Vertically or horizontally stack (mosaic) several videos using ffmpeg?

Question

I have two videos of the same exact length, and I would like to use ffmpeg to stack them into one video file.

How can I do this?

Solution 1

See this answer to this question for a newer, simpler way to do this.

---

Old version:
You should be able to do this using the pad, movie and overlay filters in FFmpeg. The command will look something like this:

ffmpeg -i top.mov -vf 'pad=iw:2*ih [top]; movie=bottom.mov [bottom]; \
  [top][bottom] overlay=0:main_h/2' stacked.mov

First the movie that should be on top is padded to twice its height. Then the bottom movie is loaded. Then the bottom movie is overlaid on the padded top movie at an offset of half the padded movie's height.

Solution 2

Use the vstack (vertical), hstack (horizontal), or xstack (custom layout) filters. It is easier and faster than other methods.

Combine/stack two videos or images

Vertical

Using the vstack filter.

ffmpeg -i input0 -i input1 -filter_complex vstack=inputs=2 output

Videos must have the same width.

Horizontal

Using the hstack filter.

ffmpeg -i input0 -i input1 -filter_complex hstack=inputs=2 output

Videos must have the same height.

With a border

Using the pad filter. This examples creates a 5px black border between the two sides.

ffmpeg -i input0 -i input1 -filter_complex "[0]pad=iw+5:color=black[left];[left][1]hstack=inputs=2" output

---

With audio

Downmix and use original channel placements

Add the amerge filter to combine the audio channels from both inputs:

ffmpeg -i input0 -i input1 -filter_complex "[0:v][1:v]vstack=inputs=2[v];[0:a][1:a]amerge=inputs=2[a]" -map "[v]" -map "[a]" -ac 2 output

• This assumes each input contains a stereo audio stream.

• -ac 2 is included to downmix to stereo in case both inputs contain multi-channel audio. For example, if both inputs are stereo, you would get a 4-channel output audio stream instead of stereo if you omit -ac 2.

Put all audio from each input into separate channels

Use amerge (or amix) and pan filters:

ffmpeg -i input0 -i input1 -filter_complex "[0:v][1:v]vstack=inputs=2[v];[0:a][1:a]amerge=inputs=2,pan=stereo|c0<c0+c1|c1<c2+c3[a]" -map "[v]" -map "[a]"  output

• This assumes each input contains a stereo audio stream.

Using audio from one particular input

This example will use the audio from input1:

ffmpeg -i input0 -i input1 -filter_complex "[0:v][1:v]vstack=inputs=2[v]" -map "[v]" -map 1:a output

Adding silent audio / If one input does not have audio

If you mix inputs that have audio and inputs that do not have audio then amerge will fail because each input needs audio. You can add silent audio with the anullsrc filter to prevent this:

ffmpeg -i input0 -i input1 -filter_complex "[0:v][1:v]vstack=inputs=2[v];anullsrc[silent];[0:a][silent]amerge=inputs=2[a]" -map "[v]" -map "[a]" -ac 2 output.mp4

---

3 videos or images

ffmpeg -i input0 -i input1 -i input2 -filter_complex "[0:v][1:v][2:v]hstack=inputs=3[v]" -map "[v]" output

If you want vertical use vstack instead of hstack.

---

2x2 grid

Using xstack

ffmpeg -i input0 -i input1 -i input2 -i input3 -filter_complex "[0:v][1:v][2:v][3:v]xstack=inputs=4:layout=0_0|w0_0|0_h0|w0_h0[v]" -map "[v]" output

Using hstack and vstack

ffmpeg -i input0 -i input1 -i input2 -i input3 -filter_complex "[0:v][1:v]hstack=inputs=2[top];[2:v][3:v]hstack=inputs=2[bottom];[top][bottom]vstack=inputs=2[v]" -map "[v]" output

This syntax is easier to understand, but less efficient than using xstack as shown above.

---

2x2 grid with text

Using the drawtext filter:

ffmpeg -i input0 -i input1 -i input2 -i input3 -filter_complex
"[0]drawtext=text='vid0':fontsize=20:x=(w-text_w)/2:y=(h-text_h)/2[v0];
 [1]drawtext=text='vid1':fontsize=20:x=(w-text_w)/2:y=(h-text_h)/2[v1];
 [2]drawtext=text='vid2':fontsize=20:x=(w-text_w)/2:y=(h-text_h)/2[v2];
 [3]drawtext=text='vid3':fontsize=20:x=(w-text_w)/2:y=(h-text_h)/2[v3];
 [v0][v1][v2][v3]xstack=inputs=4:layout=0_0|w0_0|0_h0|w0_h0[v]"
-map "[v]" output

---

4x4

Use the xstack filter. Example for a total of 16 videos:

ffmpeg -i input0 -i input1 -i input2 -i input3 -i input4 -i input5 -i input6 -i input7 -i input8 -i input9 -i input10 -i input11 -i input12 -i input13 -i input14 -i input15 -i input16 -filter_complex "[0:v][1:v][2:v][3:v][4:v][5:v][6:v][7:v][8:v][9:v][10:v][11:v][12:v][13:v][14:v][15:v]xstack=inputs=16:layout=0_0|w0_0|w0+w1_0|w0+w1+w2_0|0_h0|w4_h0|w4+w5_h0|w4+w5+w6_h0|0_h0+h4|w8_h0+h4|w8+w9_h0+h4|w8+w9+w10_h0+h4|0_h0+h4+h8|w12_h0+h4+h8|w12+w13_h0+h4+h8|w12+w13+w14_h0+h4+h8" output.mp4

If you need to scale the inputs first:

ffmpeg -i input0 -i input1 -i input2 -i input3 -i input4 -i input5 -i input6 -i input7 -i input8 -i input9 -i input10 -i input11 -i input12 -i input13 -i input14 -i input15 -i input16 -filter_complex "[0:v]scale=iw/4:-1[v0];[1:v]scale=iw/4:-1[v1];[2:v]scale=iw/4:-1[v2];[3:v]scale=iw/4:-1[v3];[4:v]scale=iw/4:-1[v4];[5:v]scale=iw/4:-1[v5];[6:v]scale=iw/4:-1[v6];[7:v]scale=iw/4:-1[v7];[8:v]scale=iw/4:-1[v8];[9:v]scale=iw/4:-1[v9];[10:v]scale=iw/4:-1[v10];[11:v]scale=iw/4:-1[v11];[12:v]scale=iw/4:-1[v12];[13:v]scale=iw/4:-1[v13];[14:v]scale=iw/4:-1[v14];[15:v]scale=iw/4:-1[v15];[v0][v1][v2][v3][v4][v5][v6][v7][v8][v9][v10][v11][v12][v13][v14][v15]xstack=inputs=16:layout=0_0|w0_0|w0+w1_0|w0+w1+w2_0|0_h0|w4_h0|w4+w5_h0|w4+w5+w6_h0|0_h0+h4|w8_h0+h4|w8+w9_h0+h4|w8+w9+w10_h0+h4|0_h0+h4+h8|w12_h0+h4+h8|w12+w13_h0+h4+h8|w12+w13+w14_h0+h4+h8" output.mp4

---

Resize/scale an input

Since both videos need to have the same with for vstack, and the same height for hstack, you may need to scale one of the other videos to match the other:

Simple scale filter example to set width of input0 to 640 and automatically set height while preserving the aspect ratio:

ffmpeg -i input0 -i input2 -filter_complex "[0:v]scale=640:-1[v0];[v0][1:v]vstack=inputs=2" output

• For a more advanced method to fit any size video into a specific size while preserving aspect ratio see Resizing videos with ffmpeg to fit into static sized player.

• You can also use the scale2ref filter to automatically resize one video to match the dimensions of the other.

---

Delaying/pausing videos

This example will play the top left video while pausing the others. Once the top left video ends the top right video will play and so on.

Use the tpad, adelay, xstack, and amix filters:

ffmpeg -i top-left.mp4 -i top-right.mp4 -i bottom-left.mp4 -i bottom-right.mp4 -filter_complex "[1]tpad=start_mode=clone:start_duration=5[tr];[2]tpad=start_mode=clone:start_duration=10[bl];[3]tpad=start_mode=clone:start_duration=15[br];[0][tr][bl][br]xstack=inputs=4:layout=0_0|w0_0|0_h0|w0_h0[v];[1:a]adelay=5s:all=true[a1];[2:a]adelay=10s:all=true[a2];[3:a]adelay=15s:all=true[a3];[0:a][a1][a2][a3]amix=inputs=4[a]" -map "[v]" -map "[a]" output.mp4

• This example assumes each input is 5 seconds duration. Adjust start_duration and adelay values as needed.

• This command requires FFmpeg 4.3 or newer.

• If you don't like the complexity of xstack you can use several hstack/vstack instead as shown in Example 4: 2x2 grid.

Comments

[frans]

ffmpeg reports No such filter: 'vstack'. Do I have to install it first?

[llogan]

@frans You probably figured this out by now, but your ffmpeg is too old. Users are recommended to use a ffmpeg build derived from the current git master branch.

[RaduM]

Stream specifier ':a' in filtergraph description [0:v][1:v]vstack[v];[0:a][1:a]amerge=inputs=2[a] matches no streams. Why do I get this?

[Jeffin]

@RaduM its because one of your video doesnt have audio in it , you need to add an audio or silent audio in it , try the same command using two videos with Audio , it will work , am posting because I had the same problem today and rectified it using silent audio addition.

[Nasseh]

@LordNeckbeard I used your Example 2 command for merging two videos. It did worked for me and I got an output with two videos merged along with their Audios mixed. What is the command if I add a third file, say an mp3 file, and merge 2 videos as before and merge 3 audios together.

[llogan]

@Nasseh ffmpeg -i input0 -i input1 -i input2 -filter_complex "[0:v][1:v]vstack[v];[0:a][1:a][2:a]amerge=inputs=3[a]" -map "[v]" -map "[a]" -ac 2 -shortest output

[Nasseh]

Thanks @LordNeckbeard. It worked fine. Well done! It works very well for two videos which are the same. What any other option is needed to be added to the above command for two videos which are not the same. I say this because I tried to merge two videos which are different in size, scale, resolution, ... and got errors like these: "No Channel Layout for input1", Input Channel Layouts overlap...", "Failed to inject frame into filter network", "Error while processing the decoded data for stream".

[llogan]

@Nasseh You'll need to use more filters, such as scale, crop and/or pad, to make each video the same before stacking them.

[Admin]

@LordNeckbeard Just curious, since I am not very familiar with audio processing, what is the implication of 4-channel output audio? Why should I downmix to stereo?

[llogan]

@user2675516 Not all encoders or formats support 4.0 (for example flac, opus, vorbis). According to ffmpeg -layouts 4.0 maps as FL+FR+FC+BC which is Front Left, Front Right, Front Center, and Back Center. If the merged audio is suitable for this layout, and your format or encoder supports this, then you can keep it as 4.0.

[Admin]

@LordNeckbeard if it is not supported, it means the audio wont play?

[llogan]

@user2675516 ffmpeg will tell you if it is supported or not: you may get an error message such as 4.0 not supported by Vorbis: output stream will have incorrect channel layout. Some encoders will provide such a message and still output a file, and others will just give an error and not provide an output file.

[Kong]

your 3 video example stacks vertically. how do i stack them horizontally

[Kong]

and how do i stack 2 rows 3 columns ?

[Kong]

ffmpeg -i front.avi -i front.avi -i front.avi -i front.avi -i front.avi -i front.avi -filter_complex "[0:v][1:v][2:v]hstack=3[top];[3:v][4:v][5:v]hstack=3[bottom‌​];[top][bottom]vstac‌​k[v]" -map "[v]" output.avi ............... but i cannot open the avi file

[llogan]

@UpvotesAllDownvotedPosts Not enough info. Need to see the complete log.

[Kong]

its too long to be posted here so i created a thread for it. stackoverflow.com/questions/52770397/… i hope you can take a look

[Classsic]

Is there a way to get sync of multiple live inputs? I see some setpts=PTS-STARTPTS filters parameter, but doesn´t work for live inputs. Any clue?

[llogan]

@Classsic Is the sync issue a constant delay (always n seconds off) or does the sync delay change over time?

[Classsic]

Change every time, the command start, is not fixed, I can see the delay is the same of GOP size, but the 1st stream acumulate the delay of GOP size of 2nd+3th+4th.

[llogan]

@Classsic Should be asked as a new question at Super User. Show your command and the complete log.

[jetblack]

What if the inputs have different length? Assuming one knows the timestamps, how can they be aligned?

[llogan]

@jetblack If they have different lengths then the shorter video will stop while the longer one continues unless you use the shortest=1 option. To align you can use filters such as adelay and tpad and/or -ss and -t options.

[Zain Ali]

@llogan Can you tell that how ffmpeg assign SAR/DAR to stacked output videos, the above method works but it sometime create videos with strange SAR/DAR that does not play on most players, e.g., video with resolution 2272x1280 & SAR/DAR 61:194/4331:7760

[llogan]

@ZainAli Can you use Firefox Send or a pastebin site to show your full command and the complete log? Then provide a link in a comment.