ss will define the starting point to cut To cut either stream, you can use -ss -t before each of the -i 'file.ext'. If your audio stream is for example longer than the video stream, you have to cut it or otherwise you will have the last video frame as a still image and audio running. Since I am not allowed to write comments to the first answer with my reputation, an addendum here, because I had this problem when encoding webms. The -map option makes ffmpeg only use the first video stream from the first input and the first audio stream from the second input for the output file. If your input video already contains audio, and you want to replace it, you need to tell ffmpeg which audio stream to take: ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 output.mp4 If your output container can handle (almost) any codec – like MKV – then you can simply copy both audio and video streams: ffmpeg -i video.mp4 -i audio.wav -c copy output.mkv If your audio or video stream is longer, you can add the -shortest option so that ffmpeg will stop encoding once one file ends. See the FFmpeg Wiki: AAC Encoding Guide for more info. You can use any other desired audio codec if you want. The above command transcodes the audio, since MP4s cannot carry PCM audio streams. Here, we assume that the video file does not contain any audio stream yet, and that you want to have the same output format (here, MP4) as the input format. It should be something to the effect of: ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac output.mp4 See this example, taken from this blog entry but updated for newer syntax. We are telling ffmpeg:ĭon't use the streams directly from the input files, instead use these data streams created by a filtergraph.Merging video and audio, with audio re-encoding That names look familiar? Its what we labeled the streams created from the concat filter. Lastly, we need to explicitly tell ffmpeg what streams of data to map to the output being written to the file, using the -map option Here, we are calling the newly created video stream outv and the audio stream outa, we need these later when using the -map flag on the output Next, we label the streams of data created by the filter using the bracket syntax: V=1 indicates each input source has only one video stream and to write only one video stream out as outputĪ=1 indicates each input source has only one audio stream and to write only one audio stream out as output N=2 is specifying there are two input sources Now after we declared what streams we are using, we have a normal filter syntax: Those of us with experience in programming will understand why the index starts at 0 and not 1 Use the video stream of the first input source, use the audio stream from the first input source, use the video stream from the second input source, and use the audio stream from the second input source. Unlike using filters normally with ffmpeg using -vf or -af, when using a complex filtergraph, we have to tell ffmpeg what streams of data we are operating on per filter. This one is probably pretty confusing, so let me explain the complex filtergraph syntax: Lets look at the examples, first the concat demuxer approach:Įnter fullscreen mode Exit fullscreen mode The syntax is hard to understand if you've never written complex filtergraphs before for ffmpeg.This will cause a transcoding to a occur, so it takes time and may degrade quality.This method can concat videos with different encodings.Using a complex filtergraph with the concat filter.

There are very few encodings that can do this, the only one I've used the is MPEG-2 Transport Stream codec (.ts).There are some encodings that support file level concatenation, kinda like just using cat on two files in the terminal.Using file level concatenation approach.This method only works if the files have the same video and audio encoding, otherwise artifacts will be introduced.This method is very fast as is avoids transcoding.There are three methods I have found thus far: It turns out, that is rather simple to do with ffmpeg. I have found it very useful to concatenate multiple video files together after working on them separately.

Python ffmpeg merge audio and video