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• ffmpeg : Encoding a single live video stream into different resolutions and keeping them in sync

  15 mai 2020, par Almus

  I'm using NGINX as a simple HLS live video server. Sending an rtmp stream into the server, transcoding it into three different resolutions for delivery using HLS to users with different bandwidth limits.

  



  The problem I'm having is that when I take the 1080p 30fps input transcode it down to 480p and 720p then split it into chunks with HLS the segments from the two transcoded outputs are not in sync with the copied full resolution stream.

  



  here is what I am doing now :
exec FFmpeg on the source rtmp stream :

  



  exec ffmpeg -i rtmp://127.0.0.1:1935/live/$name
     -c:v libx264 -c:a aac -b:a 128k -vf "scale=-2:720" -vsync 1 -copyts -start_at_zero -sws_flags lanczos -r 30 -g 30 -keyint_min 30 -force_key_frames "expr:gte(t,n_forced*1)" -tune zerolatency -preset ultrafast -crf 28 -maxrate 2096k -bufsize 4192k -threads 16 -f flv rtmp://localhost:1935/show/$name_720
     -c:v libx264 -c:a aac -b:a 96k -vf "scale=-2:480" -vsync 1 -copyts -start_at_zero -sws_flags lanczos -r 30 -g 30 -keyint_min 30 -force_key_frames "expr:gte(t,n_forced*1)" -tune zerolatency -preset ultrafast -crf 28 -maxrate 1200k -bufsize 2400k -threads 16 -f flv rtmp://localhost:1935/show/$name_480
     -c copy -vsync 1 -f flv rtmp://localhost:1935/show/$name_src;


  



  Then take the results and segment them for HLS

  



  hls on;
hls_path /var/www/live-adapt;
hls_nested on;
hls_fragment 1;
hls_playlist_length 30;

hls_fragment_naming system;

hls_variant _480 BANDWIDTH=1200000; # Medium bitrate, SD resolution
hls_variant _720 BANDWIDTH=2048000; # High bitrate, HD 720p resolution
hls_variant _src BANDWIDTH=4096000; # Source bitrate, source resolution


  



  This is working except the streams are not in sync which causes issues if the end-users need to (or choose to) switch between streams.
Example :

  



  Sequence number 510 was not everywhere in sync:
PTS 510.7 for https://fqdn/live-adapt/c5d7ddb2-5562-4bd3-9e06-df9fa6e8ff06_480/1589521352937.ts
PTS 510.7 for https://fqdn/live-adapt/c5d7ddb2-5562-4bd3-9e06-df9fa6e8ff06_720/1589521352933.ts
PTS 511.699 for https://fqdn/live-adapt/c5d7ddb2-5562-4bd3-9e06-df9fa6e8ff06_src/1589521353752.ts


  



  I would love any advice or suggestions.

  


• Removing hidden characters from text file with tr while keeping latin-2

  16 mai 2020, par philk

  I have some text files with hidden characters and I'm able to remove them with this command :

  



  tr -cd '\11\12\15\40-\176' < initial_file > final_file


  



  This command would be perfect if I could keep latin-2 characters. I can't find info about 6 digit octal in tr man page. How can add characters with octal value like \305\237 or \303\256 to that tr command ?

  



  I need to keep this list :

  



  \304\202 Ă
\304\203 ă
\303\216 Î
\303\256 î
\303\202 Â
\303\242 â
\305\236 Ş
\305\237 ş
\305\242 Ţ
\305\243 ţ


  



  My system locale is en_US.UTF-8.
I have subtitles from several translators and I burn them onto video with a ffmpeg script. All went fine until some of the translators delivered subtitles with a little problem : in VLC I don's see it but after I burn with ffmpeg, an unwanted character is in front of every line. I can't copy that character and remove it with sed since is burned in the output video. If I run cat -v on that subtitle I see M-bM-^@M-^N in front of every line.

  


• Recursively Convert FLAC to MP3 Keeping All Metadata and Located in Same Directory

  6 juin 2020, par charlesstricklin

  I've got ffpeg installed on my Windows 10 PC and I'd like to recursively convert .flac music into .mp3 within the same directory (by that I mean the .flac file and the .mpg file end up in the same folder) and I'll be the first to admit I'm just a beginner to both ffmpeg and the CLI, so I'm a newbie there.

  



  I've been looking at Recursively Converting FLAC to MP3 Using FFmpeg While Maintaining Metadata and Directory Structure on Windows as a possible answer to my question, but I do not want to copy from one volume to another.

  



  Just to avoid confusion, my highest directory is C :\Users\User\Downloads\Music\ and I'd like to convert several artist/band's tracks from .flac to .mp3 within the same directory. C :\Users\User\Downloads\Music\1st Artist\1st CD\1st Track.flac would be converted to C :\Users\User\Downloads\Music\1st Artist\1st CD\1st Track.mp3, C :\Users\User\Downloads\Music\2nd Artist\1st CD\1st Track.flac would be converted to C :\Users\User\Downloads\Music\2nd Artist\1st CD\1st Track.mp3 and so on.

  



  Would someone clue me in on the best way you know of to accomplish that from the CLI, please ?