From 31311202dc855cbf6bf778b8039cd3d779789d11 Mon Sep 17 00:00:00 2001 From: Moritz Bunkus Date: Sat, 7 Feb 2015 20:37:49 +0100 Subject: [PATCH] Created Meta data fields like bitrate lost (markdown) --- Meta-data-fields-like-bitrate-lost.md | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) create mode 100644 Meta-data-fields-like-bitrate-lost.md diff --git a/Meta-data-fields-like-bitrate-lost.md b/Meta-data-fields-like-bitrate-lost.md new file mode 100644 index 0000000..6fb0136 --- /dev/null +++ b/Meta-data-fields-like-bitrate-lost.md @@ -0,0 +1,18 @@ +# Why are meta data fields like bitrate or encoder name lost when muxing to Matroska? + +## The problem + +You use tools like MediaInfo to show you information about source files and compare that with the information after you've muxed that file into a Matroska file. You notice that several pieces of information like e.g. the bitrate or the encoder name are not present in a Matroska file. + +## The answer + +The [Matroska file format](http://www.matroska.org/technical/specs/index.html) does not offer header fields for such pieces of information. In general only information that a codec might require for playback is stored in Matroska's track headers. Data that is simply informational can be stored in [Matroska tags](http://www.matroska.org/technical/specs/tagging/index.html) if you want, but mkvmerge does not do that automatically for you. + +You might notice that MediaInfo still shows bitrate information for some Matroska files but not for others. This may have two reasons: + +1. The bitrate might be stored on the bitstream level. This is only possible for audio/video types whose specifications provide fields for that kind of information in the bitstream. +2. If there's only a single track in a Matroska file then the bitrate can be estimated with the following formula: `bitrate_in_kbit_per_second = (file_size_in_bytes * 8) / (file_duration_in_seconds * 1024)` + +Note that starting with v7.0.0 mkvmerge [will create track-specific statistics](Automatic-tag-generation) and store them in tags. Newer versions of MediaInfo should be able to use that information properly. + +Categories: [merging](Category-merging), [metadata](Category-metadata)