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• What is the most efficient way of stacking two videos using ffmpeg ?

  4 octobre 2024, par technical_difficulty

  I want to stack two videos of a talk together vertically using ffmpeg. One shows the presentation (slides) and one shows the speaker. Since I want to do this for several talks, I'd like to do this in a more general way and as efficiently as possible. Most of the time the videos have different resolutions and aspect ratios.

  


  My current workflow is :

  


  


  1. Scale the video with the lower resolution up to match the resolution of the other video :
ffmpeg -i video1.mp4 -s 1920x1080 -c:a copy video1_upscaled.mp4

     


  


  2. Stack the two videos :
ffmpeg -i video1_scaled.mp4 -i video2.mp4 -filter_complex vstack=inputs=2 combined.mp4

     


  


  


  The videos are between one and two hours long and the commands do take a while to complete. Is there any way of saving some time ?

  


  Would it be faster to put black bars/borders around the smaller video instead of scaling it to the size of the other one ? Can the stacking be done in a more efficient way ? Would it help a lot if those two steps were combined into one ?

  


  Some information that might be relevant :

  


  

  • it's always exactly two videos to stack vertically, one above the other

  


  • the quality of the video is not incredibly important, both having the resolution of the video with the lower resolution would be perfectly fine

  


  • disk space is not an issue

  


  • the resolution and aspect ratio of the videos are known (use any for your example)

  


  • both videos have the same audio

  


  • both videos have the exact same length

  


  


• FPV-Camera Input in Black and White / losses Color on conversion with FFMPEG [closed]

  22 décembre 2023, par LyffLyff

  so we're working on our end-of-school project and it's an FPV-Drone with an Analogue Camera on it. Plan is to send the video feed to a Raspberry Pi running an RTMP-Server from where a Phone-Application can view the live Video of the camera.

  


  To convert this analogue Data from the camera we use a USB2.0 Grabber (this one).

  


  To create the RTMP Stream from the converted USB-Input we use FFMPEG with the following command :

  


  


  fmpeg -f v4l2 -input_format yuyv422 -i /dev/video0 -c:v libx264 -crf 20 -preset ultrafast -b:v 2000k -fflags nobuffer -rtmp_live live -f flv rtmp ://192.168.8.107:554/live/stream

  


  


  It works fine, but the main problems at the moment are :

  


  

  • the video is in Black and White
B&W Image Stream

  


  • the stream has a delay of 10-20s depending on the network

  


  


  When I'm using the official Software provided by the Reseller I had the same problem, but as soon as it set PAL/BDGHI in the Settings the colour was shown correctly :

  


  Settings and Color Image in official software

  


  the video is in Black and White

  


  Does anyone know what settings there are to correctly decode the feed from the Camera and send the video with the colour over RTMP ? I don't know if this is the right place to ask this question, but I'm running out of ideas and every single decoder I have tried apart from the ones I'm currently using does not work.

  


  Any help is greatly appreciated :)

  


• How to mix audio description track into stereo mix in FFMPEG or SOX

  4 mai 2022, par Overlook Motel

  I have a video file with a stereo mix. I have also been provided with an additional audio description track (a narration which describes what's happening on screen for visually-impaired audiences) as a mono WAV.

  


  I am trying to mix the two together, however the tricky part is adjusting the levels. The levels of the main mix should be dipped before and raised back again after each line of speech in the AD track.

  


  The company who produced the AD track have offered to do this for a fee, however I noticed that their fee is static regardless of the length of the film, so I assume it must be an automated process (if it involved a sound mixer in a studio, it'd be charged at a per minute rate).

  


  I'm wondering if it's possible to do this myself in FFMPEG.

  


  The AD track is cleanly recorded at a consistent level and is entirely silent in between the lines of narration. So imagine it would be in principle possible to determine where the main mix needs to go up and down.

  


  Would probably need to :

  


  

  1. Analyse the levels of the AD track and convert to a list of "fade down here", "fade up here" instructions.

  


  2. Apply that list of instructions to the main mix to create an intermediate.

  


  3. Mix together the intermediate with the AD track.

  


  


  The final step could be achieved with the amix filter, but I have little idea how to approach the first 2 steps.

  


  Does anyone know if this is achievable with FFMPEG ? I'd also be open to using other programs such as SOX.