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• Encoding parameters in videos for web (low in size) while keeping quality good enough ?

  10 juillet 2012, par umutto

  I'm trying to build a video sharing platform much like youtube. So far everything is going great, but i'm having difficulties with my encoding parameters in ffmpeg. I'm using a silverlight media player so the output file must be in wmv format.

  The only thing i can play freely was -qscale parameter and it gets shabby after 8. And i downloaded some youtube videos and they seem to keep amazing quality (definitely not -qscale 8 can achieve) with very low file sizes.

  So what i'm asking is some patterns that can help me convert a video to high, mid and low quality wmv videos.

  The codec i use right now is pretty simple and useless is like this ; (oh btw audio must keep 128k or higher quality for mid and high)

     ffmpeg -i a1.wmv -vcodec wmv2 -qscale 2 -s 852x480 -acodec wmav2 -ar 44100 -ab 128k -y a480.wmv
  
     ffmpeg -i a1.wmv -vcodec wmv2 -qscale 4 -s 640x360 -acodec wmav2 -ar 44100 -ab 128k -y a360.wmv
  
     ffmpeg -i a1.wmv -vcodec wmv2 -qscale 6 -s 354x200 -acodec wmav2 -ar 44100 -ab 128k -y a200.wmv

  the output quality i achieve with this command is more than enough but the sizes are usually 10 times larger than a youtube video near the same or less quality.

  Thanks in advance !

• Maintaining exact aspect ratio when scaling videos using ffmpeg

  31 mai 2012, par Skkard

  I have a mkv video, which is a mix of multiple resolution recordings, e.g. I have the first few seconds of widescreen 16:9 (1024x576) resolution, and the rest of the video if 4:3 (768x576) resolution. I want to scale this video down 3 times, while copying all the other attributes (audio codec, subtitles etc.). I use ffmpeg -i  -vf scale=iw/2:-1 -acodec copy . Also, VLC detects it's resolution as 720x576.

  The problem is that after the scaling, the resolution constantly becomes 4:3 (360x288). How can I maintain the dynamic aspect ratio of the input video file i.e. the 16:9 parts to scale to 16:9, while the 4:3 parts scale to 4:3 ?

  update

  The player size actually changes, atleast in mplayer, when the resolution is switched. I figured out the main problem. It seems each frame is tagged with a Sample Aspect Ratio (SAR), so when the player plays it, it can find the display aspect ratio. This SAR value isn't getting copied over when encoding to MKV. When encoding to MPG, it does get copied over and I get an exact copy, with the player switching sizes, but not with MKV.

  Output of ffprobe -show_streams filename :

  ffprobe version 0.10.3 Copyright (c) 2007-2012 the FFmpeg developers
  
    built on May  9 2012 17:51:07 with gcc 4.7.0 20120505 (prerelease)
  
    configuration: --prefix=/usr --enable-libmp3lame --enable-libvorbis --enable-libxvid --enable-libx264 --enable-libvpx --enable-libtheora --enable-libgsm --enable-libspeex --enable-postproc --enable-shared --enable-x11grab --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libschroedinger --enable-libopenjpeg --enable-librtmp --enable-libpulse --enable-gpl --enable-version3 --enable-runtime-cpudetect --disable-debug --disable-static
  
    libavutil      51. 35.100 / 51. 35.100
  
    libavcodec     53. 61.100 / 53. 61.100
  
    libavformat    53. 32.100 / 53. 32.100
  
    libavdevice    53.  4.100 / 53.  4.100
  
    libavfilter     2. 61.100 /  2. 61.100
  
    libswscale      2.  1.100 /  2.  1.100
  
    libswresample   0.  6.100 /  0.  6.100
  
    libpostproc    52.  0.100 / 52.  0.100
  
  Input #0, matroska,webm, from 'sample.mkv':
  
    Metadata:
  
      title           : Pan prstenu. Dve veze
  
    Duration: 00:00:29.80, start: 0.000000, bitrate: 3124 kb/s
  
      Stream #0:0(eng): Video: mpeg2video (Main), yuv420p, 720x576 [SAR 64:45 DAR 16:9], 15000 kb/s, 25 fps, 25 tbr, 1k tbn, 50 tbc (default)
  
      Stream #0:1(cze): Audio: mp2, 48000 Hz, stereo, s16, 128 kb/s (default)
  
  [STREAM]
  
  index=0
  
  codec_name=mpeg2video
  
  codec_long_name=MPEG-2 video
  
  codec_type=video
  
  codec_time_base=1/50
  
  codec_tag_string=[0][0][0][0]
  
  codec_tag=0x0000
  
  width=720
  
  height=576
  
  has_b_frames=1
  
  sample_aspect_ratio=64:45
  
  display_aspect_ratio=16:9
  
  pix_fmt=yuv420p
  
  level=8
  
  timecode=16:35:19:10
  
  id=N/A
  
  r_frame_rate=25/1
  
  avg_frame_rate=25/1
  
  time_base=1/1000
  
  start_time=0.000000
  
  duration=N/A
  
  nb_frames=N/A
  
  TAG:language=eng
  
  [/STREAM]
  
  [STREAM]
  
  index=1
  
  codec_name=mp2
  
  codec_long_name=MP2 (MPEG audio layer 2)
  
  codec_type=audio
  
  codec_time_base=1/48000
  
  codec_tag_string=[0][0][0][0]
  
  codec_tag=0x0000
  
  sample_fmt=s16
  
  sample_rate=48000
  
  channels=2
  
  bits_per_sample=0
  
  id=N/A
  
  r_frame_rate=0/0
  
  avg_frame_rate=125/3
  
  time_base=1/1000
  
  start_time=0.000000
  
  duration=N/A
  
  nb_frames=N/A
  
  TAG:language=cze
  
  [/STREAM]

• Mass Watermark Videos with Different Formats/Dimensions Programmatically

  17 septembre 2012, par ColorWP.com

  Is there a way to programmatically (using PHP) convert a directory full of videos with all kinds of formats (avi, mp4, mpeg, wmv) with different dimensions to a single format output (e.g. mp4) with the same dimensions as the input video and with a custom image watermark at the same position over the video (e.g. bottom left). Preferably, without lowering video quality and without making the watermark too large or too small for the resolution (maybe relative size to the video dimensions ?).