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Generate a countdown slate
A countdown is an overlay whose value changes with the slate’s elapsed time. A holding screen can be a solid-color background, a still image, or a background with a logo. In either case, make the interstitial a video segment with an explicit duration, then place it between the video segments.
This illustrative command creates a 10-second, 1920×1080, 30 fps black slate with centered text:
ffmpeg -f lavfi -i "color=c=black:s=1920x1080:r=30:d=10"
-vf "drawtext=fontfile=/path/to/font.ttf:text='Next video in %{eif\:max(0\,10-t)\:d}':fontsize=64:fontcolor=white:x=(w-text_w)/2:y=(h-text_h)/2"
-t 10 slate.mp4Replace /path/to/font.ttf with a font file that exists on the machine. The example illustrates the filter expression and is not a tested, universal command: escaping can vary with the operating system, shell, and FFmpeg build. drawtext requires a build with libfreetype; font-name lookup may also depend on build options. See the FFmpeg Project’s filters documentation for drawtext, the color source, and filter-expression examples.
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Decide what the numbers mean
The expression uses the slate’s local elapsed time, not the wall clock. Decide whether the first displayed value should be 10 or 9, whether values update at each whole second, and whether zero should appear for a full second. The example clamps the expression at zero, but the exact visible timing depends on frame rate and expression evaluation.
Use a still image or logo instead
You can use a still image as the slate or composite an image over a generated background with overlay. If the image is a separate input, make sure it lasts through the entire slate and that its timestamps align with the background. FFmpeg’s overlay documentation notes that inputs are consumed in timestamp order; offset initial timestamps may need resetting with setpts=PTS-STARTPTS. The loop video filter can repeat frames, but the finished segment still needs a deliberate duration or stop condition. See FFmpeg’s filter documentation.
Choose how to join the slate and videos
| Method | Use it when | Important constraint |
|---|---|---|
| Concat filter | Inputs need decoding, normalization, or re-encoding—for example, when clip dimensions or frame rates differ. | Build a filtergraph for every segment and encode the joined output. Include audio handling if you need continuous audio. |
| Concat demuxer | All files, including the slate, already have matching stream layouts and compatible codecs and time bases, and avoiding re-encoding matters. | Duration metadata affects where the next file begins; inaccurate durations can cause timestamp artifacts or gaps. |
The FFmpeg Project’s concat demuxer documentation states: “All files must have the same streams (same codecs, same time base, etc.).” Read the formats documentation and the FFmpeg FAQ on concatenating media before choosing. Do not assume that ordinary MP4 files can be joined with -c copy when their streams differ.
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Use the concat filter when the inputs differ
The filter approach decodes the inputs, lets you normalize them to compatible dimensions, frame rates, pixel formats, sample rates, and channel layouts, and then encodes the combined output. It is more adaptable for unlike clips and a generated slate, at the cost of encoding. The FAQ recommends the concat filter when re-encoding is needed. A correct command depends on the actual input streams and the intended output, so inspect the files and construct a filtergraph for those streams rather than applying a generic copy command.
Use the concat demuxer only when streams match
The demuxer reads a text playlist and presents files sequentially. Check that each file—including the slate—has compatible streams, codecs, and time bases. Inspect duration metadata as well: the demuxer uses file durations to place subsequent media, so an incorrect duration can shift timestamps or create a gap. Consult the concat demuxer documentation for its requirements and behavior.
Plan audio and output timing
Choose what listeners should hear during the interstitial. If the outgoing stream needs an audio stream throughout, give the slate matching audio (silence is one option) or construct the filtergraph to maintain continuous audio. A slate with no audio can create a stream-layout mismatch for the demuxer or an audio gap in the output, depending on the join method and muxer.
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- Check the audio stream layout across every segment, including the slate.
- For a filtergraph, explicitly map the intended video and audio outputs.
- Confirm the destination’s required video and audio codecs, pixel format, frame rate, and muxer.
- For image inputs or other timestamp offsets, verify alignment; use
setpts=PTS-STARTPTSwhere appropriate.
FFmpeg’s documentation covers complex filtergraphs and stream mapping. A finite playlist rendered to RTMP, HLS, or DASH is not the same problem as a persistent live process that must wait for new clips and keep a connection open indefinitely. There is no single universal queue or scheduling design for every protocol: the command depends on the output protocol, FFmpeg build, input media, audio policy, and what should happen when the playlist ends.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot common failures
drawtext is unavailable or reports a font error
The installed FFmpeg may lack libfreetype support, or the specified font path may not exist. Check the installed build and use an available font file; font-name selection alone may rely on fontconfig support. The filters documentation describes the filter and its dependencies.
The countdown text or punctuation is malformed
Filter expressions pass through both shell and filtergraph parsing, so colons and commas may need escaping. Adjust escaping for your shell and operating system, and test the slate as a standalone file before adding it to a stream. Confirm the intended first number, update interval, and treatment of zero.
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The join has a gap, timestamp jump, or stream mismatch
With the concat demuxer, verify matching streams, codecs, and time bases, then inspect duration metadata for every input. If the media does not match or needs normalization, use the concat filter and re-encode instead. The formats documentation explains demuxer constraints; the FAQ distinguishes the available concat approaches.
Audio drops out during the slate
Check whether the slate has audio and whether its stream layout matches neighboring files. If uninterrupted audio is required, include silence or build continuous audio in the filtergraph, then map the intended output streams explicitly.
The output stops when the playlist ends
A finite render or playlist does not by itself define how a live process should behave after its last clip. Specify whether it should stop, repeat, wait for new material, or reconnect, and choose an approach that fits the output protocol. The relevant FFmpeg documentation covers filtergraphs and output options, but does not establish one universal persistent-live queue design.
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