ffmpeg tutorial 3 教程結果分析 · FFmpeg入門實踐與分析

目標：關注聲音回調函數與聲音解碼函數的關系關注視頻幀調用過程未完成測試案列：測試平臺：測試代碼：首先來說，為什么可以出聲音，我認為是這個函數 SDL_pauseAudio 的行為. ### 關注聲音回調函數與解碼的關系用數據來說話，分別在兩個位置下斷點位置一是：audio_callback函數位置位置二是：audio_decode_frame解碼函數位置讓我們來看看實際的代碼： ~~~ void audio_callback(void *userdata, Uint8 *stream, int len) { AVCodecContext *aCodecCtx = (AVCodecContext *)userdata; int len1, audio_size; static uint8_t audio_buf[(MAX_AUDIO_FRAME_SIZE * 3) / 2]; static unsigned int audio_buf_size = 0; static unsigned int audio_buf_index = 0; 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, audio_buf_size);//請特別注意。 ~~~ ~~~ if(audio_size < 0) { /* If error, output silence */ audio_buf_size = 1024; // arbitrary? memset(audio_buf, 0, audio_buf_size); } else { audio_buf_size = audio_size; } audio_buf_index = 0; } ~~~ ~~~ len1 = audio_buf_size - audio_buf_index; if(len1 > len) len1 = len; memcpy(stream, (uint8_t *)audio_buf + audio_buf_index, len1); len -= len1; stream += len1; audio_buf_index += len1; } } ~~~ 結果如下，可以看到至少4次audio_decode_frame后，系統將會調用回調函數。這樣的回調會周期性發生。有同學會問，為什么是4次？我想要么是給系統回調的聲音buffer放滿了，要么是audio_callback 定時調用。 ~~~ Function: audio_callback(void *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_callback(void *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_callback(void *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_callback(void *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_callback(void *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 Function: audio_decode_frame(AVCodecContext *, unsigned char *, int), Thread: 0x81B8 Win32 線程 ~~~ ### 關注視頻幀調用過程之所以貼在這里，想以后再分析，再給出結果。理論上，12個時刻，應該對應12個不同的幀，但是結果不是，看看以下結果（用notepad++處理后，用于統計個數）。 ~~~ Search "video" (11 hits in 1 file) new 2 (11 hits) Line 120: read one video frame Line 286: read one video frame Line 291: read one video frame Line 292: read one video frame Line 293: read one video frame Line 294: read one video frame Line 295: read one video frame Line 296: read one video frame Line 297: read one video frame Line 298: read one video frame Line 299: read one video frame Search "audio" (288 hits in 1 file) ~~~ ###未完成其他：看看第一次調用audio_callback時，是否遇到返回為空的情形。其他：請打印出每次解碼出的buffer大小，尤其注意那個中間連續調用五次解碼的過程。其他：是否可以結合dump出的文件信息，量化分析過程。