ffmpeg如何从内存读取h264音视频流进行解码显示

由于项目组重组，自己有幸开始做音视频编解码方面的研发工作，现将自己近期的工作收获作为BOLG的方式记录起来，方便自己日后查阅和学习。说到H264编解码，不能不提到ffmpeg，据自己查证的资料显示，现大部分软件的H264编解码基本都是使用ffmpeg作为自己的三方库工具，关于ffmpeg有多牛，这里不作赘述。

按照之前查阅的资料，ffmpeg可以解码rtp网络流、从内存读取数据流来解码、读取文件流并解码，本篇幅主要介绍ffmpeg如何从内存读取h264数据流并解码显示，这里只重点关注成功解码h264视频流的关键步骤，关于视频显示与音视叔同步部分将在后续内容继续更新！

  先帖上部分代码:

1. CDecoder::CDecoder()

2. :m_avFmtContext( NULL )

3. ,m_pFrame( NULL )

4. ,m_pCodecCtx( NULL )

5. ,m_bQuit( false )

6. ,m_openTd( NULL )

7. ,m_disPlayTd( NULL )

8. ,m_direcDraw( NULL )

9. {

10. av_register_all();

11. }

12.  

13. CDecoder::~CDecoder()

14. {

15.  

16. }

17.  

18. bool CDecoder::init( void *hwnd )

19. {

20. if ( m_avFmtContext )

21. {

22. avformat_close_input( &m_avFmtContext );

23. m_avFmtContext = NULL;

24. }

25.  

26. if ( !m_avFmtContext )

27. {

28. m_avFmtContext = avformat_alloc_context();

29.  

30. AVCodec* pCodec = avcodec_find_decoder( AV_CODEC_ID_H264 );

31.  

32. if ( pCodec )

33. {

34. av_format_set_video_codec( m_avFmtContext, pCodec );

35.  

36. m_avFmtContext->video_codec_id = AV_CODEC_ID_H264;//AV_CODEC_ID_H264;

37. }

38. }

39.  

40. if ( !m_direcDraw )

41. {

42. m_direcDraw = new CDirectDraw((HWND)hwnd );

43. m_direcDraw->dirrectDrawInit((HWND)hwnd);

44. }

45.  

46. m_bQuit = false;

47. if ( !m_spOpenThread )

48. {

49. m_spOpenThread.reset( new boost::thread( boost::bind( &CDecoder::openStream, this ) ) );

50. }

1. return true;

2. }

3.  

4. void CDecoder::openStream()

5. {

6. uint8_t* pBuf = (uint8_t *)av_mallocz( sizeof(uint8_t) * BUF_SIZE );

7.  

8. m_avFmtContext->pb = avio_alloc_context( pBuf, BUF_SIZE, 0, this, readRawDataCB, NULL, NULL );

9.  

10. if ( !m_avFmtContext->pb )

11. {

12. std::cout << "avio_alloc_context error!" << std::endl;

13.  

14. return;

15. }

16.  

17. // [ 探测流信息，主要来填充AVInputFormat结构体，为下面的打开流IO作准备 ]

18. AVInputFormat *pAvInputFmt = NULL;

19. //AVInputFormat *pAvInputFmt = av_find_input_format("h264");

20. if ( av_probe_input_buffer( m_avFmtContext->pb, &pAvInputFmt, NULL, NULL, 0, 0 ) < 0 )

21. {

22. std::cout << __FUNCTION__ << " : " << __LINE__ << " error! " << std::endl;

23. //avio_close( m_avFmtContext->pb );

24. //av_err2str

25. m_avFmtContext->pb = NULL;

26. return;

27. }

28.  

29. av_init_packet(&m_avpkt);

30.  

31. if ( !m_pFrame )

32. {

33. m_pFrame = av_frame_alloc();

34. }

35.  

36. AVFrame *pFrameRGB = NULL;

37.  

38. // [ 打开流 ]

39. if ( avformat_open_input( &m_avFmtContext, NULL, pAvInputFmt, NULL ) < 0 )

40. {

41. std::cout << "avformat_open_input error!" << std::endl;

42.  

43. return;

44. }

45.  

46. //读取数据

47. int frameFinished = -1;

48. int videoStreamNum = -1;

49. AVCodecContext *pCodecCtx = NULL;

50. AVCodec *pCodec = NULL;

51. static struct SwsContext *img_convert_ctx = NULL;

52. while( true )

53. {

54. if ( m_bQuit )

55. return;

56.  

57. int ret = av_read_frame(m_avFmtContext, &m_avpkt);

58. if ( ret < 0 )

59. {

60. boost::thread::sleep( boost::get_system_time() + boost::posix_time::milliseconds( 10) );

61. continue;

62. }

63.  

64. if ( videoStreamNum == -1 )

65. {

66. // [ 查找是否有视频流 ]

67. for(int i=0; i<(m_avFmtContext->nb_streams); i++)

68. {

69. if(m_avFmtContext->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO) //找出视频流

70. {

71. videoStreamNum=i;

72. break;

73. }

74. }

75.  

76. if(videoStreamNum==-1)

77. return;

78.  

79. // [ 找出解码器信息上下文和AVCodec解码器，用于下面打开解码器和解码AvPacket ]

80.  

81. pCodecCtx = m_avFmtContext->streams[videoStreamNum]->codec;

82.  

83. // 从视频流中找出相应解码器

84. pCodec=avcodec_find_decoder(m_avFmtContext->streams[videoStreamNum]->codec->codec_id);

85. if(pCodec==NULL)

86. {

87. fprintf(stderr, "Unsupported codec!\n");

88. return;

89. }

90.  

91. // [ 打开流信息中查找到流解码器 ]

92. if(avcodec_open2(pCodecCtx, pCodec,NULL)<0)

93. return; // Could not open codec

94.  

95. pCodecCtx->width = 1920;

96. pCodecCtx->height = 1080;

97. pCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;

98.  

99. if ( !pFrameRGB )

100. {

101. pFrameRGB = av_frame_alloc();

102.  

103. if ( !pFrameRGB )

104. return;

105.  

106. pFrameRGB->width = pCodecCtx->width;

107. pFrameRGB->height = pCodecCtx->height;

108. pFrameRGB->format = PIX_FMT_YUV420P;

109.  

110. if ( av_image_alloc( pFrameRGB->data, pFrameRGB->linesize,

111. pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, 1 ) < 0 )

112. {

113. av_frame_free( &pFrameRGB );

114.  

115. pFrameRGB = NULL;

116.  

117. return;

118. }

119. }

120.  

121. img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,

122. pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,

123. PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);

124. }

125.  

126. if(m_avpkt.stream_index==videoStreamNum)

127. {

128. // 解码

129. avcodec_decode_video2( pCodecCtx, m_pFrame, &frameFinished, &m_avpkt );

130.  

131. if ( frameFinished > 0 )

132. {

133. static uint8_t *p = NULL;

134.  

135. p = m_pFrame->data[1];

136. m_pFrame->data[1] = m_pFrame->data[2];

137. m_pFrame->data[2] = p;

138.  

139. sws_scale(img_convert_ctx, m_pFrame->data, m_pFrame->linesize,

140. 0, pCodecCtx->height,pFrameRGB->data,pFrameRGB->linesize);

141.  

142. sPictureSize sPicSize;

143. sPicSize.nHeight = pCodecCtx->height;

144. sPicSize.nWidth = pCodecCtx->width;

145. m_direcDraw->dirrectDrawInputData(pFrameRGB->data[0], sPicSize);

146. m_direcDraw->directDrawUpDateData();

147.  

148. //SaveAsBMP( pFrameRGB, pCodecCtx->width, pCodecCtx->height, 1, 1 );

149. }

150. }

151.  

152. av_free_packet(&m_avpkt);

153. }

154.