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• What's the difference with crf and qp in ffmpeg ?

  18 novembre 2016, par Nova

  After browsing around Google, I’ve came across this page about h264 encoding and discovered about qp. https://trac.ffmpeg.org/wiki/Encode/H.264

  My questions are : What are the differences with crf and qp ? Is it better to use qp over crf overall, or is it only if for using qp 0 for best lossless ? Does qp have a known sensible setting if it’s preferred ? So far, I know crf has the default value of 23 while 18 is a sensible preferred increase in quality, although I don’t understand why 18 wouldn’t be default if better sensible lossless. Lastly, would changing either of them cause incompatibility with non-ffmpeg players or just qp ?

  I’m converting from webm to mp4 by the way.

  I was going to test crf 23 and 18 and pick which is best but I can’t seem to find any concrete information on this comparison or about qp.

• FFMPEG Compilation and Video Thumbnail Issues [on hold]

  2 janvier 2016, par P. Paul

  I have compiled FFMPEg on a Linux, Centos machine according to the guide in here https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu , and the auto video thumbnail creation command in here https://trac.ffmpeg.org/wiki/Create%20a%20thumbnail%20image%20every%20X%20seconds%20of%20the%20video

  The problems are...

  1- When I use ffmpeg or ffmpeg -version command to check if ffmpeg has been installed I get the error message, "Command not found". But when I check for ffmpeg directory "~/ffmpeg_sources" is found and the machine says, "is a directory".

  2- Also, I did a test and upload video to the site to see if the video’s thumbnail will be automatically generated, but it didn’t show any thumbnail.

  Any help would be greatly appreciated.

  Thanks in advance !

• How concat files URL of S3 using Lambda, Ffmpeg

  4 juillet 2021, par Tính Ngô Quang

  I am trying to concat webm files into 1 file, Then upload file new video to S3
Using S3, ffmpeg/lambda-layer

  


  import subprocess
import shlex
import boto3

def lambda_handler(event, context):
    ffmpeg_cmd = "ffmpeg -safe 0 -f matroska concat"
    ffmpeg_cmd += " -i https://s3demo.s3.ap-northeast-1.amazonaws.com/archives/input/record/mask/ep_1.webm"
    ffmpeg_cmd += " -i https://s3demo.s3.ap-northeast-1.amazonaws.com/archives/input/record/mask/ep_2.webm"
    ffmpeg_cmd += " -c:v copy -af aresample=async=1:first_pts=0 -"

    command1 = shlex.split(ffmpeg_cmd)
    p1 = subprocess.run(command1, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    print(p1.stdout)
    print(p1.stderr)
    # resp = s3_client.put_object(Body=p1.stdout, Bucket=s3_source_bucket, Key=s3_destination_filename2)


  


  I get error message :

  


  


  concat : Read-only file system

  


  


  According to the article below, using directory storage but still the same error.
https://stackoverflow.com/a/47323443/2949104

  


  ffmpeg_cmd += " -vcodec copy -acodec copy /tmp/output.webm -y"