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• For modifying MPEG-2 Part 4 video, which is the easiest library/approach can I use ?

  17 décembre 2015, par liamzebedee

  I’m trying to implement a video watermarking system which modifies a subset of individual pixels (i.e. the RGB values at sets of x,y). The base use case would be modifying an MP4, which consists of modifying the contained MPEG-2 Part 4 Video stream.

  I’ve done some research, and have found that it isn’t as simple as just modifying the raw frames, as the ubiquitous P-frames and B-frames rely on compressing the output by only storing the differences between frames.

  I’m relatively technology-agnostic, I just want to find a solution. Which library/framework should I use (seems like ffmpeg for now) and which approach do I take ?

• Player downloads all moof part of a fragment mp4 file before playing

  28 mars 2023, par happyz90

  I converted a mp4 to fragment mp4 with the following command :

  


  ffmpeg -i ./input.mp4 -y -b:a 32k -vcodec libx265 -b:v 320k -bufsize 320k -tag:v hvc1 -color_primaries bt709 -color_trc bt709 -colorspace bt709 -c:a libfdk_aac -profile:a aac_he_v2 -movflags faststart+frag_keyframe+empty_moov+dash+global_sidx -chunk_duration 500000000 -max_muxing_queue_size 1024 ./output.mp4


  


  But when playing, the player send many http requests to download all the moof part :

  


  

  


  

  


  But I think in normal case the player only need to download the head part of the video file to play.

  


  So is there anything wrong with my ffmpeg parameters ? Please help me. Thank you.

  


• Download a part of youtube video using a powershell script

  26 octobre 2024, par Nguyễn Đức Minh

  I'm writing this Powershell script :

  


  $URL = "https://www.youtube.com/watch?v=KbuwueqEJL0"
$from = 00:06:15
$to = 00:09:17

$cmdOutput = (youtube-dl --get-url $URL) 

ffmpeg -ss $from -to $to -i  -ss $from -to $to -i  output.mkv


  


  This script's purpose is to download a part of a Youtube video. I've set the variable $URL to specify the Youtube URL, while $from and $to is the start and end time of the part I want to download.

  


  $cmdOutput is used to output the stream URL. The output would have two lines : the first one is the URL for the video stream, while the second one is the audio stream URL.

  


  Currently, I don't know how to use the output as a variable and specify the line number of $cmdOutput to put it into the correct stream. I guess and would be replaced by something like $cmdOutput[line 1], and $cmdOutput[line 2], though I know that those are incorrect.

  


  I've consulted this answer, and it is handy for me to write this script. I've also read Boris Lipschitz's answer on how to do the same thing with Python, but his answer does not work.

  


  In that script, the -ss flag inputs the seeking point, and the -t <duration></duration> flag tells FFmpeg to stop encoding after the specified duration. For example, if the start time is 00:02:00 and the duration is 00:03:00, FFmpeg would download from 00:02:00 to 00:05:00, which is not the expected outcome. For some reason, his Python script skips the first 5 seconds of output, even if I replace the -t flag with -to . I've tried to edit his script, but it does not work unless you explicitly specify the time for both video and audio stream, as well as their respective stream URL.