{ "schemaVersion": 1, "contentVersion": "ca42e61ede0a24f789d7287a0001244ad22f4abf", "id": "docs/guides/audio-and-subtitles", "collection": "docs", "title": "Audio and subtitles", "description": "Keep, re-encode, label and synchronize audio and subtitle tracks with FFmpeg, convert subtitles for MP4, and burn subtitles into the picture.", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/", "apiUrl": "https://encode.wiki/api/v1/documents/docs/guides/audio-and-subtitles.json", "markdownUrl": "https://encode.wiki/api/v1/markdown/docs/guides/audio-and-subtitles.md", "status": "current", "tags": [ "audio", "subtitles", "ffmpeg" ], "license": "CC BY-SA 4.0", "dates": { "lastVerified": "2026-10-08T00:00:00.000Z" }, "authors": [], "sources": [ { "title": "FFmpeg documentation — stream specifiers, mapping, metadata and dispositions", "url": "https://ffmpeg.org/ffmpeg.html", "accessedAt": "2026-10-08T00:00:00.000Z" }, { "title": "FFmpeg filters — subtitles and overlay", "url": "https://ffmpeg.org/ffmpeg-filters.html#subtitles-1", "accessedAt": "2026-10-08T00:00:00.000Z" }, { "title": "Matroska — subtitle mappings", "url": "https://www.matroska.org/technical/subtitles.html", "accessedAt": "2026-10-08T00:00:00.000Z" }, { "title": "libass — ASS file format guide (fonts)", "url": "https://github.com/libass/libass/wiki/ASS-File-Format-Guide", "accessedAt": "2026-10-08T00:00:00.000Z" }, { "title": "MKVToolNix — mkvmerge documentation", "url": "https://mkvtoolnix.download/doc/mkvmerge.html", "accessedAt": "2026-10-08T00:00:00.000Z" }, { "title": "Xiph.org — Opus recommended settings", "url": "https://wiki.xiph.org/Opus_Recommended_Settings", "accessedAt": "2026-10-08T00:00:00.000Z" }, { "title": "FFmpeg libopusenc.c at n9.0.2 (layout check and mapping families)", "url": "https://github.com/FFmpeg/FFmpeg/blob/n9.0.2/libavcodec/libopusenc.c", "accessedAt": "2026-10-08T00:00:00.000Z" } ], "headings": [ { "depth": 2, "text": "Stream numbering", "anchor": "stream-numbering" }, { "depth": 2, "text": "Keep everything and change nothing", "anchor": "keep-everything-and-change-nothing" }, { "depth": 2, "text": "Re-encode audio, copy the rest", "anchor": "re-encode-audio-copy-the-rest" }, { "depth": 2, "text": "Set languages, titles and default tracks", "anchor": "set-languages-titles-and-default-tracks" }, { "depth": 2, "text": "Subtitles in MP4 and on the web", "anchor": "subtitles-in-mp4-and-on-the-web" }, { "depth": 2, "text": "Fonts for ASS subtitles", "anchor": "fonts-for-ass-subtitles" }, { "depth": 2, "text": "Burn subtitles into the picture", "anchor": "burn-subtitles-into-the-picture" }, { "depth": 2, "text": "Fix audio that is out of sync", "anchor": "fix-audio-that-is-out-of-sync" } ], "sections": [ { "id": "_preamble", "title": "Page introduction", "depth": 0, "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/_preamble.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/_preamble.md", "checksum": "151ef1fcd6055670a66df4d3f09255b6f6c7fb4ff766deafafffdccc36e44237", "bytes": 319 }, { "id": "stream-numbering", "title": "Stream numbering", "depth": 2, "anchor": "stream-numbering", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#stream-numbering", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/stream-numbering.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/stream-numbering.md", "checksum": "a9fccbe1e6d8ce3fadc9f45c1e08e1bc612fdded586a45a452cf88bf289ed95e", "bytes": 610 }, { "id": "keep-everything-and-change-nothing", "title": "Keep everything and change nothing", "depth": 2, "anchor": "keep-everything-and-change-nothing", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#keep-everything-and-change-nothing", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/keep-everything-and-change-nothing.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/keep-everything-and-change-nothing.md", "checksum": "df9ad55d07174dc5dc5c164e288df66311c195a8c92cf514629ad063ad4982fe", "bytes": 774 }, { "id": "re-encode-audio-copy-the-rest", "title": "Re-encode audio, copy the rest", "depth": 2, "anchor": "re-encode-audio-copy-the-rest", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#re-encode-audio-copy-the-rest", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/re-encode-audio-copy-the-rest.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/re-encode-audio-copy-the-rest.md", "checksum": "3fb2cd41c03318d77cd55a2fb1dcd14d221a00262103565e1696c3b5928ce598", "bytes": 1257 }, { "id": "set-languages-titles-and-default-tracks", "title": "Set languages, titles and default tracks", "depth": 2, "anchor": "set-languages-titles-and-default-tracks", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#set-languages-titles-and-default-tracks", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/set-languages-titles-and-default-tracks.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/set-languages-titles-and-default-tracks.md", "checksum": "6f59c7c295c11ab8b8a6f5a237cf7b58bffeb144f64073525e3e4fe073abdc86", "bytes": 809 }, { "id": "subtitles-in-mp4-and-on-the-web", "title": "Subtitles in MP4 and on the web", "depth": 2, "anchor": "subtitles-in-mp4-and-on-the-web", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#subtitles-in-mp4-and-on-the-web", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/subtitles-in-mp4-and-on-the-web.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/subtitles-in-mp4-and-on-the-web.md", "checksum": "c43092ff3ed6b4b0695a22989fd478ff33ef4b3976987b16f7a9669ead23463b", "bytes": 1697 }, { "id": "fonts-for-ass-subtitles", "title": "Fonts for ASS subtitles", "depth": 2, "anchor": "fonts-for-ass-subtitles", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#fonts-for-ass-subtitles", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/fonts-for-ass-subtitles.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/fonts-for-ass-subtitles.md", "checksum": "5854ebaa29eab141cc9db2bce3a66e0c9377ecdb16c171135934f883d2f5a45d", "bytes": 397 }, { "id": "burn-subtitles-into-the-picture", "title": "Burn subtitles into the picture", "depth": 2, "anchor": "burn-subtitles-into-the-picture", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#burn-subtitles-into-the-picture", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/burn-subtitles-into-the-picture.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/burn-subtitles-into-the-picture.md", "checksum": "b684870e08098786b96eb6852e2dea9f5a98fd61e600d8a4bce9721a50b6e3ef", "bytes": 1071 }, { "id": "fix-audio-that-is-out-of-sync", "title": "Fix audio that is out of sync", "depth": 2, "anchor": "fix-audio-that-is-out-of-sync", "canonicalUrl": "https://encode.wiki/guides/audio-and-subtitles/#fix-audio-that-is-out-of-sync", "apiUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/fix-audio-that-is-out-of-sync.json", "markdownUrl": "https://encode.wiki/api/v1/sections/docs/guides/audio-and-subtitles/fix-audio-that-is-out-of-sync.md", "checksum": "3ddff032faab88286affbc5e4e32d56a2b8d773d79b7400354c3d79073334ce7", "bytes": 791 } ], "outboundReferences": [ "/codecs/subtitles/srt/", "/codecs/subtitles/ssa/", "/codecs/subtitles/webvtt/", "/tools/utilities/mkvtoolnix/" ], "checksum": "41a5ccc8d423e61cdb8edd94121c9b75b45bf17c84ab334c687ddeb9841f42b7", "contentFormat": "markdown", "markdown": "A film or episode usually carries more than one video and one audio stream: several languages,\ncommentary, full and forced subtitles, chapters and attached fonts. This guide covers keeping the\nones you want, re-encoding audio, labelling tracks, getting subtitles into MP4, burning subtitles in,\nand fixing audio delay.\n\n## Stream numbering\n\nRun `ffprobe -hide_banner input.mkv` to list the streams. FFmpeg's stream specifiers count in two\nways:\n\n- `0:3` is stream 3 of input 0, counting all streams.\n- `0:a:1` is the second **audio** stream of input 0, counting only that type from zero.\n\nOptions that act on output streams, such as `-c:a:1` or `-metadata:s:a:1`, use the numbering of the\n**output** file. If you map the source's second audio track first, it becomes output `a:0`.\n\nOnce you use `-map`, FFmpeg writes only the streams you list. Without it, it keeps one video, one\naudio and one subtitle stream and drops the rest.\n\n## Keep everything and change nothing\n\n```sh\nffmpeg -i input.mkv -map 0 -c copy output.mkv\n```\n\n`-map 0` takes every stream, including attachments such as fonts; `-c copy` copies them without\nre-encoding. Chapters and global metadata are copied by default. This is how you change container\nor drop tracks without any quality loss. For detailed Matroska editing (track order, flags, header\nedits without remuxing) [MKVToolNix](/tools/utilities/mkvtoolnix/) is often more convenient.\n\nTo drop tracks, map selectively. This keeps the video, the first audio track and every subtitle\nstream (`?` makes the subtitle map optional; the quotes stop zsh from treating `?` as a wildcard):\n\n```sh\nffmpeg -i input.mkv -map 0:v:0 -map 0:a:0 -map '0:s?' -map '0:t?' -c copy output.mkv\n```\n\n## Re-encode audio, copy the rest\n\n```sh\nffmpeg -i input.mkv -map 0 -c copy -c:a libopus -b:a:0 128k -b:a:1 256k output.mkv\n```\n\n`-c copy` applies to everything and `-c:a libopus` then overrides it for audio. Set bitrates per\noutput stream: about 128 kbit/s for stereo and 256 kbit/s for 5.1 are good Opus starting points.\n\nlibopus rejects the common `5.1(side)` layout with `Invalid channel layout 5.1(side) for specified\nmapping family`, and `-mapping_family 1` on its own does not change that. Convert the surround\ntrack to plain 5.1 with a filter that targets only that output stream:\n\n```sh\nffmpeg -i input.mkv -map 0 -c copy -c:a libopus -b:a:0 128k -b:a:1 256k \\\n -filter:a:1 aformat=channel_layouts=5.1 -mapping_family:a:1 1 output.mkv\n```\n\n`aformat` moves the side channels to the back positions without downmixing. A bare `-af` would\napply to every audio stream and upmix the stereo track to 5.1 as well. `-mapping_family 1` switches\nlibopus to its surround encoder, which uses masking between channels to spend the bits better.\n\nCopy audio that already plays on your targets. Re-encoding a lossy track (AC-3, DTS, AAC) adds\nanother generation of loss; re-encoding lossless tracks (FLAC, PCM, TrueHD, DTS-HD MA) to Opus saves\nmost of their size.\n\n## Set languages, titles and default tracks\n\n```sh\nffmpeg -i input.mkv -map 0:v:0 -map 0:a:0 -map 0:a:1 -map 0:s:0 -c copy \\\n -metadata:s:a:0 language=eng -metadata:s:a:0 title=\"Stereo\" \\\n -metadata:s:a:1 language=jpn \\\n -disposition:a:0 default -disposition:a:1 0 -disposition:s:0 0 \\\n output.mkv\n```\n\nLanguages are ISO 639-2 codes (`eng`, `jpn`, `ger`…). A disposition value replaces all of that\nstream's flags, so `0` clears them. Players use the `default` flag when the viewer has no language\npreference; they may ignore it when one is set.\n\nA **forced** subtitle track holds only what should appear when full subtitles are off, such as\ntranslated signs and foreign-language lines. Mark such a track with `-disposition:s:0 forced`. The\nflag does not extract forced lines from a full subtitle track.\n\n## Subtitles in MP4 and on the web\n\n| Target | Subtitle format | Notes |\n| -------------------------------- | ---------------------------------------------------------------------------------------- | --------------------------------------------------------------------------- |\n| MKV | Copy anything: [SRT](/codecs/subtitles/srt/), [ASS](/codecs/subtitles/ssa/), PGS, VobSub | Keep ASS fonts as attachments. |\n| MP4 | `mov_text` (converted from SRT or ASS) | ASS styling and positioning are lost. Bitmap subtitles cannot be converted. |\n| HTML `