Avoiding Audible Clicks When Concatenating Two MP4 Files with FFmpeg

Introduction

When working with multimedia files, there are situations where you need to concatenate multiple video files into one. This process is useful in many scenarios, such as combining intro and outro videos with a main video or merging several short clips into a single video. One popular command-line tool used for video operations, including concatenation, is FFmpeg. However, sometimes, an audible "click" sound may occur during the transition between the two videos. This article provides an in-depth explanation of the reasons for these clicks and demonstrates various methods to avoid them successfully.

Understanding the Cause of the Click Sound

The audible click is caused by the discontinuity between the two video files being concatenated. Specifically, it results from a difference in timestamps and codecs used between the two files.

Timestamp Discrepancy

Using FFmpeg's default concatenation method (-f concat -i list.txt -c copy out.mp4) relies on the input file timestamps. If the input files do not have the correct timestamp information, the output file may exhibit discontinuities in its audio and video streams.

Codec Mismatch

Another potential cause is differences in codecs or codec parameters between the input files, which may result in incompatibility between the video streams.

Solutions to Avoid Audible Clicks

You can apply various solutions to resolve the click sound during concatenation. This section will discuss different methods, such as:

• Setting correct timestamps
• Re-encoding audio or video streams
• Utilizing filter_complex and concat demuxer

Setting Correct Timestamps

Before concatenating the files, ensure their timestamps are set with accuracy. You can use the setpts and setdar filters inside FFmpeg to adjust the video streams. For instance, you can use the following commands to set the timestamps for the files input1.mp4 and input2.mp4:

Now, concatenate the modified files as follows:

Re-encoding the Audio or Video Streams

If the codecs do not match, you can re-encode the input video streams or audio streams with FFmpeg using the -c flag for the desired codec. Re-encoding may require more computation, but it ensures compatibility between the streams.

Utilizing filter_complex and Concat Demuxer

You can take advantage of FFmpeg's filter_complex capability in conjunction with the concat demuxer to achieve higher control over input video and audio streams.

Carefully addressing the timestamp discrepancies and codec mismatches can significantly reduce or eliminate audible clicks during concatenation using FFmpeg. By trying the solutions presented above, you will effectively manage these issues and maintain a smooth and seamless combined video.

References

• FFmpeg documentation
• FFmpeg wiki: Concatenate
• Super User: FFmpeg concat filter – clicking sound