Configure Video Stream Count in FFmpeg Concat Filter

This article explains how to configure the video stream count in the FFmpeg concat filter. You will learn how to use the filter’s parameters to define the number of input segments, specify the video and audio stream counts, and write a correct command-line syntax for seamless video concatenation.

The FFmpeg concat filter is used to join multiple video and audio segments back-to-back. To configure the stream counts, you must define three key parameters inside the filter: n, v, and a.

Understanding the Parameters

• n (Segments count): Specifies the number of input segments you want to join together. The default value is 2.
• v (Video streams count): Specifies the number of output video streams per segment. The default value is 1.
• a (Audio streams count): Specifies the number of output audio streams per segment. The default value is 0.

If your source files contain one video track and one audio track, you must explicitly set v=1 and a=1.

Command Syntax and Structure

The basic syntax for the concat filter in a complex filtergraph (-filter_complex) is:

[input_0][input_1]...[input_N]concat=n=N:v=V:a=A[out_video][out_audio]

Practical Example

To concatenate three separate video files (each containing 1 video stream and 1 audio stream) into a single output file, use the following configuration:

ffmpeg -i input1.mp4 -i input2.mp4 -i input3.mp4 -filter_complex \
"[0:v][0:a][1:v][1:a][2:v][2:a]concat=n=3:v=1:a=1[outv][outa]" \
-map "[outv]" -map "[outa]" output.mp4

Breakdown of the Configuration:

1. -i input1.mp4 -i input2.mp4 -i input3.mp4: Loads the three input files.
2. [0:v][0:a]: Selects the video and audio streams of the first file (index 0). This is repeated for index 1 and index 2.
3. concat=n=3: Tells FFmpeg to expect 3 input segments.
4. v=1: Tells FFmpeg that each segment has 1 video stream to be joined into 1 output video stream.
5. a=1: Tells FFmpeg that each segment has 1 audio stream to be joined into 1 output audio stream.
6. [outv][outa]: Names the resulting concatenated video and audio output pads.
7. -map "[outv]" -map "[outa]": Instructs FFmpeg to write the processed streams to the final container (output.mp4).