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• Bitrate variation in x264 encode ? [closed]

  21 octobre 2012, par nightcrawler

  Under win732bit
  The following picture is the analysis of bitrateviewer from 2 different encodings :
  
  After learning a great deal I want to ask some basic questions

  • Are the jitters (huge variation of bitrate) in the encoded files
    (relative to original .wmv) usual or they refer to poor results ? (I
    used CBR this should have given me a nice smooth bitrate histogram ?)
  • Am I correct in setting level to 3.1 because this is enough to handle
    the input resolution & bitrate ?
    (http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Levels)
  • Would you recommend me for CBR(currently used at 23) or
    2pass(2500kb/s) or ABR(2500kb/s) for this file ? (I assume that the
    latter of the two will reduce jitters but increase filesize because
    bitrate is kept constant even in those frames where its not needed or
    willlnt produce influential results)
  • Provided that I want good result under 260mb what are the setting I
    have to use ?

• Stream map '0:a:0' matches no streams

  6 décembre 2019, par Сергей Барахтенко

  To encode a video using FFMPEG the following command is used :

  /usr/bin/ffmpeg -i INPUT.MP4 
  
  -preset veryfast -r 25 -g 75 -threads 4 -sc_threshold 0 
  
  -map 0:v:0 -map 0:a:0 
  
  -filter:v:0 scale=h=240:w=-2  
  
  -minrate:v:0 75k  
  
  -maxrate:v:0 218k  
  
  -bufsize:v:0 300k 
  
  -b:v:0 150k  -c:a aac -b:a 128k -ac 2 
  
  -var_stream_map "v:0,a:0" 
  
  -master_pl_name master.m3u8 
  
  -f hls -hls_time 3 -segment_time 6 
  
  -hls_list_size 0 -segment_format mpegts 
  
  -hls_segment_filename /res-%v/segment-%d.ts  OUTPUT.M3U8  1> log.txt 2>&1 

  In general, despite such a huge command, it copes with the task with a bang

  But there is one little BUT :

  If you run this command on a video WITHOUT audio, there will be an error :

  Stream map '0:a:0' matches no streams. To ignore this, add a trailing '?' to the map.

  Yes, I understand that the command tells me that the audio stream was not found. And to ignore this, you need to add a trailing question mark to the map

  But only I can’t understand where ? to which place ?

  I will be glad to any advice or suggestion

  Thanks in advance

• ffmpeg crops video, but doubles size

  17 février 2017, par Michael Cole

  I rendered an mp4 from kdenlive and it looks great (1920x1080).

  I want to crop the video, and transcode to ogv for browsers.

  I tried this, but the ffmpeg makes a much larger file for the cropped version :

  ffmpeg -i untitled.mp4 -filter:v "crop=1920:760:0:0" masthead.mp4
  
  ffmpeg -i masthead.mp4 masthead.ogv

  This video is background for a web page, so I’m exporting from kdenlive with low quality video settings and no audio.

  Original is untitled.mp4 :

  186907 Feb 16 19:17 untitled.mp4
  
  606241 Feb 16 19:18 masthead.mp4
  
  434127 Feb 16 19:18 masthead.ogv

  The output is here : http://pastebin.com/WYjHAuCC

  untitled.mp4 looks ok (great for it’s purpose). masthead.mp4 looks good but it’s huge, and masthead.ogv is very pixelated.

  Any suggestions ?