Libav AVFrame to Opencv Mat to convert AVPacket

Question

I am new to libav and I am writing video processing software that uses opencv as its heart. What I did is briefly as shown below:

1- read the video package

2- decode packet in AVFrame

3- convert AVFrame to CV Mat

4- manipulate the mat

5- convert CV Mat to AVFrame

6- encode AVFrame in AVPacket

7- write a package

8-goto 1

I read the safety tutorial at http://dranger.com/ffmpeg/tutorial01.html and I also used the decoding_encoding example. I can read videos, extract video frames and convert them to CV Mat. My problem starts with converting from cv Mat to AVFrame and encoding it in AVPacket.

Could you help me with this?

Here is my code:

int main(int argc, char **argv) { AVOutputFormat *ofmt = NULL; AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL; AVPacket pkt; AVCodecContext *pCodecCtx = NULL; AVCodec *pCodec = NULL; AVFrame *pFrame = NULL; AVFrame *pFrameRGB = NULL; int videoStream=-1; int audioStream=-1; int frameFinished; int numBytes; uint8_t *buffer = NULL; struct SwsContext *sws_ctx = NULL; FrameManipulation *mal_frame; const char *in_filename, *out_filename; int ret, i; if (argc < 3) { printf("usage: %s input output\n" "API example program to remux a media file with libavformat and libavcodec.\n" "The output format is guessed according to the file extension.\n" "\n", argv[0]); return 1; } in_filename = arg[1]; out_filename = arg[2]; av_register_all(); if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) { fprintf(stderr, "Could not open input file '%s'", in_filename); goto end; } if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) { fprintf(stderr, "Failed to retrieve input stream information"); goto end; } av_dump_format(ifmt_ctx, 0, in_filename, 0); avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename); if (!ofmt_ctx) { fprintf(stderr, "Could not create output context\n"); ret = AVERROR_UNKNOWN; goto end; } ofmt = ofmt_ctx->oformat; for (i = 0; i < ifmt_ctx->nb_streams; i++) { AVStream *in_stream = ifmt_ctx->streams[i]; AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec); if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO && videoStream < 0) { videoStream=i; } if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO && audioStream < 0) { audioStream=i; } if (!out_stream) { fprintf(stderr, "Failed allocating output stream\n"); ret = AVERROR_UNKNOWN; goto end; } ret = avcodec_copy_context(out_stream->codec, in_stream->codec); if (ret < 0) { fprintf(stderr, "Failed to copy context from input to output stream codec context\n"); goto end; } out_stream->codec->codec_tag = 0; if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER) out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER; } pCodec=avcodec_find_decoder(ifmt_ctx->streams[videoStream]->codec->codec_id); pCodecCtx = avcodec_alloc_context3(pCodec); if(avcodec_copy_context(pCodecCtx, ifmt_ctx->streams[videoStream]->codec) != 0) { fprintf(stderr, "Couldn't copy codec context"); return -1; // Error copying codec context } // Open codec if(avcodec_open2(pCodecCtx, pCodec, NULL)<0) return -1; // Could not open codec // Allocate video frame pFrame=av_frame_alloc(); // Allocate an AVFrame structure pFrameRGB=av_frame_alloc(); // Determine required buffer size and allocate buffer numBytes=avpicture_get_size(AV_PIX_FMT_RGB24, ifmt_ctx->streams[videoStream]->codec->width, ifmt_ctx->streams[videoStream]->codec->height); buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t)); // Assign appropriate parts of buffer to image planes in pFrameRGB // Note that pFrameRGB is an AVFrame, but AVFrame is a superset // of AVPicture avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_BGR24, ifmt_ctx->streams[videoStream]->codec->width, ifmt_ctx->streams[videoStream]->codec->height); av_dump_format(ofmt_ctx, 0, out_filename, 1); if (!(ofmt->flags & AVFMT_NOFILE)) { ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE); if (ret < 0) { fprintf(stderr, "Could not open output file '%s'", out_filename); goto end; } } ret = avformat_write_header(ofmt_ctx, NULL); if (ret < 0) { fprintf(stderr, "Error occurred when opening output file\n"); goto end; } // Assign appropriate parts of buffer to image planes in pFrameRGB // Note that pFrameRGB is an AVFrame, but AVFrame is a superset // of AVPicture avpicture_fill((AVPicture *)pFrameRGB, buffer, AV_PIX_FMT_BGR24, ifmt_ctx->streams[videoStream]->codec->width, ifmt_ctx->streams[videoStream]->codec->height); // initialize SWS context for software scaling sws_ctx = sws_getContext( ifmt_ctx->streams[videoStream]->codec->width, ifmt_ctx->streams[videoStream]->codec->height, ifmt_ctx->streams[videoStream]->codec->pix_fmt, ifmt_ctx->streams[videoStream]->codec->width, ifmt_ctx->streams[videoStream]->codec->height, AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL ); // Loop through packets while (1) { AVStream *in_stream, *out_stream; ret = av_read_frame(ifmt_ctx, &pkt); if(pkt.stream_index==videoStream) // Decode video frame avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &pkt); if(frameFinished) { sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize); cv::Mat img= mal_frame->process( pFrameRGB,pFrame->width,pFrame->height); /* My problem is Here ------------*/ avpicture_fill((AVPicture*)pFrameRGB, img.data, PIX_FMT_BGR24, outStream->codec->width, outStream->codec->height); pFrameRGB->width = ifmt_ctx->streams[videoStream]->codec->width; pFrameRGB->height = ifmt_ctx->streams[videoStream]->codec->height; avcodec_encode_video2(ifmt_ctx->streams[videoStream]->codec , &pkt , pFrameRGB , &gotPacket); /* I get this error [swscaler @ 0x14b58a0] bad src image pointers [swscaler @ 0x14b58a0] bad src image pointers */ /* My Problem Ends here ---------- */ } if (ret < 0) break; in_stream = ifmt_ctx->streams[pkt.stream_index]; out_stream = ofmt_ctx->streams[pkt.stream_index]; //log_packet(ifmt_ctx, &pkt, "in"); /* copy packet */ pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF); pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF); pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base); pkt.pos = -1; log_packet(ofmt_ctx, &pkt, "out"); ret = av_interleaved_write_frame(ofmt_ctx, &pkt); if (ret < 0) { fprintf(stderr, "Error muxing packet\n"); break; } av_free_packet(&pkt); } av_write_trailer(ofmt_ctx); end: avformat_close_input(&ifmt_ctx); /* close output */ if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE)) avio_closep(&ofmt_ctx->pb); avformat_free_context(ofmt_ctx); if (ret < 0 && ret != AVERROR_EOF) { return 1; } return 0; } 

When I run this code, I get an unknown fatal error in this part:

  /* My problem is Here ------------*/ avpicture_fill((AVPicture*)pFrameRGB, img.data, PIX_FMT_BGR24, outStream->codec->width, outStream->codec->height); pFrameRGB->width = ifmt_ctx->streams[videoStream]->codec->width; pFrameRGB->height = ifmt_ctx->streams[videoStream]->codec->height; avcodec_encode_video2(ifmt_ctx->streams[videoStream]->codec , &pkt , pFrameRGB , &gotPacket); /* I get this error [swscaler @ 0x14b58a0] bad src image pointers [swscaler @ 0x14b58a0] bad src image pointers */ /* My Problem Ends here ---------- */ 

Here I want to convert cv Mat to AVFrame and encode it to AVPacket. I appreciate your help.

Answer 1

After reading some examples, reading the source code, and some helping people, I managed to run the code. I used transcoding and coding examples and mixed them up. Here is my code

Here are the main points: 1- libswscale should be used to convert an AVFrame with the required package format for submission to openCV Mat. For this we define

 struct SwsContext *sws_ctx = NULL; sws_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL ); 

To convert opencv Mat back to AVFrame, you need to use swscale again and convert the opencv BGR frame format to YUV. So, I am doing this:

  struct SwsContext *sws_ctx_bgr_yuv = NULL; sws_ctx_bgr_yuv = sws_getContext(pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt //AV_PIX_FMT_YUV420p ,0,0,NULL,NULL); 

And here is the read / decode / coding frame cycle:

 while (1) { if ((ret = av_read_frame(ifmt_ctx, &packet)) < 0) break; stream_index = packet.stream_index; type = ifmt_ctx->streams[packet.stream_index]->codec->codec_type; av_log(NULL, AV_LOG_DEBUG, "Demuxer gave frame of stream_index %u\n", stream_index); if (filter_ctx[stream_index].filter_graph) { av_log(NULL, AV_LOG_DEBUG, "Going to reencode&filter the frame\n"); frame = av_frame_alloc(); if (!frame) { ret = AVERROR(ENOMEM); break; } av_packet_rescale_ts(&packet, ifmt_ctx->streams[stream_index]->time_base, ifmt_ctx->streams[stream_index]->codec->time_base); dec_func = (type == AVMEDIA_TYPE_VIDEO) ? avcodec_decode_video2 : avcodec_decode_audio4; ret = dec_func(ifmt_ctx->streams[stream_index]->codec, frame, &got_frame, &packet); if (ret < 0) { av_frame_free(&frame); av_log(NULL, AV_LOG_ERROR, "Decoding failed\n"); break; } if (got_frame) { if(stream_index==video_index){ sws_scale(sws_ctx, (uint8_t const * const *)frame->data, frame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize); /*------------------------------------------------------------------------ /* Frame converts to opencv Mat /*------------------------------------------------------------------------*/ cv::Mat img(frame->height,frame->width,CV_8UC3,pFrameRGB->data[0]); img=manipulate_image(img); //this is opencv Mat, do whatever you want, but don't change its dimensions and format //manipulate_function can be considered as as simple as blurring const int stride[] = {img.step[0] }; /* opencv Mat converts back to AVFrame */ sws_scale(sws_ctx_bgr_yuv, &img.data, stride, 0, img.rows, frame->data, frame->linesize); } frame->pts = av_frame_get_best_effort_timestamp(frame); /* AVFrame re-encodes to AVPacket and will be sent to encoder */ ret = filter_encode_write_frame(frame, stream_index); av_frame_free(&frame); if (ret < 0) goto end; } else { av_frame_free(&frame); } } else { /* remux this frame without reencoding */ av_packet_rescale_ts(&packet, ifmt_ctx->streams[stream_index]->time_base, ofmt_ctx->streams[stream_index]->time_base); ret = av_interleaved_write_frame(ofmt_ctx, &packet); if (ret < 0) goto end; } av_free_packet(&packet); } 

Answer 2

Here is another way to convert between cv::Mat and AVframe using C ++ based on some code that I found and debugged. Please note that this is specifically for 8-bit 3-channel images, but this can be changed by changing AV_PIX_FMT_BGR24 in both functions.

Hope this helps.

 AVFrame cvmat_to_avframe(cv::Mat* frame) { AVFrame dst; cv::Size frameSize = frame->size(); AVCodec *encoder = avcodec_find_encoder(AV_CODEC_ID_RAWVIDEO); AVFormatContext* outContainer = avformat_alloc_context(); AVStream *outStream = avformat_new_stream(outContainer, encoder); avcodec_get_context_defaults3(outStream->codec, encoder); outStream->codec->pix_fmt = AV_PIX_FMT_BGR24; outStream->codec->width = frame->cols; outStream->codec->height = frame->rows; avpicture_fill((AVPicture*)&dst, frame->data, AV_PIX_FMT_BGR24, outStream->codec->width, outStream->codec->height); dst.width = frameSize.width; dst.height = frameSize.height; return dst; } cv::Mat avframe_to_cvmat(AVFrame *frame) { AVFrame dst; cv::Mat m; memset(&dst, 0, sizeof(dst)); int w = frame->width, h = frame->height; m = cv::Mat(h, w, CV_8UC3); dst.data[0] = (uint8_t *)m.data; avpicture_fill( (AVPicture *)&dst, dst.data[0], AV_PIX_FMT_BGR24, w, h); struct SwsContext *convert_ctx=NULL; enum AVPixelFormat src_pixfmt = AV_PIX_FMT_BGR24; enum AVPixelFormat dst_pixfmt = AV_PIX_FMT_BGR24; convert_ctx = sws_getContext(w, h, src_pixfmt, w, h, dst_pixfmt, SWS_FAST_BILINEAR, NULL, NULL, NULL); sws_scale(convert_ctx, frame->data, frame->linesize, 0, h, dst.data, dst.linesize); sws_freeContext(convert_ctx); return m; }