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• ffmpeg : overlay video on top of a cropped video, map the overlay audio, cut the base video to the overlays length

  14 mars 2023, par roku

  I'm trying to overlay a video on top of a base video which is cropped to a shorts video format (standing phone). The overlayed video should be centered on top of the base layer. The base video's length should be reduced to the overlay's length. And I want to save only the overlay's audio.

  


  I've tried a bunch of stuff without much success. The current state of my ffmpeg command is this :

  


  ffmpeg -i overlay.mp4 -ss 00:00:00 -to <insert base="base"> -i base.mp4 -map 1:v:0 -map 1:a -vf "crop=ih*(9/16):ih" -crf 21 output.mp4&#xA;</insert>

  


  But this only gives me the cropped version of the base video. So my questions are :

  


  

  1. How can I figure out the base video's length ?

  


  2. How can I actually overlay (not map) other video on top of the base video ?

  


  3. How can I map the overlay's audio ? Since -map 1:a the base's audio and -map 0:a says : "Stream map '0:a' matches no streams. To ignore this, add a trailing ' ?' to the map."

  


  


  Any help is appreciated.

  


• How to concatenate and output various video bitrates and a standalone audio file ?

  5 octobre 2018, par Sasidharan S

  How to concatenate and output various video bitrates and a standalone audio file in ffmpeg ?

  My requirement is :

  1. I have 4 input files.
  2. Need to stitch all 4 files into single segment.
  3. Need output with four different video bit rates : 500k, 800k 1000k 1500k
  4. Along with that I need to extract only audio from stitched file.

  So my output will be 4 different video bitrate + 1 audio only file.

• Transcode HLS Segments individually using FFMPEG

  27 mai 2013, par rayh

  I am recording a continuous, live stream to a high-bitrate HLS stream. I then want to asynchronously transcode this to different formats/bitrates. I have this working, mostly, except audio artefacts are appearing between each segment (gaps and pops).

  Here is an example ffmpeg command line :

  ffmpeg -threads 1 -nostdin -loglevel verbose \
  
     -nostdin -y -i input.ts -c:a libfdk_aac \
  
     -ac 2 -b:a 64k -y -metadata -vn output.ts

  Inspecting an example sound file shows that there is a gap at the end of the audio :

  

  And the start of the file looks suspiciously attenuated (although this may not be an issue) :

  

  My suspicion is that these artefacts are happening because transcoding are occurring without the context of the stream as a whole.

  Any ideas on how to convince FFMPEG to produce audio that will fit back into a HLS stream ?

  ** UPDATE 1 **

  Here are the start/end of the original segment. As you can see, the start still appears the same, but the end is cleanly ended at 30s. I expect some degree of padding with lossy encoding, but I there is some way that HLS manages to do gapless playback (is this related to iTunes method with custom metadata ?)

  
  

  ** UPDATED 2 **

  So, I converted both the original (128k aac in MPEG2 TS) and the transcoded (64k aac in aac/adts container) to WAV and put the two side-by-side. This is the result :

  
  

  I'm not sure if this is representative of how a client will play it back, but it seems a bit odd that decoding the transcoded one introduces a gap at the start and makes the segment longer. Given they are both lossy encoding, I would have expected padding to be equally present in both (if at all).

  ** UPDATE 3 **

  According to http://en.wikipedia.org/wiki/Gapless_playback - Only a handful of encoders support gapless - for MP3, I've switched to lame in ffmpeg, and the problem, so far, appears to have gone.

  For AAC (see http://en.wikipedia.org/wiki/FAAC), I have tried libfaac (as opposed to libfdk_aac) and it also seems to produce gapless audio. However, the quality of the latter isn't that great and I'd rather use libfdk_aac is possible.