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• 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

• 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

• How to convert VP8 track with different frame resolution to h264

  13 septembre 2016, par Nikita

  I have a .webm file with VP8 track, recorded from WebRTC stream by external service (TokBox Archiving). The stream is adaptive, so each frame in track could have different resolution. Most players (in webkit browsers) use video resolution from track description (which is always 640x480) and scale frames to this resolution. Firefox and VLC player uses real frame resolution, changing video resolution respectively.

  I want to achieve 2 goals :

  1. play this video in Internet Explorer 9+ without additional plugin installation.
  2. change frames resolution to one fixed resolution, so the video will look identically in different browsers.

  So, my plan is :

  • extract frames from source webm file to images with real frame resolution (e.g. PNG or BMP) (how could I do that ?)
  • find max width and max height of images
  • add black padding to images, so smaller frames will be in the center of a new frame (of size MAX_WIDHTxMAX_HEIGHT)
  • combine images to h264 track using ffmpeg

  Is all correct ? How can I achieve this ? Can this algorithm be optimized some way ?

  I tried ffmpeg to extract images, but it does not parse real frame resolution, using resolution from track header.
  I think some libwebm functions can help me (to parse frame headers and extract images). Maybe someone has some code snippets to do this ?

  Example .webm (download source, do not play google-converted version) : https://drive.google.com/file/d/0BwFZRvYNn9CKcndhMzlVa0psX00/view?usp=sharing

  Official description of adaptive stream from TokBox support : https://support.tokbox.com/hc/en-us/community/posts/206241666-Archived-video-resolution-is-supposed-to-be-720x1280-but-reports-as-640x480