cretueusebiu / ffmpeg-seek-bug

ffmpeg-seek-bug

When converting an audio file in chunks using -ss and -t, ffmpeg adds few milliseconds of silence at the end causing a gap when concatenating the chunks back.

# Convert the first 5 seconds of audio
ffmpeg -y -ss 0 -t 5 -i input.mp3 -codec:a flac chunk-1.flac

# Convert the next 5 seconds of audio
ffmpeg -y -ss 5 -t 5 -i input.mp3 -codec:a flac chunk-2.flac

# Concatenate both chunks
ffmpeg -y -safe 0 -f concat -i input.txt -codec:a flac output.flac

Now play output.flac and you'll notice a gap between seconds 4 and 5.

In the screenshot bellow you can see the original input and the chunks as well as the final output with a gap between the two chunks.

Using atrim instead of -ss and -t fixes this problem only for the flac codec.

# flac codec
ffmpeg -y -i input.mp3 -af atrim=0:5 -codec:a flac chunk-1.flac
ffmpeg -y -i input.mp3 -af atrim=5:10 -codec:a flac chunk-2.flac
ffmpeg -y -safe 0 -f concat -i input-flac.txt -codec:a flac output.flac

# aac codec (or libfdk_aac)
ffmpeg -y -i input.mp3 -af atrim=0:5 -codec:a aac chunk-1.m4a
ffmpeg -y -i input.mp3 -af atrim=5:10 -codec:a aac chunk-2.m4a
ffmpeg -y -safe 0 -f concat -i input-aac.txt -codec copy output.m4a

No gap between the chunks when listening output.flac but output.m4a still has the same problem.