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• ffmpeg - How to (programmatically) copy a stream's side data ?

  25 mars 2021, par waldenCalms

  My app is a tag editor (eg ID3) written in Swift for macOS. I'm using ffmpeg as my library to perform the tag editing. When the user is done editing, the app should save the changes to (essentially) a modified copy of the original file. I'm able to copy everything I need (from input -> output file) EXCEPT "side data".

  


  In other words, I'm doing the programmatic equivalent of :

  


  ffmpeg -i input.mp3 -metadata key1=value1 -metadata key2=value2 -codec copy output.mp3


  


  So, output.mp3 must be identical to input.mp3, except for the few metadata changes made by the user.

  


  What I have working so far

  


  I'm able to copy the audio stream and all associated metadata (tags), as is, from input.mp3 to output.mp3.

  


  The problem

  


  My input.mp3 happens to have some side data (see below), which does not get copied over to output.mp3. How to copy side data ? To be honest, I don't even know what side data is, and the documentation is not very helpful.

  


  ffprobe gives the following output (snippet) for the input.mp3's side data that looks like :

  


  Side data:
      replaygain: track gain - -9.200000, track peak - unknown, album gain - unknown, album peak - unknown,


  


  I want THIS ^ to get copied over to output.mp3, but it does not :(

  


  Relevant code snippet (format context initialization code omitted for conciseness)

  


  let inAudioStream = inFormatContext!.pointee.streams.advanced(by: Int(audio_stream_index)).pointee!.pointee&#xA;var outAudioStream = outFormatContext!.pointee.streams.advanced(by: Int(audio_stream_index)).pointee!.pointee&#xA;            &#xA;/* Free existing side data*/&#xA;            &#xA;for i in 0..* Copy side data if present */&#xA;            &#xA;if let srcSideData = inAudioStream.side_data {&#xA;                &#xA;    let rawPtr: UnsafeMutableRawPointer? = av_mallocz_array(Int(inAudioStream.nb_side_data),&#xA;                                                            MemoryLayout<avpacketsidedata>.size)&#xA;                &#xA;    outAudioStream.side_data = UnsafeMutablePointer<avpacketsidedata>(OpaquePointer(rawPtr))&#xA;    outAudioStream.nb_side_data = inAudioStream.nb_side_data&#xA;                &#xA;    for i in 0..(OpaquePointer(data))&#xA;    }&#xA;}&#xA;            &#xA;status = avformat_write_header(outFormatContext, nil)&#xA;</avpacketsidedata></avpacketsidedata>

  


  I got this logic from this page. Is this ^ the right way to copy a stream's side data to the corresponding stream in the output file ? If not, how to do it ?

  


  I have also tried the following functions with no luck :

  


  av_stream_new_side_data(...)
av_stream_add_side_data(...)


  


  Please ask for details if required, and I will provide them. Thanks very much !

  


• How to save ffmpeg stream with datetime

  18 janvier 2013, par user1800256

  I would like to write an output format from a ffmpeg encode line to save the stream in a SD card with date and hour.

  To simplify the question I write the following (just ignore the extras) :

  import subprocess, sus, os, datetime, time
  
  from subprocess import Popen, PIPE
  
  
  
  def call_command(command):
  
      subprocess.Popen(command.split('  '))
  
  
  
  call_command('ffmpeg -f video4linux2 -y -s qvga -r 24 -i /dev/video0 \
  
                -vcodec mpeg2video /home/pi/webcam_+%Y/%m/%d_at_%H:%M:%S.mpg')

  I also tried another solutions like define firstly the filename and call it from the ffmpeg line but it doesen't work.

• FFMPEG CPU encoding speed

  22 janvier 2020, par natloz

  I would like to increase the speed of encoding videos. Thou having issue with it...

  This is my CPU : Intel(R) Xeon(R) CPU E5-2603 v4 @ 1.70GHz
  OS : Windows 10 PRO 64bit

  I don’t have a graphics card.

  This is the script I’m using for current video encoding :

  ffmpeg -y -re -i o.mov -vf subtitles=SUBS.srt -s 1920x1080 -r 25 -pixel_format yuv420p -aspect 16:9 -top 1 -qp 0 -c:v libx264 -b:v 600000 -minrate 600000 -maxrate 600000 -x264opts bitrate=6000:vbv-maxrate=6000:vbv-bufsize=400:ratetol=400:bitrate=6000:vbv-init=800:force-cfr=1 -g 33 -bf 3 -muxrate 6.5M -flags cgop+ilme+ildct -c:a mp2 -ac 2 -ar 48k -b:a 192k -f mpegts out.mpeg

  The current speed I’m getting is : speed = 1x.

  How can I force my CPU to work at full speed ?