For clips with different codecs, use FFmpeg’s concat filter and re-encode the result. A playlist file only sets clip order; it does not make incompatible codecs match. The concat demuxer with -c copy is appropriate only when the inputs have compatible streams and parameters.
Choose the right FFmpeg concatenation method
| Approach | What it does | When to use it | Trade-off |
|---|---|---|---|
Concat demuxer with -c copy |
Joins packets without decoding or encoding them. | Inputs have the same streams, codecs, time bases, and compatible parameters. | Fast and avoids generation loss from re-encoding, but cannot convert codecs or normalize mismatches. |
| Concat filter with encoding | Decodes segments, concatenates their audio/video, then encodes the output. | Inputs use different codecs or need normalization before joining. | Allows filtering and format conversion, but encoding takes time and may affect quality. |
FFmpeg’s FAQ says of the concat filter: “This operation is recommended if you need to re-encode.” Read the FFmpeg concat FAQ.
Inspect the clips before building the filter
Check each file’s streams and properties before choosing the filter graph. In particular, confirm that every clip has the video and audio streams the example below expects, and note differences in resolution, pixel format, frame rate, sample rate, and channel layout.
ffprobe -hide_banner clip-one.mp4
ffprobe -hide_banner clip-two.movThe example filter graph assumes every input contains one video stream and one audio stream. If a clip lacks audio, this graph will not work as written: create silent audio for that segment or build separate audio and video concatenations. Other differences may require filters such as scale, setsar, fps, or aresample. Normalize deliberately rather than forcing a frame rate or aspect ratio without checking the source.
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Create the playlist file
A concat playlist is a plain-text manifest. Put one file entry per line, in the order you want the clips to appear, and save it as inputs.txt:
file 'clip-one.mp4'
file 'clip-two.mov'
file 'clip-three.mkv'Use paths relative to the playlist’s directory where possible. The manifest controls order; it does not reconcile differences among the files.
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Use the concat filter for different codecs
For two clips that each contain one video and one audio stream, this is a starting point for decoding, concatenating, and encoding an MP4:
ffmpeg -i clip-one.mp4 -i clip-two.mov
-filter_complex "[0:v:0][0:a:0][1:v:0][1:a:0]concat=n=2:v=1:a=1[v][a]"
-map "[v]" -map "[a]"
-c:v libx264 -crf 18 -preset medium -pix_fmt yuv420p
-c:a aac -b:a 192k -movflags +faststart output.mp4The filter inputs are listed in segment order: video then audio for the first clip, followed by video then audio for the second. The output labels [v] and [a] are mapped to the encoded video and audio streams. This illustrative command is not universal or guaranteed to work unchanged on arbitrary files. If streams or parameters differ, adapt the filter graph after inspecting the inputs.
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The command encodes video as H.264 with CRF 18 and the medium preset, and audio as AAC at 192 kbps. CRF is a quality-oriented encoding setting rather than a fixed output bitrate; the resulting bitrate depends on the content. Re-encoding creates a new generation, so retain the original files if you may need to make a different output later.
When the concat demuxer and stream copy are suitable
If the clips already have compatible streams—including codecs and time bases—you can use the demuxer with stream copy. The concat demuxer’s requirements are stricter than simply having files that play successfully on their own. File duration metadata is used to adjust timestamps for the next file, so inaccurate durations can cause artifacts.
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ffmpeg -f concat -safe 0 -i inputs.txt -c copy joined.mp4Use -safe 0 only when the playlist contents are trusted; it permits paths that would fail the demuxer’s safe-path checks. Most importantly, do not use -c copy as the solution to mixed codecs. Stream copy copies packets as they are and does not decode or transform one codec into another. See FFmpeg’s concat demuxer documentation and stream-copy documentation.
Prepare the output for YouTube
YouTube’s recommended upload settings list MP4, H.264 video, progressive scan, and AAC-LC audio, among other recommendations. Its SDR video bitrate recommendations include 8 Mbps for 1080p at standard frame rates and 12 Mbps for 1080p at high frame rates. These are recommendations, not mandatory minimums. YouTube advises uploading at the same frame rate as the recording; check the current guidance and the actual source properties before setting output filters or bitrates.
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For this example, H.264, AAC, and MP4 are aligned with common YouTube upload recommendations, but -crf 18 does not guarantee an 8 or 12 Mbps bitrate. If you need to target a bitrate, choose an encoding strategy based on the sources and the desired output, then inspect the resulting file. YouTube’s page also covers color-space and audio recommendations: YouTube recommended upload encoding settings.
Troubleshoot common failures
- The demuxer reports mismatched streams or parameters: The files are not compatible for packet-level concatenation. Use the concat filter and encode, or normalize inputs first.
- The filter reports missing audio or video: The example assumes one of each stream in every input. Identify the missing stream and supply silent audio where appropriate or build separate audio and video graphs.
- The output has a jump, glitch, or timing problem at a boundary: Compare stream properties and durations. In demuxer workflows, inaccurate recorded durations can shift subsequent timestamps. For filtered output, normalize relevant timing or format differences as needed.
- Resolution, aspect ratio, or frame rate changes unexpectedly: Check each input with
ffprobe. Apply deliberatescale,setsar, orfpsfilters only when the output needs a common format. - Audio is distorted, silent, or changes level: Check for missing streams, sample-rate differences, and channel-layout mismatches; consider
aresampleand a graph that handles each input’s actual layout. - The output is not accepted or looks wrong after upload: Verify the encoded file’s container, codecs, scan type, frame rate, aspect ratio, and audio. Compare them with YouTube’s current upload recommendations rather than assuming a successful FFmpeg exit guarantees the intended presentation.
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