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• Avoiding ffmpeg audio drift for live dash output

  22 mai 2021, par mdale

  Have people experienced playback drift with ffmpeg based dash segment generation ? For example :

  


  ffmpeg -threads 2 -re -fflags +genpts -stream_loop -1 -i AVSyncTest.mp4 \
-af "aresample=async=1:min_hard_comp=0.100000:first_pts=0" \
-c:v:0 libx264 \
-pix_fmt:0 yuv420p \
-preset:0 medium \
-a53cc:0 1 \
-nal-hrd:0 cbr \
-x264opts:0 scenecut=-1:rc_lookahead=0 -b:v:0 5000k -bufsize:0 500k \
-force_key_frames:0 "expr:gte(t,n_forced*2)" \
-bf:0 8 \
-r 30 \
-c:a:0 aac  -ar 48000 \
-b:a:1 96k  \
-f tee -map 0:v \
-map 0:a "[f=dash:media_seg_name='chunk-stream_\$RepresentationID\$-\$Number%05d\$.mp4':init_seg_name='init-stream_\$RepresentationID\$.mp4':seg_duration=2:utc_timing_url=https\\\://time.akamai.com\\?iso:remove_at_exit=0:use_timeline=0:http_user_agent=ffmpeg_encoder.0:streaming=1:index_correction=1:timeout=1:dash_segment_type=mp4:method=PUT:http_persistent=1:adaptation_sets='id=0,streams=v\:0 id=1,streams=a' ]http://localhost:5000/out.mpd "


  


  After a bit of playback it starts audio starts to drift. Analysis of the moof (with tools like mp4box) shows 1024 sample size with 93 Moofs with Moof->traf->default_sample_duration=1024 at 48000 sample rate giving segment duration of 1.984 seconds with every 3rd segment or so with 92 Moofs with duration of 1.962 … While each segment starts aligned ( if you reset playback you get alignment) it drifts against continuous playback.

  


  Other examples like Akamai’s public stream. show 94 Moofs or 2.005 duration with every 3rd segment or so at the 1.984 duration. (what one would want)

  


  Akamai’s (presumably ffmepg based) stream is averaging out to the 2s target where the above ffmpeg command is not …

  


• avcodec/hashtable : Only free buffer if there is buffer to free

  3 juin, par Andreas Rheinhardt

  avcodec/hashtable : Only free buffer if there is buffer to free
  Reviewed-by : Emma Worley <emma@emma.gg>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/hashtable.c

• Could you please guide me on how to play a single sample of an audio file in C# using FFmpeg ?

  11 juillet 2023, par hello world

  What is the recommended approach for playing a single sample of an audio file in C# using FFmpeg ? I would like to incorporate FFmpeg into my C# application to play a specific sample from an audio file. Could someone provide an example or guide me on how to achieve this ? Any help would be appreciated.

  


  using System;
using System.Diagnostics;

public class AudioPlayer
{
    private string ffmpegPath;

    public AudioPlayer(string ffmpegPath)
    {
        this.ffmpegPath = ffmpegPath;
    }

    public void PlayAudioSample(string audioFilePath, TimeSpan samplePosition)
    {
        // Prepare FFmpeg process
        Process ffmpegProcess = new Process();
        ffmpegProcess.StartInfo.FileName = ffmpegPath;
        ffmpegProcess.StartInfo.Arguments = $"-ss {samplePosition} -i \"{audioFilePath}\" -t 1 -acodec pcm_s16le -f wav -";
        ffmpegProcess.StartInfo.RedirectStandardOutput = true;
        ffmpegProcess.StartInfo.RedirectStandardError = true;
        ffmpegProcess.StartInfo.UseShellExecute = false;
        ffmpegProcess.StartInfo.CreateNoWindow = true;

        // Start FFmpeg process
        ffmpegProcess.Start();

        // Play audio sample
        using (var audioOutput = new NAudio.Wave.WaveOutEvent())
        {
            using (var audioStream = new NAudio.Wave.RawSourceWaveStream(ffmpegProcess.StandardOutput.BaseStream, new NAudio.Wave.WaveFormat(44100, 16, 2)))
            {
                audioOutput.Init(audioStream);
                audioOutput.Play();
                while (audioOutput.PlaybackState == NAudio.Wave.PlaybackState.Playing)
                {
                    System.Threading.Thread.Sleep(100);
                }
            }
        }

        // Wait for FFmpeg process to exit
        ffmpegProcess.WaitForExit();
    }
}