FFMPEG解复用、解码测试，音频保存WAV文件，视频保存为PPM图像1. WAV(PCM)文件格式分析

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我是靠谱客的博主虚心树叶，最近开发中收集的这篇文章主要介绍FFMPEG解复用、解码测试，音频保存WAV文件，视频保存为PPM图像1. WAV(PCM)文件格式分析，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

1. WAV(PCM)文件格式分析

WAVE文件作为多媒体中使用的声波文件格式之一，它是以RIFF格式为标准的。
RIFF是英文Resource Interchange File Format的缩写，每个WAVE文件的头四个字节便是“RIFF”。
WAVE文件由文件头和数据体两大部分组成。其中文件头又分为RIFF／WAV文件标识段和声音数据格式说明段两部分。
WAVE文件各部分内容及格式见附表。
　　常见的声音文件主要有两种，分别对应于单声道（11.025KHz采样率、8Bit的采样值）和双声道（44.1KHz采样率、16Bit的采样值）。
采样率是指：声音信号在“模→数”转换过程中单位时间内采样的次数。采样值是指每一次采样周期内声音模拟信号的积分值。
　　对于单声道声音文件，采样数据为八位的短整数（short int 00H-FFH）；而对于双声道立体声声音文件，每次采样数据为一个16位的整数（int），高八位和低八位分别代表左右两个声道。
WAVE文件数据块包含以脉冲编码调制（PCM）格式表示的样本。WAVE文件是由样本组织而成的。
在单声道WAVE文件中，声道0代表左声道，声道1代表右声道。在多声道WAVE文件中，样本是交替出现的。
　　WAVE文件格式说明表　　
　　偏移地址字节数数据类型内容
　
　　文件头
　　00H 4 char "RIFF"标志
　　04H 4 long int 文件长度
　　08H 4 char "WAVE"标志
　　0CH 4 char "fmt"标志
　　10H 4 　过渡字节（不定）
　　14H 2 int 格式类别（10H为PCM形式的声音数据)
　　16H 2 int 通道数，单声道为1，双声道为2
　　18H 2 int 采样率（每秒样本数），表示每个通道的播放速度，
　　1CH 4 long int 波形音频数据传送速率，其值为通道数×每秒数据位数×每样本的数据位数／8。播放软件利用此值可以估计缓冲区的大小。
　　20H 2 int 数据块的调整数（按字节算的），其值为通道数×每样本的数据位值／8。播放软件需要一次处理多个该值大小的字节数据，以便将其值用于缓冲区的调整。
　　22H 2 　每样本的数据位数，表示每个声道中各个样本的数据位数。如果有多个声道，对每个声道而言，样本大小都一样。
　　24H 4 char 数据标记符＂data＂
　　28H 4 long int 语音数据的长度
　　PCM数据的存放方式：
　　样本1 样本2
　　8位单声道 0声道 0声道
　　8位立体声 0声道（左） 1声道（右） 0声道（左） 1声道（右）
　　16位单声道 0声道低字节 0声道高字节 0声道低字节 0声道高字节
　　16位立体声 0声道（左）低字节 0声道（左）高字节 1声道（右）低字节 1声道（右）高字节
　　WAVE文件的每个样本值包含在一个整数i中，i的长度为容纳指定样本长度所需的最小字节数。
首先存储低有效字节，表示样本幅度的位放在i的高有效位上，剩下的位置为0，这样8位和16位的PCM波形样本的数据格式如下所示。　
　　样本大小数据格式最大值最小值
　　8位PCM unsigned int 225 0

　　16位PCM int 32767 -32767

2. FFMPEG解复用、解码测试，保存WAV音频文件和PPM图像文件，字幕的处理与保存未做完。

代码如下：

/*************************************************************************************

** Notice:
Copyright (c) 2011 AVIT Corporation - All Rights Reserved

**

** Name:
example.c

**

** Author:
Tang Qi

**

** Date:
2011-08-02

**

** Version:
1.0

**

** Description: The example is use ffmepg to Demux Video Files.We can prove the result

**
of demux is right.

**

** History:
2011-08-02 Tang Qi Created

**

*************************************************************************************/

#include <libavcodec/avcodec.h>

#include <libavformat/avformat.h>

#include <libswscale/swscale.h>

#include <stdio.h>

#include <pthread.h>

/* May be follow header file don't need */

#include <stdlib.h>

#include <time.h>

#define MAX_SAVE_FRAME 40

#define MAX_AUDIO_BUF 20000000

/* 定义全局变量 */

pthread_mutex_t mutex;

pthread_cond_t cond;

int quit = 0;

/* Define DWORD and WORD */

typedef unsigned long DWORD;
/* 4 Bytes */

typedef unsigned short WORD;
/* 2 Bytes */

/* The struct of wave header */

/* ------------------------- */

typedef struct RIFF_HEADER{

char
avit_szRiffID[4];
/* char = "RIFF" */

DWORD
avit_dwRiffSize;
/* filesize - 8 */

char
avit_szRiffFormat[4]; /*char = "WAVE" */

}RIFF_HEADER;

typedef struct WAVE_FORMAT{

char
avit_szWaveID[4];
/* char = "fmt" */

DWORD avit_dwFSize;/* 过渡字节 Ox10 */

WORD
avit_wFormaTag;
/* 编码格式，包括WAVE_FORMAT_PCM，WAVEFORMAT_ADPCM等 */

WORD
avit_wChannels;
/* 声道数，单声道为1，双声道为2 */

DWORD avit_dwSamplesPerSec;
/* 采样频率 */

DWORD avit_dwAvgBytesPerSec; /* 每秒的数据量 */

WORD
avit_wBlockAlign;
/* 块对齐 */

WORD
avit_wBitsPerSample;
/* WAVE文件的采样大小 */

//WORD
sbSize;
/* PCM中忽略此值 */

}WAVE_FORMAT;

typedef struct DATA_BLOCK{

char avit_szDataID[4];
/* char = "data" */

DWORD avit_dwDataSize;/* datasize = filesize - 44 */

}DATA_BLOCK;

/* The struct of PacketQueue is used to save packet. */

/* ------------------------------------------------- */

typedef struct PacketQueue {

AVPacketList *first_pkt, *last_pkt;

int nb_packets;

int size;

} PacketQueue;

/* define audio and video PacketQueue*/

PacketQueue audioq;

PacketQueue videoq;

PacketQueue subtitleq;

/* The handle of packet queue */

/* -------------------------- */

void packet_queue_init(PacketQueue *q)


memset(q, 0, sizeof(PacketQueue));


pthread_mutex_init (&mutex, NULL);//create mutex


pthread_cond_init (&cond, PTHREAD_PROCESS_PRIVATE);//create cond

int packet_queue_put(PacketQueue *q, AVPacket *pkt)


AVPacketList *pkt1;


if(av_dup_packet(pkt) < 0) {


return -1;


pkt1 = av_malloc(sizeof(AVPacketList));


if (!pkt1)


return -1;


pkt1->pkt = *pkt;


pkt1->next = NULL;


pthread_mutex_lock(&mutex);


if (!q->last_pkt)


q->first_pkt = pkt1;


else


q->last_pkt->next = pkt1;


q->last_pkt = pkt1;


q->nb_packets++;


q->size += pkt1->pkt.size;


pthread_cond_signal(&cond);


pthread_mutex_unlock(&mutex);


return 0;

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block)


AVPacketList *pkt1;


int ret;


pthread_mutex_lock(&mutex);


for(;;) {


if(quit) {


ret = -1;


break;


pkt1 = q->first_pkt;


if (pkt1) {


q->first_pkt = pkt1->next;


if (!q->first_pkt)


q->last_pkt = NULL;


q->nb_packets--;


q->size -= pkt1->pkt.size;


*pkt = pkt1->pkt;


av_free(pkt1);


ret = 1;


break;


} else if (!block) {


ret = 0;


break;


} else {


pthread_cond_signal(&cond);


pthread_mutex_unlock(&mutex);


return ret;

void save_video_frame(AVFrame *pFrame, int width, int height, int iFrame)


FILE *frameFile;


char szFilename[32];


int
h;


/* Create file name and open file */


sprintf(szFilename, "frame%d.ppm", iFrame);


frameFile=fopen(szFilename, "wb");


if(frameFile==NULL)


return;


/* Write frameFile header */


fprintf(frameFile, "P6n%d %dn255n", width, height);


/* Write pixel data */


for(h=0; h<height; h++)


fwrite(pFrame->data[0]+h*pFrame->linesize[0], 1, width*3, frameFile);


/* Close the frameFile */


fclose(frameFile);

return;

void video_thread(AVCodecContext *pCodecCtx)


AVPacket pkt1, *packet = &pkt1;


int len1, frameFlag, numBytes, i;


AVFrame *pFrame, *pFrameRGB;


uint8_t *buffer;


printf("EC: video_thread Inn");


i = 0;


pFrame = avcodec_alloc_frame();


/* Alloc buffer to pFrameRGB */


if((pFrameRGB = avcodec_alloc_frame()) == NULL)


return;


/* Determine required buffer size and allocate buffer */


numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,pCodecCtx->height);


buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));


avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,pCodecCtx->width, pCodecCtx->height);


for(;;) {


if(packet_queue_get(&videoq, packet, 1) < 0) {


break; //quit getting packets


/* Decode video frame */


len1 = avcodec_decode_video2(pCodecCtx, pFrame, &frameFlag, packet);


/* Did we get a video frame? */


if(frameFlag) {


/* Convert the image from its native format to RGB */


struct SwsContext *img_convert_ctx;


img_convert_ctx = sws_getContext(pCodecCtx->width,pCodecCtx->height,pCodecCtx->pix_fmt,


pCodecCtx->width,pCodecCtx->height,PIX_FMT_RGB24,


SWS_BICUBIC, NULL,NULL,NULL);


sws_scale(img_convert_ctx,pFrame->data,pFrame->linesize,0,


pCodecCtx->height,pFrame->data,pFrameRGB->linesize);


/* Save the frame to disk */


if(++i <= MAX_SAVE_FRAME)


save_video_frame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, i);


av_free_packet(packet);


av_free(buffer);


av_free(pFrameRGB);


av_free(pFrame);


return ;

void write_wave_header(AVCodecContext *aCodecCtx, FILE *pFile, int filesize)


/* Add Header into the file which is fill up pcm data，and make this file can play */


/* Write header from the beginning of file */


fseek(pFile, 0, SEEK_SET);


RIFF_HEADER riffHeader;


memcpy(riffHeader.avit_szRiffID, "RIFF", 4);// 1-4 byte


riffHeader.avit_dwRiffSize = filesize - 8;


memcpy(riffHeader.avit_szRiffFormat, "WAVE", 4);


fwrite(&riffHeader, 1, sizeof(riffHeader), pFile);


/* Write waveformat */


WAVE_FORMAT waveFormat;


aCodecCtx->bits_per_coded_sample = 16;/*这个值未找到，AVCodecContext中没有。需自己定义?*/


memcpy(waveFormat.avit_szWaveID, "fmt ", 4);


waveFormat.avit_dwFSize = 0x10;


waveFormat.avit_wFormaTag = 1;


waveFormat.avit_wChannels = aCodecCtx->channels;


waveFormat.avit_dwSamplesPerSec = aCodecCtx-> sample_rate;/* 44100、22050、48000HZ */


waveFormat.avit_wBlockAlign = (aCodecCtx->bits_per_coded_sample)/8 * waveFormat.avit_wChannels;


waveFormat.avit_dwAvgBytesPerSec = waveFormat.avit_dwSamplesPerSec * waveFormat.avit_wBlockAlign;


waveFormat.avit_wBitsPerSample = aCodecCtx->bits_per_coded_sample;


fwrite(&waveFormat, 1, sizeof(waveFormat), pFile);


printf("channels = %d, sample_rate = %d, BlockAlign = %d, BytesPerSec = %d, BitsPerSample = %dn",


waveFormat.avit_wChannels,waveFormat.avit_dwSamplesPerSec,waveFormat.avit_wBlockAlign,


waveFormat.avit_dwAvgBytesPerSec,waveFormat.avit_wBitsPerSample );


/* Data Block */


DATA_BLOCK datablock;


memcpy(datablock.avit_szDataID, "data", 4);


datablock.avit_dwDataSize = filesize - 44; // 41-44 byte,calculated


fwrite(&datablock, 1, sizeof(datablock), pFile);


printf("EC:audio_thread(), THe len of the PCM File is %d,End of the audio_decoden", filesize);


fclose(pFile);


return;

/* Read packet from PakcetQueue,and decode audio data */

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf, int buf_size)


static AVPacket pkt,pkt_temp;


static uint8_t *audio_pkt_data = NULL;


static int audio_pkt_size = 0;


int len1, data_size;


for(;;) {


while(pkt_temp.size > 0) {


data_size = buf_size;


len1 = avcodec_decode_audio3(aCodecCtx, (int16_t *)audio_buf, &data_size, &pkt_temp);/* avcodec_decode_audio2() too old, change to avcodec_decode_audio3() */


if(len1 < 0) {


/* if error, skip this frame */


pkt_temp.size = 0;


break;


pkt_temp.data += len1;


pkt_temp.size
-= len1;


if(data_size <= 0) {


/* No data yet, get more frames */

	continue;


/* We have data, return it and come back for more later */


return data_size;


/* free the current packet */


if(pkt.data)


av_free_packet(&pkt);

/*


if(quit) {


return -1;

}*/


/* read next packet from audio PacketQueue */


if(packet_queue_get(&audioq, &pkt, 1) < 0) {


return -1;


pkt_temp.data = pkt.data;


pkt_temp.size
= pkt.size;

void audio_thread(AVCodecContext *aCodecCtx)


int len1, audio_size, len, ture,filesize,n;


static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];


static unsigned int audio_buf_size = 0;


static unsigned int audio_buf_index = 0;


len = MAX_AUDIO_BUF;


n = 1;


/* Creat and open a File */


FILE *pFile;


char filename[32];


sprintf(filename, "test%d.wav", n);


pFile = fopen(filename, "wb");


/* AT 44 bytes pointer, write data to pFile */


fseek(pFile, 44, SEEK_SET);


filesize = 44;


//ture = 1;


/* decode audio frame */


while(len > 0) {


if(audio_buf_index >= audio_buf_size) {


/* We have already sent all our data; get more */


audio_size = audio_decode_frame(aCodecCtx, audio_buf, sizeof(audio_buf));


/* Save audio_buf to the PCM File. */


if(audio_size> 0){



fwrite(audio_buf, 1, audio_size, pFile);



filesize += audio_size;



printf("EC: audio_thread() THe len of the PCM File is %dn", filesize);


if(audio_size < 0) {


/* If error, output silence */


audio_buf_size = 1024; // arbitrary?


memset(audio_buf, 0, audio_buf_size);


printf("EC: audio_thread() *****Output silence *****n" );


} else {


audio_buf_size = audio_size;


audio_buf_index = 0;


len1 = audio_buf_size - audio_buf_index;


if(len1 > len)


len1 = len;


printf("EC: audio_thread(), audio_size = %d, audio_buf_size = %d, audio_buf_index = %d, len = %d, len1 = %dn",

	audio_size, audio_buf_size, audio_buf_index, len, len1);


// memcpy(stream, (uint8_t *)audio_buf + audio_buf_index, len1);


//stream += len1;


len -= len1;


audio_buf_index += len1;


/* write wave header to this file*/


write_wave_header(aCodecCtx, pFile, filesize);


return;

void subtitle_thread(AVCodecContext *sCodecCtx)


SubPicture *sp;


AVPacket pkt1, *pkt = &pkt1;


int len1, got_subtitle;


int i;

FILE *textFile;

char filename[32];

int text_id = 1;

sprintf(filename, "subtitle%d.txt", text_id);

textFile = fopen(filename, "wb");


for(;;) {


if (packet_queue_get(&subtitleq, pkt, 1) < 0)


break;


len1 = avcodec_decode_subtitle2(sCodecCtx, &sp->sub, &got_subtitle, pkt);

if (got_subtitle && len1 > 0){

printf("EC: subtitle_thread() sub.format = %d, len1 = %dn", sp->sub.format, len1);

for(i = 0; i < sp->sub.num_rects; i++){

switch(sp->sub.rects[i]->type){

case SUBTITLE_TEXT:

printf("EC: subtitle() Enter in save SUBTITLE_TEXTn");

fwrite(sp->sub.rects[i]->text, 1, sizeof(sp->sub.rects[i]->text), textFile);

break;

case SUBTITLE_ASS:

printf("EC: subtitle() Enter in save SUBTITLE_ASSn");

break;

case SUBTITLE_BITMAP:

printf("EC: subtitle() Enter in save SUBTITLE_BITMAPn");

break;

default:

printf("EC: subtitle() Enter in save SUBTITLE_NONEn");

break;


av_free_packet(pkt);

return;

void avit_decode(AVFormatContext *pFormatCtx, AVCodecContext *pCodecCtx,

AVCodecContext *aCodecCtx, AVCodecContext * sCodecCtx,int subtitle_flag)

pthread_t audio_id;

pthread_t video_id;

pthread_t subtitle_id;

/* Create video decode thread */

if(pthread_create(&video_id, NULL, (void *)video_thread, pCodecCtx) != 0)

printf("Create video thread failure!n");

/* Create audio decode thread */

if(pthread_create(&audio_id, NULL, (void *)audio_thread, aCodecCtx) != 0)

printf("Create audio thread failure!n");

/* Create subtitle decode thread */

if(subtitle_flag != -1){

if(pthread_create(&subtitle_id, NULL, (void *)subtitle_thread, sCodecCtx) != 0 )

printf("Create subtitle thread failure!n");

return;

int main(int argc, char *argv[])


int i, videoStream, audioStream, subtitleStream, frameFinished;

AVFormatContext *pFormatCtx;

AVCodecContext *pCodecCtx, *aCodecCtx, *sCodecCtx;


AVCodec
*pCodec, *aCodec, *sCodec;

AVPacket
packet;


if(argc < 2) {


fprintf(stderr, "Usage: test <file>n");


exit(1);


/* Register all formats and codecs */


av_register_all();

/* Init audio PacketQueue and video PacketQueue.*/

packet_queue_init(&audioq);


packet_queue_init(&videoq);

packet_queue_init(&subtitleq)


/* Open video file */


if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0){

printf("Couldn't open this file,Please provide another one!n");


return -1; // Couldn't open this file


/* Find stream information */


if(av_find_stream_info(pFormatCtx)<0){

printf("Couldn't find stream information from file!n");


return -1; // Couldn't find stream information


/* Dump information about file onto standard error */


dump_format(pFormatCtx, 0, argv[1], 0);


/* Find the first video and audio stream */


videoStream = -1;


audioStream = -1;

subtitleStream = -1;


for(i = 0; i < pFormatCtx->nb_streams; i++) {


if(pFormatCtx->streams[i]->codec->codec_type == CODEC_TYPE_VIDEO && videoStream < 0)


videoStream = i;


else if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_AUDIO && audioStream < 0)


audioStream = i;

else (pFormatCtx->streams[i]->codec->codec_type == CODEC_TYPE_SUBTITLE && subtitleStream < 0)

subtitleStream = i;

if(videoStream == -1){

printf("Couldn't fine a video stream!n");

return -1;


if(audioStream == -1){

printf("Couldn't find a audio stream!n");

return -1;

if(subtitleStream == -1){

printf("Couldn't find a subtitle Stream!n");

//Don't return -1,we play this file whithout subtitle.


/* Get a pointer to the codec context for the video stream, and open ths video codec. */


pCodecCtx=pFormatCtx->streams[videoStream]->codec;


if((pCodec = avcodec_find_decoder(pCodecCtx->codec_id)) == NULL){

printf("Unsupported pCodec, please provide another video file!n");

return -1;


if(avcodec_open(pCodecCtx, pCodec) < 0){

printf("Couldn't open video codec!n");


return -1;

/* Get a pointer to the codec context for the audio stream, and open the audio codec. */

aCodecCtx=pFormatCtx->streams[audioStream]->codec;


if((aCodec = avcodec_find_decoder(aCodecCtx->codec_id)) == NULL){


printf("Unsupported aCodec, please provide another video file!n");


return -1;


if(avcodec_open(aCodecCtx, aCodec) <0 ){

printf("Couldn't open aucio codec!n");// Don't return -1, play the video file whit silence.

return -1;

/* Get a pointer to the codec context for the subtitle stream, and open the subtitle codec. */

sCodecCtx = pFormatCtx->streams[subtitleStream]->codec;

if((sCodec = avcodec_find_decoder(aCodecCtx->codec_id)) == NULL){

prinft("Unsupperted sCodec, we will not decode subtitle stream!n");

//Don't return -1, we play thie file whithout subtitle.

if(avcodec_open(sCodecCtx, sCodec) < 0){

printf("Couldn't open subtitle codec!n");

/* Enter into decode function,it create decode thread */

avit_decode(pFormatCtx, aCodecCtx, pCodecCtx,sCodecCtx, subtitleStream);


/* Read frame into packet and put the packet into PacketQueues */


while(av_read_frame(pFormatCtx, &packet)>=0) {

switch(packet.stream_index){

case videoStream:

packet_queue_put(&videoq, &packet);

break;

case audioStream:

packet_queue_put(&audioq, &packet);

break;

case subtitleStream:

packet_queue_put(&subtitleq, &packet);

break;

default:

av_free_packet(&packet);

break;

/* When read
packet to the QueuePacket Finish, wait for decode finish.*/

/* Wait for thread finished */

/* ------------------------ */

sleep(60);

quit = 1;

// Close the codec


avcodec_close(pCodecCtx);


avcodec_close(aCodecCtx);

avcodec_close(sCodecCtx);


av_close_input_file(pFormatCtx);


return 0;

最后

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本文分类：FFMPEG
浏览次数：53 次浏览
发布日期：2023-11-28 08:35:07
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FFMPEG解复用、解码测试，音频保存WAV文件，视频保存为PPM图像1. WAV(PCM)文件格式分析

概述

1. WAV(PCM)文件格式分析

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FFMPEG解复用、解码测试，音频保存WAV文件，视频保存为PPM图像1. WAV(PCM)文件格式分析

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1. WAV(PCM)文件格式分析

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