fix noise problem

simplest_audio_play_sdl2/simplest_audio_play_sdl2.cpp

@@ -17,9 +17,9 @@
  * [初始化]
  * SDL_Init(): 初始化SDL。
  * SDL_OpenAudio(): 根据参数（存储于SDL_AudioSpec）打开音频设备。
+ * SDL_PauseAudio(): 播放音频数据。
  *
  * [循环播放数据]
- * SDL_PauseAudio(): 播放音频数据。
  * SDL_Delay(): 延时等待播放完成。
  *
  * This software plays PCM raw audio data using SDL2.
@@ -32,9 +32,9 @@
  * SDL_Init(): Init SDL.
  * SDL_OpenAudio(): Opens the audio device with the desired 
  *					parameters (In SDL_AudioSpec).
+ * SDL_PauseAudio(): Play Audio.
  *
  * [Loop to play data]
- * SDL_PauseAudio(): Play Audio.
  * SDL_Delay(): Wait for completetion of playback.
  */
 
@@ -97,11 +97,14 @@ int main(int argc, char* argv[])
 		printf("cannot open this file\n");
 		return -1;
 	}
-	//For YUV420P
+
 	int pcm_buffer_size=4096;
 	char *pcm_buffer=(char *)malloc(pcm_buffer_size);
 	int data_count=0;
 
+	//Play
+	SDL_PauseAudio(0);
+
 	while(1){
 		if (fread(pcm_buffer, 1, pcm_buffer_size, fp) != pcm_buffer_size){
 			// Loop
@@ -116,8 +119,7 @@ int main(int argc, char* argv[])
 		//Audio buffer length
 		audio_len =pcm_buffer_size;
 		audio_pos = audio_chunk;
-		//Play
-		SDL_PauseAudio(0);
+
 		while(audio_len>0)//Wait until finish
 			SDL_Delay(1); 
 	}

simplest_ffmpeg_audio_player/simplest_ffmpeg_audio_player.cpp

@@ -81,8 +81,9 @@ static  Uint8  *audio_pos;
 void  fill_audio(void *udata,Uint8 *stream,int len){ 
 	//SDL 2.0
 	SDL_memset(stream, 0, len);
-	if(audio_len==0)		/*  Only  play  if  we  have  data  left  */ 
-			return; 
+	if(audio_len==0)
+		return; 
+
 	len=(len>audio_len?audio_len:len);	/*  Mix  as  much  data  as  possible  */ 
 
 	SDL_MixAudio(stream,audio_pos,len,SDL_MIX_MAXVOLUME);
@@ -110,7 +111,7 @@ int main(int argc, char* argv[])
 	struct SwrContext *au_convert_ctx;
 
 	FILE *pFile=NULL;
-	char url[]="WavinFlag.aac";
+	char url[]="xiaoqingge.mp3";
 
 	av_register_all();
 	avformat_network_init();
@@ -208,6 +209,9 @@ int main(int argc, char* argv[])
 		in_channel_layout,pCodecCtx->sample_fmt , pCodecCtx->sample_rate,0, NULL);
 	swr_init(au_convert_ctx);
 
+	//Play
+	SDL_PauseAudio(0);
+
 	while(av_read_frame(pFormatCtx, packet)>=0){
 		if(packet->stream_index==audioStream){
 			ret = avcodec_decode_audio4( pCodecCtx, pFrame,&got_picture, packet);
@@ -239,8 +243,6 @@ int main(int argc, char* argv[])
 			audio_len =out_buffer_size;
 			audio_pos = audio_chunk;
 
-			//Play
-			SDL_PauseAudio(0);
 #endif
 		}
 		av_free_packet(packet);
@@ -252,14 +254,12 @@ int main(int argc, char* argv[])
 	SDL_CloseAudio();//Close SDL
 	SDL_Quit();
 #endif
-	// Close file
+
 #if OUTPUT_PCM
 	fclose(pFile);
 #endif
 	av_free(out_buffer);
-	// Close the codec
 	avcodec_close(pCodecCtx);
-	// Close the video file
 	avformat_close_input(&pFormatCtx);
 
 	return 0;