ffmpeg + sdl -03 简单音频播放器实现

没办法，工作中遇到了问题。

目前NEC EMMA的架构如下：

从USB读入文件 -> 文件分析并提取Packet中的Payload Data -> NEC HANDLE AVTransfer -> NEC HANDLE WMV -> AUDIO OUTPUT

按照驱动的API写好代码后却怎么也没有声音，所有API返回值均OK。

郁闷开始了。继续绝望中寻找希望。

为了对比调试，参考

http://blog.csdn.net/ashlingr/article/details/7791321

并做了一些ffmpeg版本升级修改。

修改前：

 len=avcodec_decode_audio(pAudioCodecCtx,
 (int16_t*)decompressed_audio_buf,
 &decompressed_audio_buf_size,//itisthedecompressedframeinBYTES解码后的数据大小，字节为单位；
 packet.data,
 packet.size);

修改后：

decompressed_audio_buf_size = (AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2; // 不加这一行，执行时会出错。

len = avcodec_decode_audio3 (pCodecCtx,

(int16_t *)decompressed_audio_buf,

&decompressed_audio_buf_size, // it is the decompressed frame in BYTES

&packet);

遇到的问题：

/dev/dsp 设备不存在

解决办法：

modprobe snd_pcm_oss （需要su到root用户）

完整代码如下：（基本来自http://bbs.chinavideo.org/viewthread.php?tid=1247&extra=page%3D1）

#include <avcodec.h>
#include <avformat.h>
#include <avutil.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include <sys/soundcard.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sched.h>


#define ALL_DEBUG


#ifdef ALL_DEBUG
#define AV_DEBUG
#define AUDIO_DEBUG
#endif


//------------------------------------------------------------------------------
// manipulations for file
int open_file (char *file_name, int mode)
{
// open file file_name and return the file descriptor;
int fd;


if ((fd = open (file_name, mode)) < 0)
{
fprintf (stderr, " Can't open %s!/n", file_name);
exit (-1);
}
return fd;
}


int set_audio (int fd, AVCodecContext * pCodecCtx)
{
// set the properties of audio device with pCodecCtx;


int i, err;
/* 设置适当的参数，使得声音设备工作正常 */
/* 详细情况请参考Linux关于声卡编程的文档 */

i = 0;
ioctl (fd, SNDCTL_DSP_RESET, &i);
i = 0;
ioctl (fd, SNDCTL_DSP_SYNC, &i);
i = 1;
ioctl (fd, SNDCTL_DSP_NONBLOCK, &i);

// set sample rate;
#ifdef AUDIO_DEBUG
printf ("pCodecCtx->sample_rate:%d/n", pCodecCtx->sample_rate);
#endif
i = pCodecCtx->sample_rate;
if (ioctl (fd, SNDCTL_DSP_SPEED, &i) == -1)
{
fprintf (stderr, "Set speed to %d failed:%s/n", i,
strerror (errno));
return (-1);
}
if (i != pCodecCtx->sample_rate)
{
fprintf (stderr, "do not support speed %d,supported is %d/n",
pCodecCtx->sample_rate, i);
return (-1);
}

// set channels;
i = pCodecCtx->channels;
#ifdef AUDIO_DEBUG
printf ("pCodecCtx->channels:%d/n", pCodecCtx->channels);
#endif
if ((ioctl (fd, SNDCTL_DSP_CHANNELS, &i)) == -1)
{
fprintf (stderr, "Set Audio Channels %d failed:%s/n", i,
strerror (errno));
return (-1);
}
if (i != pCodecCtx->channels)
{
fprintf (stderr, "do not support channel %d,supported %d/n",
pCodecCtx->channels, i);
return (-1);
}
// set bit format;
i = AFMT_S16_LE;
if (ioctl (fd, SNDCTL_DSP_SETFMT, &i) == -1)
{
fprintf (stderr, "Set fmt to bit %d failed:%s/n", i,
strerror (errno));
return (-1);
}
if (i != AFMT_S16_LE)
{
fprintf (stderr, "do not support bit %d, supported %d/n",
AFMT_S16_LE, i);
return (-1);
}

// set application buffer size;
// i = (0x00032 << 16) + 0x000c; // 32 4kb buffer;
// ioctl (fd, SNDCTL_DSP_SETFRAGMENT, &i);
i = 1;
ioctl (fd, SNDCTL_DSP_PROFILE, &i);

return 0;
}


void close_file (int fd)
{
// close the file pointed by file descriptor fd;
close (fd);
}


//------------------------------------------------------------------------------
// handle audio;


void display_AVCodecContext(AVCodecContext *pCodecCtx){
//
#define STDOUT stderr
fprintf(STDOUT, "pCodecCtx->bit_rate:%d/n", pCodecCtx->bit_rate);
fprintf(STDOUT, "pCodecCtx->sample_rate:%d/n", pCodecCtx->sample_rate);
fprintf(STDOUT, "pCodecCtx->channels:%d/n", pCodecCtx->channels);
fprintf(STDOUT, "pCodecCtx->frame_size:%d/n", pCodecCtx->frame_size);
fprintf(STDOUT, "pCodecCtx->frame_number:%d/n", pCodecCtx->frame_number);
fprintf(STDOUT, "pCodecCtx->delay:%d/n", pCodecCtx->delay);
fprintf(STDOUT, "pCodecCtx->frame_bits:%d/n", pCodecCtx->frame_bits);
}


// error if return -1;
// success if return 0;
// 这里要用到指向指针的指针，否则传不到值；
int av_init (char *file_name, AVFormatContext ** pFormatCtx,
AVCodecContext ** pCodecCtx, int *p_audioStream)
{
// init the codec and format of input file file_name;
int audioStream, i;
AVCodec *pCodec;
// catch error
assert(file_name != NULL);
assert(*pFormatCtx != NULL);
assert(*pCodecCtx != NULL);

// Register all formats and codecs
av_register_all ();

// open file
if (av_open_input_file (pFormatCtx, file_name, NULL, 0, NULL) != 0){
// Couldn't open file
fprintf (stderr, " Can't open %s!/n", file_name);
return -1;
}


// Retrieve stream information
if (av_find_stream_info (*pFormatCtx) < 0){
// Couldn't find stream information
return -1;
}

#ifdef AV_DEBUG
// Dump information about file onto standard error
dump_format (*pFormatCtx, 0, file_name, 0);
#endif

// Find the first audio and video stream respectively
audioStream = -1;
for (i = 0; i < (*pFormatCtx)->nb_streams; i++){
if ((*pFormatCtx)->streams[i]->codec->codec_type ==
AVMEDIA_TYPE_AUDIO)
{
audioStream = i;
}
}

#ifdef AV_DEBUG
// dump_stream_info(pFormatCtx);
#endif

// exclude error
if (audioStream == -1){
// Didn't find a audio or video stream
return -1;
}


// Get a pointer to the codec context for the audio stream
*pCodecCtx = (*pFormatCtx)->streams[audioStream]->codec;


// Find the decoder for the audio stream
pCodec = avcodec_find_decoder ((*pCodecCtx)->codec_id);
if (pCodec == NULL)
return -1; // Codec not found


// Open codec
if (avcodec_open ((*pCodecCtx), pCodec) < 0){
return -1; // Could not open codec
}

#ifdef AUDIO_DEBUG
// printf ("pCodecCtx->sample_rate:%d, audioStream:%d/n", (*pCodecCtx)->sample_rate, audioStream);
// display_AVCodecContext(*pCodecCtx);
#endif

*p_audioStream = audioStream;

return 0;
}


void av_play (AVFormatContext * pFormatCtx,
AVCodecContext * pCodecCtx, int audioStream)
{
// which was read from one frame;
AVPacket packet;
uint32_t len;
uint8_t decompressed_audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
int decompressed_audio_buf_size;
uint8_t * p_decompressed_audio_buf;
int fd = -1; // audio file or test file?
char filename[64] = "/dev/dsp";
int mode = O_WRONLY;
//

// open audio file or written file
// printf("fd:%d", fd);
fd = open_file(filename, mode);
printf("fd:%d \n", fd);
//
set_audio(fd, pCodecCtx);

//
printf("(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2=%d\n", (AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2);
printf("AVCODEC_MAX_AUDIO_FRAME_SIZE=%d\n", AVCODEC_MAX_AUDIO_FRAME_SIZE);

// for a test
// char test_file[256] = "my_pcm.pcm";
// fd = open_file(test_file, mode);

#ifdef AV_DEBUG
static int size = 0;
#endif
//

// set the sched priority
// 这是为了提高音频优先级；不晓得起作用没；
int policy = SCHED_FIFO;
sched_setscheduler(0, policy, NULL);

int write_buf_size = 4196;
int written_size;
while (av_read_frame (pFormatCtx, &packet) >= 0)
{
// Is this a packet from the audio stream?
// 判断是否音频帧；
if (packet.stream_index == audioStream)
{
// Decode audio frame
// 解码音频数据为pcm数据；
decompressed_audio_buf_size = (AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2;
len = avcodec_decode_audio3 (pCodecCtx,
(int16_t *)decompressed_audio_buf,
&decompressed_audio_buf_size, // it is the decompressed frame in BYTES
&packet);
// printf("len:%d, packet.size:%d/n", len, packet.size);
if ( len < 0 ){
// if error len = -1
printf("+----- error in decoding audio frame\n");
// exit(0);
}
// test lsosa


// printf("size = %d/n", size);
//******************************************************************
// 重点是这一部分，使用oss播放的代码，之前的数据写是否完整的问题就是出在这里，或者是前面的set_audio函数设置不正确；
// audio_buf_info info;
p_decompressed_audio_buf = decompressed_audio_buf;
while ( decompressed_audio_buf_size > 0 ){
// 解码后数据不为零，则播放之，为零，则；
written_size = write(fd, p_decompressed_audio_buf, decompressed_audio_buf_size);
if ( written_size == -1 ){
// printf("error:decompressed_audio_buf_size:%d, decompressed_audio_buf_size:%d, %s/n", /
// decompressed_audio_buf_size, decompressed_audio_buf_size,strerror(errno));
// usleep(100);
continue;
}
// printf("decompressed_audio_buf_size:%d, written_size:%d/n", /
// decompressed_audio_buf_size, written_size);
decompressed_audio_buf_size -= written_size;
p_decompressed_audio_buf += written_size;

}// end while
//******************************************************************
}
else
{
printf("+----- this is not audio frame/n");
}// end if
// Free the packet that was allocated by av_read_frame
av_free_packet (&packet);
}// end while of reading one frame;

close_file(fd);
}


void av_close (AVFormatContext * pFormatCtx, AVCodecContext * pCodecCtx)
{
// close the file and codec


// Close the codec
avcodec_close (pCodecCtx);


// Close the video file
av_close_input_file (pFormatCtx);
}


//------------------------------------------------------------------------------


int main (int argc, char **argv){
//
AVFormatContext *pFormatCtx;
int audioStream = -1;
AVCodecContext *pCodecCtx;

// exclude the error about args;
if ( argc != 2 ){
printf("please give a file name\n");
exit(0);
}

// 注意：这里要用到指向指针的指针，是因为这个初始化函数需要对指针的地址进行改动，
// 所以，只有这么做，才能达到目的；
if ( av_init(argv[1], &pFormatCtx, &pCodecCtx, &audioStream) < 0 ){
//
fprintf(stderr, "error when av_init\n");
}

// play the audio file
av_play(pFormatCtx, pCodecCtx, audioStream);

// close all the opend files
av_close(pFormatCtx, pCodecCtx);

}