I tried googling a way to set the language of a subtitle stream with ffmpeg and found the -slang option. So I tried the following command but immediately receive an error:
ffmpeg -i input.avi -i subs.srt -c:a copy -c:s mov_text -slang eng -c:v libx264 -profile:v high -level:v 4.0 output.mp4
ffmpeg version 1.1 Copyright (c) 2000-2013 the FFmpeg developers
built on Jul 18 2013 23:00:53 with Apple clang version 4.0 (tags/Apple/clang-421.0.60) (based on LLVM 3.1svn)
libavutil 52. 13.100 / 52. 13.100
libavcodec 54. 86.100 / 54. 86.100
libavformat 54. 59.106 / 54. 59.106
libavdevice 54. 3.102 / 54. 3.102
libavfilter 3. 32.100 / 3. 32.100
libswscale 2. 1.103 / 2. 1.103
libswresample 0. 17.102 / 0. 17.102
libpostproc 52. 2.100 / 52. 2.100
Unrecognized option 'slang'.
Error splitting the argument list: Option not found
After more googling I found another way to do it using the -metadata command:
ffmpeg -i input.mp4 -i subs.srt -c:a copy -c:v copy -c:s mov_text -metadata:s:s:0 language=eng output.mp4
And that works absolutely fine. But this isn't mentioned in the ffmpeg man page, whereas -slang is, which makes me think the -metadata command is maybe outdated or in some other way not as good as -slang.
- What is the difference between using the two above methods (-slang vs -metadata)?
- Why did my -slang command give an error? Have I used it incorrectly?
After some research, found the reason why -slang didn't work. In fact you use a recent version of ffmpeg and it's a good thing but if the documentation still describe the option, you can find in the ChangeLog:
version 0.9:
...
* -metadata can now be used to set metadata on streams and chapters, e.g.
-metadata:s:1 language=eng sets the language of the first stream to 'eng'.
This made -vlang/-alang/-slang options redundant, so they were removed.
When you find a command line example, check if the option used are in Your version of ffmpeg.
ffmpeg --help >> ffmpeg-doc.txt
The -slang
option isn't in.
But it also proof that the on-line documentation about ffmpeg is sometime incorrect regarding the code change.
The option
-metadata:s:1 language=eng
sets metadata language to eng
on the stream id 1 (which is, in typical cases, the first audio stream). Whereas the option
-metadata:s:s:0 language=eng
sets the metadata language to eng
on the first subtitle stream.
From ffmpeg manpage:
-metadata[:metadata_specifier] key=value (output,per-metadata)
Set a metadata key/value pair.
An optional metadata_specifier
may be given to set metadata on streams or chapters. See "-map_metadata" documentation for details.
s[:stream_spec]
per-stream metadata. stream_spec
is a stream specifier as described in the Stream specifiers chapter. In an input metadata specifier, the first matching stream is copied from. In an output metadata specifier, all matching streams are copied to.
And finally from the chapter of stream specifiers, we see
Possible forms of stream specifiers are:
stream_index
Matches the stream with this index. E.g. "-threads:1 4" would set the thread count for the second stream to 4.
stream_type[:stream_index]
stream_type
is one of: 'v' for video, 'a' for audio, 's' for subtitle, 'd' for data and 't' for attachments. If stream_index
is given, then matches stream number stream_index
of this type. Otherwise matches all streams of this type.