
Concatenate videos
The /video/concat Robot concatenates several videos together.
Warning: All videos you concatenate must have the same dimensions (width and height) and the same streams (audio and video streams) otherwise you will run into errors. If your videos do not have the desired dimensions when passing them to the /video/concat Robot, please encode them first with our /video/encode Robot.
It is possible to concatenate a virtually infinite number of video files using the /video/concat Robot.
Imagine you have three file input fields in the same upload form for video files that you want to concatenate. You can tell Transloadit in which order it should concatenate them using the file input field's name
attribute. Just use the value for the name attribute as the value for the fields
key in the JSON. Then set the proper order values in the as
parameter. Valid values here are video_[[index]]
. Transloadit will then concatenate them in the order of the index ascending:
"concatenated": {
"robot": "/video/concat",
"preset": "ipad-high",
"use": {
"steps": [
{ "name": ":original", "fields": "first_video_file", "as": "video_1" },
{ "name": ":original", "fields": "second_video_file", "as": "video_2" },
{ "name": ":original", "fields": "third_video_file", "as": "video_3" }
]
}
}
Parameters
-
use
String / Array of Strings / Object requiredSpecifies which Step(s) to use as input.
-
You can pick any names for Steps except
":original"
(reserved for user uploads handled by Transloadit) -
You can provide several Steps as input with arrays:
"use": [ ":original", "encoded", "resized" ]
That’s likely all you need to know about
use
, but you can view advanced use cases:› Advanced use cases
-
Step bundling. Some Robots can gather several Step results for a single invocation. For example, the /file/compress Robot would normally create one archive for each file passed to it. If you'd set
bundle_steps
to true, however, it will create one archive containing all the result files from all Steps you give it. To enable bundling, provide an object like the one below to theuse
parameter:"use": { "steps": [ ":original", "encoded", "resized" ], "bundle_steps": true }
This is also a crucial parameter for the /video/adaptive Robot, otherwise you'll generate 1 playlist for each viewing quality.
Keep in mind that all input Steps must be present in your Template. If one of them is missing (for instance it is rejected by a filter), no result is generated because the Robot waits indefinitely for all input Steps to be finished.Here’s a demo that showcases Step bundling.
-
Group by original. Sticking with the /file/compress Robot example, you can set
group_by_original
totrue
, in order to create a separate archive for each of your uploaded or imported files, instead of creating one archive containing all originals (or one per resulting file). This is important for for the /media/playlist Robot where you'd typically set:"use": { "steps": [ "segmented" ], "bundle_steps": true, "group_by_original": true }
-
Fields. You can be more discriminatory by only using files that match a field name by setting the
fields
property. When this array is specified, the corresponding Step will only be executed for files submitted through one of the given field names, which correspond with the strings in thename
attribute of the HTML file input field tag for instance. When using a back-end SDK, it corresponds withmyFieldName1
in e.g.:$transloadit->addFile('myFieldName1', './chameleon.jpg')
.This parameter is set to
true
by default, meaning all fields are accepted.Example:
"use": { "steps": [ ":original" ], "fields": [ "myFieldName1" ] }
-
Use as. Sometimes Robots take several inputs. For instance, the /video/merge Robot can create a slideshow from audio and images. You can map different Steps to the appropriate inputs.
Example:
"use": { "steps": [ { "name": "audio_encoded", "as": "audio" }, { "name": "images_resized", "as": "image" } ] }
Sometimes the ordering is important, for instance, with our concat Robots. In these cases, you can add an index that starts at 1. You can also optionally filter by the multipart field name. Like in this example, where all files are coming from the same source (end-user uploads), but with different
<input>
names:Example:
"use": { "steps": [ { "name": ":original", "fields": "myFirstVideo", "as": "video_1" }, { "name": ":original", "fields": "mySecondVideo", "as": "video_2" }, { "name": ":original", "fields": "myThirdVideo", "as": "video_3" } ] }
For times when it is not apparent where we should put the file, you can use Assembly Variables to be specific. For instance, you may want to pass a text file to the /image/resize Robot to burn the text in an image, but you are burning multiple texts, so where do we put the text file? We specify it via
${use.text_1}
, to indicate the first text file that was passed.Example:
"watermarked": { "robot": "/image/resize", "use" : { "steps": [ { "name": "resized", "as": "base" }, { "name": "transcribed", "as": "text" }, ], }, "text": [ { "text" : "Hi there", "valign": "top", "align" : "left", }, { "text" : "From the 'transcribed' Step: ${use.text_1}", "valign" : "bottom", "align" : "right", "x_offset": 16, "y_offset": -10, } ] }
-
-
preset
String ⋅ default:"flash"
Performs conversion using pre-configured settings.
If you specify your own FFmpeg parameters using the Robot's
ffmpeg
parameter and you have not specified a preset, then the default"flash"
preset is not applied. This is to prevent you from having to override each of the flash preset's values manually.For a list of video presets, see video presets.
-
video_fade_seconds
Float ⋅ default:1.0
When used this adds a video fade in and out effect between each section of your concatenated video. The float value is used so if you want a video delay effect of 500 milliseconds between each video section you would select
0.5
, however, integer values can also be represented.This parameter does not add a video fade effect at the beginning or end of your video. If you want to do so, create an additional /video/encode step and use our
ffmpeg
parameter as shown in this demo.Please note this parameter is independent of adding audio fades between sections.
-
audio_fade_seconds
Float ⋅ default:1.0
When used this adds an audio fade in and out effect between each section of your concatenated video. The float value is used so if you want an audio delay effect of 500 milliseconds between each video section you would select
0.5
, however, integer values can also be represented.This parameter does not add an audio fade effect at the beginning or end of your video. If you want to do so, create an additional /video/encode step and use our
ffmpeg
parameter as shown in this demo.Please note this parameter is independent of adding video fades between sections.
FFmpeg parameters
-
ffmpeg_stack
String ⋅ default:"v3.3.3"
Selects the FFmpeg stack version to use for encoding. These versions reflect real FFmpeg versions.
The current recommendation is to use
"v4.3.1"
. Other valid values can be found here. -
ffmpeg
Object ⋅ default:{}
A parameter object to be passed to FFmpeg. If a preset is used, the options specified are merged on top of the ones from the preset. For available options, see the FFmpeg documentation. Options specified here take precedence over the preset options.
Demos
- Concatenate video files
- Encode a fade effect between concatenated video files.
- Extract a preview from a video
- Insert an ad into a video at a specific time
- Join multiple videos sharing one audio track
Related blog posts
- Happy 2016 from Transloadit December 31, 2015
- Adding Four New Robots to Our Family! September 24, 2015
- Upgrading Encoding Engines July 31, 2015