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• ffmpeg library - why does the Bitrate parameter change on encoding, and how do I force to preserve it ?

  22 avril 2021, par QRrabbit

  Hello forum and all the members of the community !

  


  I have this question on ffmpeg library, why does the bitrate parameter not retained after encoding, even though I explicitly specify the desired rate.

  


  Input file ffprobe :

  


    Duration: 00:00:10.01, start: 0.000000, bitrate: 534719 kb/s
    Stream #0:0(eng): Video: qtrle (rle  / 0x20656C72), argb(progressive), 1920x1080, 533881 kb/s, SAR 1:1 DAR 16:9, 29.97 fps, 29.97 tbr, 30k tbn, 30k tbc (default)
    Metadata:
      creation_time   : 2021-04-13T16:35:16.000000Z
      handler_name    : Apple Video Media Handler
      encoder         : Animation
      timecode        : 00:00:00;00


  


  Here's the command I run :

  


  ffmpeg -i input.mov -map 0:a? -map 0:s? -pix_fmt argb -b:v 533881667 -maxrate 533881667 -minrate 533881667 -r 29.97 -top 1 -color_range 1 -colorspace 1 -color_primaries 1 -color_trc bt709 -map_metadata 0 -c:a copy -timecode 00:00:00.00 -c:v qtrle -c:s copy output.mov


  


  Output file ffprobe :

  


    Metadata:
    major_brand     : qt  
    minor_version   : 512
    compatible_brands: qt  
    creation_time   : 2021-04-13T16:35:16.000000Z
  Duration: 00:00:10.01, start: 0.000000, bitrate: 100126 kb/s
    Stream #0:0: Video: qtrle (rle  / 0x20656C72), argb(progressive), 1920x1080, 100133 kb/s, SAR 1:1 DAR 16:9, 29.97 fps, 29.97 tbr, 11988 tbn, 11988 tbc (default)
    Metadata:
      creation_time   : 2021-04-13T16:35:16.000000Z
      handler_name    : VideoHandler
      encoder         : Lavf58.58.100
      timecode        : 00:00:00;00


  


  As it is visible from the ffprobe from above, I go from :

  


  The Input's file bitrate : 534719 kb/s
to Output bitrate : 100126 kb/s

  


• PyAV : force new framerate while remuxing stream ?

  7 juin 2019, par ToxicFrog

  I have a Python program that receives a sequence of H264 video frames over the network, which I want to display and, optionally, record. The camera records at 30FPS and sends frames as fast as it can, which isn’t consistently 30FPS due to changing network conditions ; sometimes it falls behind and then catches up, and rarely it drops frames entirely.

  The "display" part is easy ; I don’t need to care about timing or stream metadata, just display the frames as fast as they arrive :

  input = av.open(get_video_stream())
  
  for packet in input.demux(video=0):
  
    for frame in packet.decode():
  
      # A bunch of numpy and pygame code here to convert the frame to RGB
  
      # row-major and blit it to the screen

  The "record" part looks like it should be easy :

  input = av.open(get_video_stream())
  
  output = av.open(filename, 'w')
  
  output.add_stream(template=input.streams[0])
  
  for packet in input.demux(video=0):
  
    for frame in packet.decode():
  
      # ...display code...
  
    packet.stream = output.streams[0]
  
    output.mux_one(packet)
  
  output.close()

  And indeed this produces a valid MP4 file containing all the frames, and if I play it back with mplayer -fps 30 it works fine. But that -fps 30 is absolutely required :

  $ ffprobe output.mp4
  
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 960x720,
  
                    1277664 kb/s, 12800 fps, 12800 tbr, 12800 tbn, 25600 tbc (default)

  Note that 12,800 frames/second. It should look something like this (produced by calling mencoder -fps 30 and piping the frames into it) :

  $ ffprobe mencoder_test.mp4
  
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 960x720,
  
                    2998 kb/s, 30 fps, 30 tbr, 90k tbn, 180k tbc (default)

  Inspecting the packets and frames I get from the input stream, I see :

  stream: time_base=1/1200000
  
  codec: framerate=25 time_base=1/50
  
  packet: dts=None pts=None duration=48000 time_base=1/1200000
  
  frame: dst=None pts=None time=None time_base=1/1200000

  So, the packets and frames don’t have timestamps at all ; they have a time_base which doesn’t match either the timebase that ends up in the final file or the actual framerate of the camera ; the codec has a framrate and timebase that doesn’t match the final file, the camera framerate, or the other video stream metadata !

  The PyAV documentation is all but entirely absent when it comes to issues of timing and framerate, but I have tried manually setting various combinations of stream, packet, and frame time_base, dts, and pts with no success. I can always remux the recorded videos again to get the correct framerate, but I’d rather write video files that are correct in the first place.

  So, how do I get pyAV to remux the video in a way that produces an output that is correctly marked as 30fps ?

• Force a vbscript to open command prompt in 64bit instead of 32bit

  26 juin 2015, par Arvo Bowen

  I have been trying to get this script to work all day !

  Here are some facts about my situation...

  • I have a program named "ffmpeg.exe" in my "C :\Windows\System32\" folder.
  • I DO NOT have that program in my "C :\Windows\SysWOW64\" folder.

  Currently this is the script I have...

  Option Explicit
  
  
  
  Dim oFSO, oShell, sCommand
  
  Dim sFilePath, sTempFilePath
  
  
  
  Set oFSO = CreateObject("Scripting.FileSystemObject")
  
  
  
  sFilePath = "C:\test\in_video.mkv"
  
  sTempFilePath = "C:\test\out_video.mp4"
  
  
  
  sCommand = "%comspec% /k ffmpeg -n -i """ + sFilePath + """ -c:v copy -c:a copy """ + sTempFilePath + """"
  
  WScript.Echo sCommand
  
  Set oShell = WScript.CreateObject("WScript.Shell")
  
  oShell.Run sCommand, 1, True
  
  Set oShell = Nothing
  
  
  
  Set oFSO = Nothing

  If I run this script manually at a command prompt then it seems to work just fine. But if I let another app run it (for example in this case uTorrent), it runs the script as expected but when it tries to process the oShell.Run command it runs that in a 32bit environment ! Then I get this...
  

  If I try to open up a new command prompt (nothing special) i seems to default to a 64bit environment and then I can type "ffmpeg" and it shows me the help content as expected.

  So for some reason I can’t get the script to run applications (specifically CMD) in the 64bit environment. Anyone know how I can achieve this ?

  ---

  Update

  Seems that my script is in fact being ran in 32bit mode ! Even though the script title bar says "C :\Windows\System32\cscript.exe", which is a 64bit environment !!

  I used the following script to determine that it was running in a 32bit environment...

  Dim WshShell
  
  Dim WshProcEnv
  
  Dim system_architecture
  
  Dim process_architecture
  
  
  
  Set WshShell =  CreateObject("WScript.Shell")
  
  Set WshProcEnv = WshShell.Environment("Process")
  
  
  
  process_architecture= WshProcEnv("PROCESSOR_ARCHITECTURE") 
  
  
  
  If process_architecture = "x86" Then    
  
      system_architecture= WshProcEnv("PROCESSOR_ARCHITEW6432")
  
  
  
      If system_architecture = ""  Then    
  
          system_architecture = "x86"
  
      End if    
  
  Else    
  
      system_architecture = process_architecture    
  
  End If
  
  
  
  WScript.Echo "Running as a " & process_architecture & " process on a " _ 
  
      & system_architecture & " system."