder(ofmt_ctx, i);if (ret < 0){av_log(NULL, AV_LOG_ERROR, "Flushing encoder failed.\n");goto end;}}// Write file trailerav_write_trailer(ofmt_ctx);end:// avio_in 释放之前需要先释放 avio_in->buffer, 否则会出现内存泄漏av_free(avio_in->buffer);av_freep(&avio_in);av_free(avio_out->buffer);av_freep(&avio_out);av_free(inbuffer);av_free(outbuffer);av_free_packet(&packet);av_frame_free(&frame);avformat_close_input(&ifmt_ctx);avformat_free_context(ofmt_ctx);//fcloseall();fclose(fp_open);fclose(fp_write);if (ret < 0)av_log(NULL, AV_LOG_ERROR, "Error occurred.\n");return (ret ? 1 : 0);
}
结果
一开始会报错:
属性页将 SDL 检查设置为否:
程序的运行结果如下:
输入文件:
输出文件:
工程文件下载
GitHub:UestcXiye / Simplest-FFmpeg-Memory-Transcoder
CSDN:Simplest FFmpeg Memory Transcoder.zip
参考链接
- ffmpeg 从内存中读取数据(或将数据输出到内存)
- 100行代码实现最简单的基于FFMPEG+SDL的视频播放器(SDL1.x)
- 最简单的基于FFMPEG的视频编码器(YUV编码为H.264)
- 最简单的基于FFMPEG的转码程序