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• How to gain volumes of specific bands of audio files using ffmpeg ?

  10 mai 2019, par Ko Ohhashi

  I want increase or decrease volume of specific frequency bands with ffmpeg.

  I think bandreject and bandpass filter can do similar thing.
  But is there any way to reject 80% of energy of specific bands ?

  Thanks in advance ?

• using FFmpeg, how to decode H264 packets

  28 mars 2017, par Jun

  I’m new to FFmpeg struggling to decode H264 packets which can be obtained as an array of uint8_t.

  After many of investigations, I think it should be able to just put the array into an AVPacket like the below

  AVPacket *avpkt = (AVPacket *)malloc(sizeof(AVPacket) * 1);
  
  av_init_packet(avpkt);  
  
  avpkt->data = ct;   // ct is the array
  
  avpkt->length =....

  and decode by avcodec_decode_video2(). A part of the code is like

  ...
  
  codec = avcodec_find_decoder(CODEC_ID_H264);
  
  gVideoCodecCtx = avcodec_alloc_context();
  
  gFrame = avcodec_alloc_frame();
  
  avcodec_decode_video2(gVideoCodecCtx, gFrame, &frameFinished, packet);
  
  ...

  I guess I set all required properties properly but this function is returning only -1 :(

  I just found the -1 is coming from

  ret = avctx->codec->decode(avctx, picture, got_picture_ptr, avpkt) ;

  in the avcodec_decode_video2() ;

  Actually, what I’m wondering is if I can decode H264 packets (without RTP header) by avcodec_decode_video2().

  Thanks for the help in advance.

  ---

  /////////// added

  OK, I’m still trying to find a solution. What I’m doing now is the below

  ** the H264 stream in this RTP stream is encoded by FU-A

  1. receive a RTP packet

  2. look if the second byte of the RTP header is > 0 which means it’s the first packet (and possibly will be followed)

  3. see if the next RTP packet has > 0 at its second byte also, then it means the previous frame was a complete NAL or if this is < 0, the packet should be appended to the previous packet.

  4. remove all RTP header of the packets so it has only like FU indicator | FU header | NAL

  5. try play it with avcodec_decode_video2()

  but it’s only returning -1..... am I supposed to remove FU indicator and header too ??

  any suggestion will be very appreciated

  thanks in advance.

• how to decode h264 data from rtsp stream directively to BGR24 pixel format for cv::Mat or cv::cuda::GpuMat with ffmpeg c lib on NVIDIA GPU ?

  30 septembre 2019, par Wussup

  I want decode h264 dirctively to cv::Mat or cv::cuda::GpuMat without sws_scale to saving CPUs.

  So is there any way to make it realized ? thanks in advance.