ffmpeg - How to copy|extract encoding settings from existing media file?

Question

I wished to be able do this multiple times now so I ask.

If I have an existing video or audio file, ffmpeg, mplayer and other media players can detect at least some of it's "propreties" like container, codec and bitrate used, probably various quality and encoding specific settings, etc.

How can I extract these settings from an existing file in order to use them (directly) for encoding with ffmpeg?

For example, I got an mkv video encoded with x264 with some settings, and another uncompressed avi file. I would like to "copy" the encoding settings used in for x264 mkv file to transcode the avi with the same settings.

Note: I'm looking for a way that should include no human work with "translating" the settings from a decoder to the encoder. It is okay if I need to extract the settings first and save it somewhere but I would like to be able to simply feed the read options to a command line or preset|configuration file for ffmpeg.

Solution

There is no automatic way to do that. You have to look at the parameters of the original file and apply them to the output file.

In most cases, these will be the following:

• Container format (MP4, MKV, …)
• Video and audio codec (H.264, H.265, …)
• Audio-specific:
  • Number of audio channels
  • Audio sampling rate
  • Audio bitrate
• Video-specific:
  • Profile and Level (to ensure compatibility, see here)
  • Maximum bitrate limitations (e.g. for H.264)
  • Maximum video resolution, change via -filter:v scale or -s:v
  • Framerate, change via -filter:v fps -r
  • Chroma subsampling, change via -pix_fmt (e.g., -pix_fmt yuv420p should give you the best compatibility)
  • GOP size (distance between IDR-frames), set via -g
  • Other specific encoding settings

But even if you get that all right, some devices may require specific, proprietary information embedded in the bitstream.

---

As for the specific task of using x264, this is not going to be trivial. I'm not aware of a single script that'd take care of these tasks, which are usually done manually. For the most info about the encoding settings, on Unix/Linux or OS X, you can use mediainfo with some Bash tricks.

For example, for an x264-encoded video in an MP4 file:

mediainfo input.mp4 | grep "Encoding settings" | cut -d':' -f2- | tr '/' '\n' | sed 's/ //'

This will output a list of x264 options:

cabac=1
ref=3
deblock=1:-1:-1
analyse=0x3:0x113
me=hex
subme=7
psy=1
…

You could then manually pass these options to the x264 binary.

If you go through FFmpeg, that's a little more complicated though, as not all of x264's options can or should be mapped like this. Note that often a simple preset, tune and profile specification will do as well (as seen in x264 --fullhelp and the x264 encoding guide), and specifying the CRF level is enough.

And this is not even considering audio, where luckily, there aren't that many options.

Comments

[evilsoup]

Well, you could probably sort through the output of ffprobe (especially with the -show_streams and -show_format options) and use that information to script the important stuff

[Elisa Cha Cha]

Often using the same settings, such as bitrate (attempting to copy exact bitrate seems to be popular among users), will not result in optimal quality. Of course I have no clue what your typical input is like, but with x264 usage of the -crf option is generally recommended. See the FFmpeg and x264 Encoding Guide.

[thelolcat]

I can't find anything about encoding settings in ffprobe's output :(

[thelolcat]

It only shows the number of ReFrames, but not the other settings like mediainfo does

[jiggunjer]

Input syntax with ffmpeg is different from the metadata fields. e.g. you could read channels:6 from a video file, but to encode it you'd need to use the switch -ch:6. Some switches use 1 letter, some use two, etc.

[thelolcat]

So it's not possible with ffprobe or ffmpeg?

[slhck]

No, it's not directly possible to do it with ffprobe/ffmpeg. In case of x264-encoded video, I would use the mediainfo output and map these options to ffmpeg with -x264-params. (See also the x264 encoding guide). But if you want a general solution for all kinds of codecs/encoders or container formats, then you'd need to write a moderately sophisticated script that does the conversion.

[cduguet]

It's been 5 years now. Any new answer?

[slhck]

@cduguet This is as complicated today as it was five years ago, if not more, so no.

[1110101001]

Note that x264 includes the encoding settings in the bitstream. This is how mediainfo is able to show it (or you can use strings to see the same. ffprobe doesn't show it either, presumably because it only deals with generic properties for codecs/containers and not codec-specific metadata).