webm to mp4 conversion using ffmpeg

I was able to convert byffmpeg -i video.webm -strict experimental video.mp4.

As your input file report a strange frame rate value 1k fps coming from the tbs and tbr value (look here for their definition)

the encoder generate a different result, 16k tbn, 1k tbc (default)

So by calling :

ffmpeg -fflags +genpts -i 1.webm -r 24 1.mp4

You configure ffmpeg to generate new pts (a.k.a Presentation TimeStamp) for each frame and you set the target frame-rate to 24.

So your output mp4 file info (ffmpeg -i ....) change from

Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 4327 kb/s, 1000.09 fps, 1k tbr, 16k tbn, 2k tbc

to

Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1670 kb/s, 24 fps, 24 tbr, 12288 tbn, 48 tbc

Re-mux WebM to MP4

If you want to stream copy (re-mux) and avoid re-encoding:

ffmpeg -i input.webm -c copy output.mp4

This will copy the VP9/VP8 video and Opus/Vorbis audio from WebM to MP4. This is like a "copy and paste". No re-encoding occurs, so no quality is lost and the process is very fast.

(Note that if you were copying only the video and not the audio, you would use -c:v copy instead of -c copy. Point being, the -c part is the same meaning in both cases.)

If you get error: "opus in MP4 support is experimental"

If you get this error:

opus in MP4 support is experimental, add '-strict -2' if you want to use it.
Could not write header for output file #0 (incorrect codec parameters ?): Experimental feature

Then either:

• Use a newer ffmpeg as Opus in MP4 is no longer experimental in newer ffmpeg versions.
• Or add -strict experimental (or the alias -strict -2) if you are stuck with outdated ffmpeg.