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• Use ffmpeg to concatenate a video and a timelapse

  26 décembre 2022, par tudors

  Input 1 : I used my phone to record a 25 fps movie with 1920x1080 resolution. There is sound.

  


  Input 2 : I used ffmpeg to create a timelapse movie i.e. 25 fps made out of 1920x1080 JPEGs. There is no sound.

  


  When I tried to concatenate them however, the result was a mess : It seems some fine detail is not matching between the two inputs, because the resulting video squishes the time lapse down to just 1 frame at the end.

  


  I have also tried this by first removing sound from video 1, so that both videos are soundless, and this does not give a different result.

  


  How can I tell ffmpeg that the two inputs are not incongruent, so as to achieve a correct 25 fps 1920x1080 video using all the frames from both inputs ?.

  


• FFmpeg segmentation and transcoding missing frames

  15 décembre 2022, par Davidec0018

  I code videos for hobbies and have a decent understanding of ffmpeg and mkvmerge. I prefer to encode video when my computer is on for other things as well, so I recently looked for a way that I could resume encoding after the computer was turned off.

  


  I tried a virtual machine, saving the whole state and it seems to work very well, but the performance is very slow and with the same settings the encoding time is much longer than normal.

  


  I then tried to divide the starting video into several segments, so as to resume from the appropriate segment after restarting the computer.

  


  I tried to do this with ffmpeg :

  


  ffmpeg -i input -map 0:v:0 -c copy -f segment -segment_time 300 -reset_timestamps 1 segment%03d.mkv


  


  But also with the mkvtoolnix gui.

  


  Both operations provide an excellent result.Trying to merge the segments into one video, with ffconcat or mkvtoolnix the result is perfect.

  


  The problem arises when segments are encoded. I use a simple script based on slow preset for every segment in loop (I use both windows and linux) :

  


  ffmpeg -i input.mkv -threads 0 -map 0 -c:a copy -c:s copy -preset slow -pix_fmt yuv420p10le -c:v libx265 -x265-params crf=18:bframes=8:aq-mode=2:aq-strength=1.0 output.mkv


  


  Putting them together in the same way, the video also looks quite good, and with the naked eye you don't notice the passage of the various segments, but analyzing them with ffmpeg I notice that the individual segments have slightly shorter durations and a different number of frames, even 2 or 3 less. When putting together very long videos, you notice even 2 seconds of difference with the original, which also causes the audio and subtitles to go into desynch.

  


  I know the problem has to do with keyframes, timestamps and stuff like that. But I don't understand why. FFmpeg, as well as mkvmerge should split the video exactly where the keyframes are, about 300 seconds apart, so as not to mess up the video structure and allow for good encoding and reassembling.

  


  The problem is just encoding with ffmpeg that removes some frames from the original segments. Sometimes I noticed during the encoding of some segments the following error code, or maybe warning, because the encoding worked anyway :

  


  [hevc @ 0x55758bf92dc0] First slice in a frame missing.
    Last message repeated 6 times
[hevc @ 0x55758c2000c0] First slice in a frame missing.


  


  I've read every discussion about it on the net, I've tried to segment both with mp4 and mkv format, with and without audio, but the problem remains. Where am I doing wrong ?

  


• FFMPEG Audio stream/layer and SRT from one mkv to an other

  13 juillet 2022, par kormorfor

  I have an FFMPEG question for you !

  


  Problem :

  


  I have 2 files(x265)

  


  01.mkv with multiple audio steams and multiple subtitles (with exactly named layers)

  


  02.mkv with multiple audio steams and multiple subtitles (with exactly named layers)

  


  I would like to add specific audio layer(GER) and specific subtitle(GER)
from 02.mkv to 01 mkv at the same time if it is possible.
(The metadata positions almost always random in file 02.mkv so I can't say it is "-map 0:s:2 for ger subtitle"...)

  


  I have already searched and tried multiple solutions ...

  


  This kind of worked with multiple steps but loses audio and subtitle metadata(Title) during process.

  


  German audio layer extract from 02.mkv to aac

  


  ffmpeg -i 02.mkv -map 0:a:m:language:ger 02.aac


  


  German subtitle layer extract from 02.mkv to srt

  


  ffmpeg -i 02.mkv -map 0:s:m:language:ger 02.srt


  


  Adding extracted audio to 01.mkv

  


  ffmpeg -i 01.mkv -i 02.aac -map 0 -map 1 -codec copy outputfinall_1.mkv


  


  Adding extracted srt to 01.mkv none of this works

  


  1.)

  


  ffmpeg -i 01.mkv -i 02.srt -c copy -c:s mov_text outputfinall_2a.mkv


  


  BUG : Subtitle encoding currently only possible from text to text or bitmap to bitmap

  


  2.)

  


  ffmpeg -i 01.mkv -i 02.srt -map 0 -map 1 -codec copy outputfinall_2b.mkv


  


  works but does not show subtitles while playing only that is there.

  


  Please if you can help I would like a less jumbled mess code for this problem.
With keeping the metadata (titles) of the moved audio stream and subtitle.

  


  Thank you for your time !