How to keep chapters when converting WEBM to MP4

[johnr283]

I have a WEBM file with chapters. I converted it to MP4 using Avidemux but I lost the chapters. How can I convert it and keep the chapters?

[ProWo]

Step 1
ffmpeg -i your.webm -f ffmetadata FFMETADATAFILE.txt
Step 2
ffmpeg -i encoded.mp4 -i FFMETADATAFILE.txt -map_metadata 1 -codec copy encoded_with_chapters.mp4

[johnr283]

Step 1
ffmpeg -i your.webm -f ffmetadata FFMETADATAFILE.txt
Step 2
ffmpeg -i encoded.mp4 -i FFMETADATAFILE.txt -map_metadata 1 -codec copy encoded_with_chapters.mp4

Could you be more specific. How do I use ffmpeg?

[jagabo]

https://www.computerhope.com/issues/chusedos.htm
https://www.indeed.com/career-advice/career-development/how-to-run-program-in-command-prompt
https://www.wikihow.com/Run-a-Program-on-Command-Prompt

[johnr283]

I know how to use the command prompt. Do i create a file titled ffmpeg -i your.webm -f ffmetadata FFMETADATAFILE.txt then type ffmpeg -i encoded.mp4 -i FFMETADATAFILE.txt -map_metadata 1 -codec copy encoded_with_chapters.mp4 in the text file and run it from the command prompt? I tried this and got "'ffmpeg' is not recognized as an internal or external command, operable program or batch file."

[ProWo]

Step 1
ffmpeg -i your.webm -f ffmetadata FFMETADATAFILE.txt
Step 2
ffmpeg -i encoded.mp4 -i FFMETADATAFILE.txt -map_metadata 1 -codec copy encoded_with_chapters.mp4

Could you be more specific. How do I use ffmpeg?

Download this
https://www.videohelp.com/download/ffmpeg-5.1-full_build.7z
Extract it to any folder you like.
Put your files in the bin folder and open a command prompt in this bin folder.
Then copy the first commandline above at the commandprompt.
Change your.webm with your real filename and click enter.
Repeat with the second commandline.

[johnr283]

It says, "Output file is empty, nothing was encoded".

[ProWo]

Then use clever Ffmpeg-GUI.
Load your webm file, click main, click convert video stream, click keep size, click convert.
If done, click multiplex, select the green Videostream and the blue Audiostream, select mp4 as container and click multiplex.
Done.

[johnr283]

Then use clever Ffmpeg-GUI.
Load your webm file, click main, click convert video stream, click keep size, click convert.
If done, click multiplex, select the green Videostream and the blue Audiostream, select mp4 as container and click multiplex.
Done.

This worked. One more question though.
My original WEBM file is 682 MB. When I convert it to MP4 (HVEC x265) using Avidemux my resulting file is 512 MB.
When I use your method, clever Ffmpeg-GUI, WEBM to MP4 (HVEC x265) the resulting file is much smaller, 191 MB.

This seems like a big size difference to me. Why such a difference? Does it matter? I've checked both videos side by side and I don't see any noticeable in difference in quality.

[ProWo]

Use a lower CRF Value.
Lower means better quality and bigger file size.

[johnr283]

Use a lower CRF Value.
Lower means better quality and bigger file size.

Got it. Thanks again for all your help.

[johnr283]

Is there any good way to batch convert? I tried using FFmpeg Batch AV Converter with a CRF of 18 but the file size came out way to big, 8 gb.

[johnr283]

I'm using HandBrake it has batch encoding and it keep the chapters.