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• ffmpeg create thumbnail image of multiple images from video

  21 janvier 2018, par Michael Yousef

  So I want to create a thumbnail image that consists of multiple images from a single video. I’m looking to make them 4x8, and I want to spread out the images uniformly throughout the video.

  Ideally the final product should show 32 image captures, all downscaled to a reasonable size so they can fit on screen at the same time. Also, I’d like to have the final product have some overhead text like the video title, and I’d like to put the timestamp in the images as well.

  

  This is an example of what I want to do. The text at the top and the timestamp in the images. This one’s 6x4 and I want 4x8 but other than that it looks about what I want.

  I think ffmpeg probably has something to do this but I can’t seem to figure it out. I can generate individual screens but not collapse them into one. It’s also slower than programs I’ve used to do this in the past, not sure how they can do it as fast as they do. If I can’t get ffmpeg to do this, I’m open to using Python to accomplish this.

• Merging audio channels by FFmpeg libraries C++

  13 juin 2023, par Elija

  C/C++ project. There are several audio tracks with an individual number of channels. Each is processed using a avresampler. The avresampler converts all tracks to the same format. At the output of the avresampler, we get a set of channels from all audio tracks. Do the FFmpeg libraries have any standard means to merge all these audio channels into another set of audio channels using AVFrame::ch_layout to form a single audio track ? That is, no additional processing is required, except for copying channels buffers from several AVFrames of different audio tracks to new positions of one AVFrame according to the new layout and aligning the timestamps of different audio tracks, since different audio tracks can have audio frames of different sizes with different timestamps.

  


  For example, 1 audio track with 2 channels and 2 audio tracks with 6 channels will be merged into 16 channels with silence in the "missing" channels. Or 4 audio tracks with 2 channels merged into 8 channels. Etc...

  


  Is there a way to use a avresampler for this ? Or a avfilter ? Or something else ?

  


  Any source code or any reading source that can help me is welcome.

  


• Produce waveform video from audio using FFMPEG

  27 avril 2017, par RhythmicDevil

  I am trying to create a waveform video from audio. My goal is to produce a video that looks something like this

  

  For my test I have an mp3 that plays a short clipped sound. There are 4 bars of 1/4 notes and 4 bars of 1/8 notes played at 120bpm. I am having some trouble coming up with the right combination of preprocessing and filtering to produce a video that looks like the image. The colors dont have to be exact, I am more concerned with the shape of the beats. I tried a couple of different approaches using showwaves and showspectrum. I cant quite wrap my head around why when using showwaves the beats go past so quickly, but using showspectrum produces a video where I can see each individual beat.

  ShowWaves

  ffmpeg -i beat_test.mp3 -filter_complex "[0:a]showwaves=s=1280x100:mode=cline:rate=25:scale=sqrt,format=yuv420p[v]" -map "[v]" -map 0:a output_wav.mp4

  This link will download the output of that command.

  ShowSpectrum

  ffmpeg -i beat_test.mp3 -filter_complex "[0:a]showspectrum=s=1280x100:mode=combined:color=intensity:saturation=5:slide=1:scale=cbrt,format=yuv420p[v]" -map "[v]" -an -map 0:a output_spec.mp4

  This link will download the output of that command.

  I posted the simple examples because I didn’t want to confuse the issue by adding all the variations I have tried.

  In practice I suppose I can get away with the output from showspectrum but I’d like to understand where/how I am thinking about this incorrectly. Thanks for any advice.

  Here is a link to the source audio file.