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• ffmpeg : recommended bitrate vs resolution [duplicate]

  15 octobre 2016, par Santhosh Yedidi

  This question already has an answer here :

  • FFMPEG sensible defaults
    
    2 answers
    

  I have high resolution video

    Duration: 00:06:28.80, start: 0.000000, bitrate: 15968 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 15809 kb/s, 25 fps, 25 tbr, 25k tbn, 50 tbc (default)
  
      Metadata:
  
        creation_time   : 2016-10-11 05:35:02
  
        handler_name    : Alias Data Handler
  
        encoder         : AVC Coding
  
      Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 157 kb/s (default)
  
      Metadata:
  
        creation_time   : 2016-10-11 05:35:02
  
        handler_name    : Alias Data Handler

  Its 6+min video.

  I am ok with resolution of 240p (because i want to send it on whatsapp)

  In order my video to look good quality what is the recommended bitrate for 240p. Also is what is the minimum bitrate below which the chances of pixelating will be there in the video.

  I dont want to go for high bitrate also. Because ultimately i want the size to be not more than 240p.

  I use mpv to see the video. I scale the original video to 240p, the quality after conversion should match the quality visible in mpv. That will give me first hand idea of how good is the conversion.

  I expect a good amount of reduction in size(MB : where original is 740mb) of the file when reduced from 1920x1080 to 240p

  I have found some information regarding this.

  

  How much is this true

• Different video players showing incorrect mp4 resolution after ffmpeg conversion

  18 novembre 2016, par Nova

  After getting help from http://stackoverflow.com/a/40601020/6318164 on how to convert webm to mp4. The result avoiding losing the video ratio by setting the height resolution with -vf scale=-2:720.

  I then came across another problem. I’ve found both width and height had to be supported for the video players, when I thought it was just the height that had to be specified.

  After browsing around I found this script http://stackoverflow.com/a/35487394/6318164 were I can change the video’s canvas to a common width and height standard. It shrinks the video to fit inside the center of specified canvas without losing the ratio while filling the empty space with black padding if I’m correct, which is the result I want.

  However, although it solved the playback problems in all the players, I’ve found different video players show different resolution information of the same video.

  I’ve modified the script here for Linux terminal use.

  X=1280; Y=720; ffmpeg -i old.webm -t 5 -vf "scale=min(iw*$Y/ih\,$X):min($Y\,ih*$X/iw),pad=$X:$Y:($X-iw)/2:($Y-ih)/2" new.mp4

  This is the research on the resolution differences I’ve found for value I set.

  X=1280; Y=720;
  
  
  
  webm          -> mp4
  
  =========================================================
  
  1280x752      -> 1280x720 X-plore (Android)
  
  Not supported -> 1339x720 Telegram (Android)
  
  1338x752      -> 1340x720 GNOME MPlayer (Linux)
  
  Not supported -> ???????? Built-in Video Player (Android)

  The question is, I’m I doing anything wrong with the ffmpeg conversion to return incorrect resolutions for different players ? I checked out some other videos I have and they show the correct resolutions except this converted one.

  Edit

  With the help of the accepted answer. This was my working output if anyone needs it :

  X=1280; Y=720; ffmpeg -i input.webm -vf "scale='if(gt(a*sar,16/9),${X},${Y}*iw*sar/ih)':'if(gt(a*sar,16/9),${X}*ih/iw/sar,${Y})',pad=${X}:${Y}:(ow-iw)/2:(oh-ih)/2,setsar=1" output.mp4

• avcodec/cuvid : fail early if GPU can’t handle video resolution

  23 janvier 2017, par Pavel Koshevoy

  avcodec/cuvid : fail early if GPU can’t handle video resolution
  CUVID on GeForce GT 730 and GeForce GTX 1060 does not report any error when
  
  decoding 8K h264 packets. However, it does return an error during
  
  cuvidCreateDecoder call if the indicated video resolution is not
  
  supported.
  Given that stream resolution is typically known as a result of probing
  
  it is better to use this information during avcodec_open2 call to fail
  
  immediately, rather than proceeding to decode and never receiving any
  
  frames from the decoder nor receiving any indication of decode failure.
  Signed-off-by : Timo Rothenpieler <timo@rothenpieler.org>
  

  • [DH] libavcodec/cuvid.c