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To start separate FFmpeg outputs at different positions in their source videos, put a seek option such as -ss before each input’s -i. For example, seek one input to 2:00 and another to 5:00. Use -itsoffset instead only when you need to shift timestamps; it does not select a different scene or song.
The distinction matters: FFmpeg options are order-sensitive and generally apply to the next input or output. The examples below show how to scope seeks and mappings, but they do not establish that YouTube will accept multiple distinct broadcasts from one FFmpeg process and one stream key.
Choose the right kind of “start time”
“Playlist start time” can refer to several different things. Identify the desired result before changing FFmpeg options:
| What you want | Use | What it changes |
|---|---|---|
| Begin each source at a different scene, song, or media position | -ss before that source’s -i |
The position read from that input |
| Delay or shift a stream’s timestamps | -itsoffset before that input’s -i |
Input timestamps; a positive offset delays the corresponding streams |
| Begin reading an incoming live HLS playlist at a different segment | The HLS demuxer’s live_start_index |
The segment index used when reading the live playlist |
| Start an actual broadcast at a scheduled wall-clock time | Configure the broadcast schedule in the relevant platform workflow | When the broadcast begins, not the source media position |
FFmpeg’s -ss documentation describes seeking to a position in the input; its documented output-side form instead decodes and discards content until the requested position. See FFmpeg command-line documentation. The input timestamp option -itsoffset adds an offset to input timestamps, with a positive value delaying the streams: FFmpeg advanced options.
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Set a different source position for each output
Place each -ss immediately before the corresponding -i. Then map that input’s streams to its intended output. This schematic example seeks the first file to 2:00 and the second to 5:00:
ffmpeg
-ss 00:02:00 -i inputA.mp4
-map 0:v? -map 0:a? -c:v libx264 -c:a aac OUTPUT_A
-ss 00:05:00 -i inputB.mp4
-map 1:v? -map 1:a? -c:v libx264 -c:a aac OUTPUT_BReplace the input paths, output destinations, and codec settings for your workflow. This illustrates per-input seeks and mappings; it is not a tested YouTube ingest command. Choose an output format and transport compatible with the ingest protocol you use.
Why option order matters
-ss 00:02:00 -i inputA.mp4seeksinputA.mp4.-ss 00:05:00 -i inputB.mp4seeksinputB.mp4; it does not retroactively change the first input.- Options are scoped by their position in the command and generally apply to the next input or output. Options reset between files, so specify the relevant settings again for each file.
Map each input deliberately
In the example, -map 0:v? and -map 0:a? select optional video and audio streams from the first input; -map 1:v? and -map 1:a? do the same for the second. The question mark makes a mapping optional, which can help when a source lacks one of those stream types. Verify the input numbering and stream layout for your actual files before sending the outputs anywhere.
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Use -itsoffset for timestamp alignment, not a different playlist position
-itsoffset is an input option that adds a specified offset to input timestamps. For example, a positive offset delays the corresponding streams. It does not tell FFmpeg to begin at a later song, scene, or playlist item. Use -ss for a different media position; use -itsoffset when timestamps need to be shifted.
Because both are input options, place the chosen option before the matching -i. Consult the FFmpeg advanced options documentation for the option syntax and semantics.
Do not confuse HLS variants with independent starts
Multiple HLS variant playlists are normally renditions of one presentation—such as different quality versions—not instructions to begin separate broadcasts at different source positions. FFmpeg configures variant outputs with stream mappings and var_stream_map. When generating two or more variants, its HLS documentation requires %v in the output filename pattern. See FFmpeg HLS format documentation.
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If you need separate outputs that begin at different points in separate source files, configure the inputs and output mappings individually, as in the earlier example. A variant setup alone does not create independent content-start schedules.
For an incoming live HLS playlist, select a segment
If the source is a live HLS playlist rather than a local recording, FFmpeg’s HLS demuxer provides the live_start_index option. It selects the segment index from which to start; negative indices count from the end of the playlist. The demuxer also documents prefer_x_start, which can prefer an #EXT-X-START tag in the playlist. These are input-reading behaviors, not wall-clock scheduling controls. See the FFmpeg HLS format documentation.
Check YouTube’s HLS ingest requirements
If you send the output using HLS ingest, the timing options do not replace YouTube’s transport and segment requirements. YouTube’s HLS setup documentation specifies:
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- Transport stream (TS) segments lasting 1–4 seconds.
- A rolling playlist with no more than five outstanding segments.
- HTTPS POST or PUT; byte ranges are not supported.
- HLS has higher latency because video is sent in segments; YouTube’s Ultra low-latency option is turned off for HLS.
These requirements apply to HLS ingestion. Confirm the current ingest settings in YouTube Live Control Room. See YouTube’s HLS ingestion setup guide and YouTube live encoder settings and bitrates.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot the most common timing mistakes
Both outputs begin at the same source position
Check that each -ss appears before its own -i. An output-side seek or a seek placed before the wrong input will not express two independent input positions.
The wrong video or audio appears in an output
Review the input indexes in each -map. FFmpeg numbers inputs in command order, beginning with 0; the second input in the example is 1. Confirm that the mapped streams exist in that file.
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The stream is delayed, but begins at the wrong scene
That is consistent with a timestamp shift rather than a media seek. Replace the timestamp adjustment with -ss before the relevant input if you need a different source position.
The HLS variants do not start independently
Variant playlists represent renditions of a presentation, not separate start schedules. Configure independent sources and outputs if they must begin at distinct positions.
YouTube rejects the HLS output or latency is higher than expected
Check the segment duration, rolling playlist, HTTPS method, and byte-range behavior against YouTube’s HLS requirements, then verify the current settings in Live Control Room. HLS’s segmented delivery has higher latency, and YouTube’s Ultra low-latency option is disabled for HLS.
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