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• ffmpeg incorrectly adds a fixed delay to the end of each video chunk

  13 janvier 2023, par Skyler

  I am trying to combine audio a video data to output as an mp4 file using the command below, the videos are segmented to match the exact length of the audio file they are going to be merged with :

  


      command = 'ffmpeg -y -i {} -i {} -strict -2 -q:v 1 {} -loglevel {} -c:v h264_nvenc'.format(
        audio_file, temp_result_avi, outfile, self.ffmpeg_loglevel
    )
    subprocess.call(command, shell=True)


  


  however each video made by this is exactly 24 ms longer so this causes large delays as they get stitched back together. This doesnt work since the combined video needs to be combined back with another video and the desync gets worse as you get further in the combined videos.

  


  How can I remedy this ?

  


• Capturing actual video stream quality using FFmpeg and FFplay – smooth recording but stuttering stream

  3 décembre 2024, par Karlitos Bemowo

  I’m trying to analyze the quality of a video stream over a local network using FFmpeg. My goal is to capture the actual streamed video (with all artifacts, stuttering, or buffering) as experienced in real-time, rather than a reconstructed, smooth output. Currently, the recorded video is perfectly smooth, but the live stream played using ffplay exhibits noticeable stuttering. Additionally, while the duration of the recording matches the original video, the live stream lasts longer, likely due to buffering caused by network instability.

  


  Here are the commands I’m using :
Sender :
ffmpeg -re -i file.mp4 -c:v libx265 -preset veryfast -f mpegts udp ://192.168.1.26:1234
Receiver :
ffmpeg -i udp ://192.168.1.10:1234 -c copy received_fhd.mp4 -fflags nobuffer

  


  The recorded file received_fhd.mp4 plays back perfectly, with no stuttering or frame drops, even though the network stream has visible issues when viewed in real-time with ffplay.The recorded file has the same duration as the original video (fhd.mp4), while the real-time stream playback with ffplay takes longer, suggesting delays caused by buffering or network issues. Same issue with with other codes for example vp9.

  


  GOAL : I want to capture the actual streamed video as experienced in real-time, with all stuttering, buffering, and artifacts included. This would allow me to analyze the network's impact on the video quality effectively.

  


  Questions :

  


  

  1. How can I modify my commands to record the video stream exactly as it is experienced in real-time, including any network-induced issues ?

  


  2. Is there a way to configure FFmpeg to behave more like ffplay in terms of handling and recording the stream ?

  


  


  Any guidance or alternative approaches would be greatly appreciated. Thank you !

  


  Experimented with different codecs (e.g., H.265, VP9) and output formats. Older codes has no delay in tranmission so I didn't notice the issue at frist.

  


  Explored various ffmpeg options like -fflags nobuffer and -c copy (as documentation says " For example, -codec copy or -codec : copy would copy all the streams without reencoding."), but it still doesn’t replicate the actual stream behavior.

  


• Automatically choose appropriate libvpx codec ffmpeg

  26 août 2022, par Jakob Košir

  When extracting alpha channel from a vp8 or vp9 video libvpx input decoder has to be specified, as native ffmpeg one doesn't support reading alpha data from vp8/vp9.

  


  So either ffmpeg -c:v libvpx -i  ... for VP8 and ffmpeg -c:v libvpx-vp9 -i  ... for VP9.

  


  Is there a way to tell ffmpeg to use the appropriate libvpx decoder based on input file (vp8 vs vp9) instead of native ffmpeg input decoder ? So that separate commands for vp8 and vp9 would no longer be needed.