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• avcodec/cbs_mpeg2 : Simplify splitting fragment

  4 février 2022, par Andreas Rheinhardt

  avcodec/cbs_mpeg2 : Simplify splitting fragment
  avpriv_find_start_code() supports non-contiguous buffers
  
  by maintaining a state that allows to find start codes
  
  that span across multiple buffers ; a consequence thereof
  
  is that avpriv_find_start_code() is given a zero-sized
  
  buffer, it does not modify this state, so that it appears
  
  as if a start code was found if the state contained a start code.
  This can e.g. happen with Sequence End units in MPEG-2 and
  
  to counter this, cbs_mpeg2_split_fragment() reset the state
  
  when it has already encountered the end of the fragment
  
  in order to add the last unit (if it is only of the form 00 00 01 xy)
  
  only once ; it also used a flag to set whether this is the final unit.
  Yet this can be improved by simply resetting state unconditionally
  
  (thereby avoiding a branch) ; the flag can be removed by just checking
  
  whether we have a valid start code (of the next unit to add)
  
  at the end.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/cbs_mpeg2.c

• Exception thrown at 0x7C2E6005 (swscale-5.dll) in Video_playing.exe : 0xC0000005 : Access violation reading location 0xCCCCCD04 [closed]

  11 mai 2020, par jatin yadav

  Trying to play a video using GLFW and FFmpeg on visual studio 2019 on windows 10.

  



  Exception is thrown at sws_scale(sws_scaler_ctx, av_frame->data, av_frame->linesize, 0, av_frame->height, dest, dest_linesize) ; in the code. Don't know why this is occurred. Please Help !!

  



  #include "video_reader.h"
#include 

bool video_reader_read_frame(VideoReaderState* state, uint8_t* frame_buffer, int64_t* pts) {

    // Unpack members of state
    auto& width = state->width;
    auto& height = state->height;
    auto& av_format_ctx = state->av_format_ctx;
    auto& av_codec_ctx = state->av_codec_ctx;
    auto& video_stream_index = state->video_stream_index;
    auto& av_frame = state->av_frame;
    auto& av_packet = state->av_packet;
    auto& sws_scaler_ctx = state->sws_scaler_ctx;

    // Decode one frame
    int response;
    while (av_read_frame(av_format_ctx, av_packet) >= 0) {
        if (av_packet->stream_index != video_stream_index) {
            av_packet_unref(av_packet);
            continue;
        }

        response = avcodec_send_packet(av_codec_ctx, av_packet);
        if (response < 0) {
            printf("Failed to decode packet: %s\n", response);
            return false;
        }

        response = avcodec_receive_frame(av_codec_ctx, av_frame);
        if (response == AVERROR(EAGAIN) || response == AVERROR_EOF) {
            av_packet_unref(av_packet);
            continue;
        }
        else if (response < 0) {
            printf("Failed to decode packet: %s\n", response);
            return false;
        }

        av_packet_unref(av_packet);
        break;
    }

    *pts = av_frame->pts;

    // Set up sws scaler
    if (!sws_scaler_ctx) {
        sws_scaler_ctx = sws_getContext(width, height, av_codec_ctx->pix_fmt,
            width, height, AV_PIX_FMT_RGB0,
            SWS_BILINEAR, NULL, NULL, NULL);
    }
    if (!sws_scaler_ctx) {
        printf("Couldn't initialize sw scaler\n");
        return false;
    }

    uint8_t* dest[4] = { frame_buffer, NULL, NULL, NULL };
    int dest_linesize[4] = { width * 4, 0, 0, 0 };
    sws_scale(sws_scaler_ctx, av_frame->data, av_frame->linesize, 0, av_frame->height, dest, dest_linesize);

    return true;
}


  


• How to accurately detect the start of the main beat and soundtracks in diverse audio tracks ?

  18 juin 2024, par SnoofFloof

  I'm working on a project where I need to edit soundtracks. The challenge is to detect when the main beat and melody of any given soundtrack is properly developed. I am certain there is better terminology to describe what I am aiming for, but ideally, I want to skip the "build-up" and immediately have the song starting at the "main part". This needs to work for various songs across different genres, which often have different structures and onset patterns, making it difficult to streamline the process.

  


  For example :

  


  https://www.youtube.com/watch?v=P77CNtHrnmI -> I would want to my code to identify the onset at 0:24

  


  https://www.youtube.com/watch?v=OOsPCR8SyRo -> Onset detection at 0:12

  


  https://www.youtube.com/watch?v=XKiZBlelIzc -> Onset detection at 0:19

  


  I've tried using librosa to analyze the onset strength and detect beats, but the current implementation either detects the very beginning of the song or fails to consistently identify when the beat is fully developed.

  


  This was my approach ;

  


  def analyze_and_edit_audio(input_file, output_file):
    y, sr = librosa.load(input_file)
    tempo, beat_frames = librosa.beat.beat_track(y=y, sr=sr)
    beat_times = librosa.frames_to_time(beat_frames, sr=sr)
    main_beat_start = beat_times[0]


  


  I have very little experience with librosa/audio editing, so I would appreciate any suggestions you might have !