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• Dealing with problems in FLAC audio files with ffmpeg

  15 janvier 2020, par Seamus

  I have gotten a set of FLAC (audio) files from a friend. I copied them to my Sonos music library, and got set to enjoy a nice album. Unfortunately, Sonos would not play the files. As a result I have been getting to know ffmpeg.

  Sonos’ complaint with the FLAC files was that it was "encoded at an unsupported sample rate". With rolling eyes and shaking head, I note that the free VLC media player happily plays these files, but the product I’ve paid for (Sonos) - does not. But I digress...

  ffprobe revealed that the FLAC files contain both an Audio channel and a Video channel :

  $ ffprobe -hide_banner  -show_streams "/path/to/Myaudio.flac"
  
  
  
  
  
      Duration: 00:02:23.17, start: 0.000000, bitrate: 6176 kb/s  
  
      Stream #0:0: Audio: flac, 176400 Hz, stereo, s32 (24 bit)  
  
      Stream #0:1: Video: mjpeg (Progressive), yuvj444p(pc, bt470bg/unknown/unknown), 450x446 [SAR 72:72 DAR 225:223], 90k tbr, 90k tbn, 90k tbc (attached pic)  
  
      Metadata:  
  
        comment         : Cover (front)  

  Cool ! I guess this is how some audio players are able to display the ’album artwork’ when they play a song ? Note also that the Audio stream is reported at 176400 Hz ! Apparently I’m out of touch ; I thought that 44.1khz sampling rate effectively removed all of the ’sampling artifacts’ we could hear. Anyway, I learned that Sonos would support a max of 48kHz sampling rate, and this (the 176.4kHz rate) is what Sonos was unhappy about. I used ffmpeg to ’dumb it down’ for them :

  $ ffmpeg -i "/path/to/Myaudio.flac" -sample_fmt s32 -ar 48000 "/path/to/Myaudio48K.flac"

  This seemed to work - at least I got a FLAC file that Sonos would play. However, I also got what looks like a warning of some sort :

  [swscaler @ 0x108e0d000] deprecated pixel format used, make sure you did set range correctly
  [flac @ 0x7feefd812a00] Frame rate very high for a muxer not efficiently supporting it.
  Please consider specifying a lower framerate, a different muxer or -vsync 2

  A bit more research turned up this answer which I don’t quite understand, and then in a comment says, "not to worry" - at least wrt the swscaler part of the warning.

  And that (finally) brings me to my questions :

  1.a. What framerate, muxer & other specifications make a graphic compatible with a majority of programs that use the graphic ?

  1.b. How should I use ffmpeg to modify the Video channel to set these specifications (ref. Q 1.a.) ?

  2.a. How do I remove the Video channel from the .flac audio file ?

  2.b. How do I add a Video channel into a .flac file ?

  EDIT :

  I asked the above (4) questions after failing to accomplish a ’direct’ conversion (a single ffmpeg command) from FLAC at 176.4 kHz to ALAC (.m4a) at 48 kHz (max supported by Sonos). I reasoned that an ’incremental’ approach through a series of conversions might get me there. With the advantage of hindsight, I now see I should have posted my original failed direct conversion incantation... we live and learn.

  That said, the accepted answer below meets my final objective to convert a FLAC file encoded at 176.4kHz to an ALAC (.m4a) at 48kHz, and preserve the cover art/video channel.

• Which Platform/Language to choose for Video Management System [closed]

  5 décembre 2019, par Vivek Buddhadev

  We have started on a new project, Which enables for the multiple IP cameras(Around 1000 Cameras) to record as well as available for live streaming.

  Like https://www.security.honeywell.com/uk/product-repository/maxpro-vms

  Initially, we have tried using ffmpeg commands that saves data in chunks :

  ffmpeg -i {rtsp_url} -fflags flush_packets -max_delay 2 -flags -global_header \
  
      -hls_time 2 -hls_list_size 3 -vcodec copy -y /var/www/html/Cam01.m3u8

  Then we have started http server and using node.js we are displaying the stream.

  But as we are adding more cameras into it, the performance is going down.

  Kindly suggest if there is any other way to achieve this functionality which help us to fulfill the above requirement.

• Bulk identifying images with FFMPEG that contain a graphic

  26 septembre 2019, par edwardv

  I need to be able to bulk sort through images that contain a graphic and remove these images from the folder. The graphic is a ruler-like image for scale.

  I’m a novice with FFMPEG, but have already written a batch script that resizes images. The logic seems pretty understandable, however my issue is that I don’t know what and where to research for a solution to my problem. From what I read, imagemagik might also be a great tool, but I feel more comfortable with FFMPEG.

  I expect the script to look through all image files in a folder and find those the contain the ruler graphic and remove the said images with the rule graphic from the folder. The images are product shots on white backgrounds and the rule graphic is not overlaying anything or acting like a watermark.

  Ideally, if possible, a way to crop out the graphics would be an amazing next step.