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• ffmpeg quality issues

  4 mai 2012, par Chris Vincze

  I'm trying to encode MPEG2 files for broadcast. The spec is MPEG-2 @ 50Mbps with all frames as intra frames.

  So I've done a few experiments and have come across a conundrum.

  Setting the q flags like this :

  ffmpeg -i input.%04d.dpx -vcodec mpeg2video -pix_fmt yuv422p -intra -qmin 1 -qscale 1 -output.mpg

  gives a constant q=1.0 while transcoding and produces a file of approximately 25Mbps (although weirdly the file bitrate is given as : bitrate : 25551 kb/s while the actual stream is specified as 104857 kb/s)

  Duration : 00:01:29.95, start : 1.000000, bitrate : 25551 kb/s
  Stream #0.0[0x1e0] : Video : mpeg2video, yuv422p, 720x608 [PAR 608:405 DAR 16:9], 104857 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
  Stream #0.1[0x1c0] : Audio : mp2, 48000 Hz, 2 channels, s16, 384 kb/s

  However, specifying a constant bit rate like this :

  ffmpeg -i input.%04d.dpx -vcodec mpeg2video -pix_fmt yuv422p -intra -b 50000k -minrate 50000k -maxrate 50000k -bufsize 2000000 -output.mpg

  gives a varying q whilst transcoding somewhere between 1 and 6. The resulting file is 50Mbps (in both the file and the video stream)

  However the quality of this file is not as good as the 25Mbps (as suggested by the q factor).

  So my question is how can I produce a file of 50Mbps AND q=1. It is my understanding that the q flags and the bitrate flags are mutually exclusive (I've tried running both).

  Thanks very much for your help.

• Transition effects between images using ImageMagick and FFMPEG [closed]

  7 mai 2013, par user1599914

  I'm trying to generate a video using still images. I'm using Image Magick's convert command to duplicate the images.

  convert screen6.png -duplicate 10 -background black -gravity center -extent 1024x576 4%06d.screen.transition.png

  I then use ffmpeg to encode the images.

  Problem 1 : How can I achieve good transition effects between the images ; effects such as circle in, box out, wheel, as well as kenburns effect.

  Problem 2 : How can I overlay the images with text, and make that text to animate or appear with some effects such as fade in, zoom out.

  Your help will be greatly appreciated.

• ffmpeg network congestion(block)

  13 mai 2013, par user1855127

  everyone !
  I use ffmpeg (avformat_open_input()) to open a network stream example "mms".
  And then ,i read frames 、decoder and play.
  Finall close it with avformat_close_input().

  Above process are no problem.

  Problem :
  I want to cycle the operation above, such as switch mms url. Like switch "mms ://url_one" to "mms ://url_two". The "mms:url_one" operation is good . But "mms ://url_two" is congestion(block) in avformat_read_frame().

  PS :
  I also try av_open()、av_read()、av_close() to get the datas. But get the same result like above.

  Q:has anyone who know this ?Thanks !