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I'm trying to extract a subtitle from a Blu-ray disc and it is an hdmv_pgs_subtitle. So I try

ffmpeg -i file.m2ts -map 0:3 -scodec copy rip3/test.sub 

and get

Could not write header for output file #0 (incorrect codec parameters ?): 
Operation not permitted

Then I do

ffmpeg -i file.m2ts -map 0:3 -scodec copy rip3/test.sup 
ffmpeg -i file.m2ts -map 0:3 -scodec copy rip3/

and a bunch of other different extensions, until I give .mkv a shot, which works.

How can I find what extensions ffmpeg allows? I haven't found one place that e.g. names .mkv as an extension

ffmpeg -formats mentions matroska, but doesn't say that .mkv is the extension. So is there a way to find all supported file extensions for ffmpeg?

EDIT: After reading the answer from slhck I found the extensions by doing this command in the sourcefolder.

find . -type f -iname "*.c" -exec egrep -H ".extensions" {} \;

The filename will give some information about what kind of format it is.

share|improve this question
To my knowledge HDMV PGS subtitles cannot be "exported" to a standalone format. What do you need to do with the subtitles, specifically? – slhck Sep 23 '13 at 19:58
i've never been much good with ffmpeg but fwiw(prob not much!!)besides -formats there's also ffmpeg -codecs – barlop Sep 23 '13 at 19:58
@slhck it was for ripping a bluray I had. I wanted to dump audio and subtitles and encode the movie. This was really hard because I wanted to do it incrementally (first movie, audio and subtitles) and I couldn't manage to dump the subtitles because I couldn't find the proper extension. Read a couple of places that it was sup, and know of others that are sub, srt, mpsub and some others I saw doing ffmpeg -codecs and -formats. @ barlop fwiw codecs is what ffmpeg can read from and encode to not necessarily what it can output to. Format in the case of ffmpeg I think is the container of encoding. – plitter Sep 23 '13 at 20:40
up vote 3 down vote accepted

First off, you can see all formats (containers) by calling ffmpeg -formats. That they don't mention extensions is probably for the reason that an extension on its own is often meaningless, and you can override the output format by using the -f option.

You can see what the common extensions are for a particular (de)muxer. For example:

$ ffmpeg -v 1 -h demuxer=matroska
  Demuxer matroska,webm [Matroska / WebM]:
  Common extensions: mkv,mk3d,mka,mks

Output formats and their extensions are registered in the encoders. So, you'd find this for Matroska, when looking at the ffmpeg source code:

AVOutputFormat ff_matroska_muxer = {
    .name              = "matroska",
    .long_name         = NULL_IF_CONFIG_SMALL("Matroska"),
    .mime_type         = "video/x-matroska",
    .extensions        = "mkv",

Input formats are usually not parsed by their extension but the actual contained data.

Also see:

The problem is that only two of all the formats ffmpeg can handle support HDMV PGS subtitles:

  • MKV (Matroska)

You cannot use an SRT container because it's a different concept. SRT subtitles are based on text, while HDMV PGS subtitles are actual bitmaps.

So, this should work if all you need to do is store the subtitles somewhere:

ffmpeg -i input.mkv -c:s:0 copy -map 0:s:0 output.mkv
share|improve this answer
Thank you. Would you happen to know how I can find out what "things" you can put into what format? Is there a convenient list saying this format supports these "things"? – plitter Sep 23 '13 at 20:32
No, unfortunately it's not really that easy. One could, in theory, parse FFmpeg code in order to find out. Wikipedia has a fairly comprehensive list for common containers though. – slhck Sep 23 '13 at 20:50
Why not? The wiki looks good, but it seems outdated. Pgssub f.ex. isn't there it seems. – plitter Sep 23 '13 at 21:04

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