HEVC to M4B Converter

Turning an H.265 Recording into an Audiobook File: What This Covers

M4B is not a different codec from M4A — it is the same MPEG-4 Part 14 file (ISO/IEC 14496-14:2003) with an AAC track inside, carrying a different extension. That extension is a behavioural signal: Apple Books, Apple Podcasts and most dedicated audiobook players read .m4b as spoken-word material and remember where you stopped between sessions, while a .m4a is filed as music and restarts from the top. This walk-through covers pulling the audio out of an H.265 recording into that form, choosing a bitrate that suits a voice rather than a band, and the two limits worth knowing before you start: the source has to contain an audio track in the first place, and this conversion does not write chapter markers.

How to Convert HEVC to M4B

1. Upload Your HEVC File: Drag your .hevc onto the page or click "+ Add Files" to browse. Several recordings can be queued and converted with the same settings in one pass.
2. Choose a File Compression Mode: There is no codec to choose here — an M4B carries AAC and that is what this page writes. Under File Compression, Constant Bitrate is the mode to use when the number matters: the dropdown runs 8 kbps to 384 kbps and opens on 128 kbps. Custom Bitrate takes a typed value and is prefilled at 128 Kbps; Specific file size takes a target in megabytes, prefilled at 8.
3. Set Audio Channel, Audio Sample Rate or Trim: Audio Channel offers Original, Mono and Stereo — Mono is the right answer for a single narrator. Audio Sample Rate offers Original, 8000, 12000, 16000, 24000, 44100 and 48000 Hz. Trim → Time Range takes a Start time and a Duration in seconds or HH:MM:SS.sss, which is how you cut a title card or dead air off the front.
4. Convert and Download: Click "Convert" and save the .m4b. Your file is uploaded over an encrypted connection, converted on our servers, and deleted automatically a few hours later. No sign-up, no watermark.

Walk-through: Picking a Bitrate for Spoken Word

The bitrate rung that suits music is roughly double what a voice needs, and the difference compounds badly over an audiobook's length. Speech occupies a narrow band, has long near-silent gaps, and is often effectively mono even when it was recorded in stereo — all things AAC handles very efficiently once you stop asking it to preserve a stereo image that carries no information.

• Set Constant Bitrate rather than leaving it on Quality Preset. Quality Preset is the mode the page opens on, but it is the automatic, hands-off option and the least predictable control here — and nothing is pre-selected in its dropdown, so leaving it alone means the server falls back to its own default rather than the "Highest" shown on screen. Constant Bitrate gives you a number you chose and a size you can work out in advance.
• Fold a single narrator to Mono. Setting Audio Channel to Mono roughly halves the data the encoder has to describe when the two channels are near-identical, which they are on almost any lecture, sermon, interview or voice memo.
• Drop the sample rate only if the recording is already narrowband. 24000 Hz is plenty for a voice and shaves a little more off; leave it on Original if the source has music beds, applause or anything else with high-frequency content.
• Do the arithmetic before you commit. File size for a constant bitrate is simply rate times duration: 64,000 bits per second over 3,600 seconds is 28.8 MB per hour. We used exactly that calculation for the table below rather than measuring anything, so the figures scale directly with the length of your recording.

Bitrate Guide for a Spoken-Word M4B

M4A and M4B — the Same Bytes, Different Behaviour

Common Errors and How to Fix Them

• "The M4B is silent" — The source had no audio track. A genuine .hevc file is an Annex B elementary stream and HEVC covers picture only, so a raw stream from a screen recorder or DVR has no sound to extract. Go back to the .mp4, .mov or .mkv the video was demuxed from.
• "There are no chapters" — Expected. The M4B container supports chapter markers, but this conversion writes a single continuous track without them. Add chapters afterwards in an audiobook tagging tool if you need them.
• "My player still treats it as music" — Some players key off internal metadata rather than the extension, and some sync tools rewrite the extension in transit. Check that the file still ends in .m4b after it reaches the device.
• "An eight-hour recording came out enormous" — The bitrate is set for music. Drop to 64 kbps and Mono for a single narrator; that is roughly 29 MB per hour instead of the 58 MB that 128 kbps costs.
• "It will not import at all" — Some players accept only files that are already tagged as audiobooks internally. Tagging the file usually fixes this without re-encoding it.
• "The first ten seconds are a title card with no sound" — Set Trim to Time Range with a Start time past the silence, so the M4B begins where the speech does.

When This Doesn't Work

Three situations need something other than this page. A book delivered as a dozen separate recordings has to be joined into one continuous file before it becomes a single audiobook — this conversion handles one input at a time and does not concatenate, so stitch the parts together in an audio editor first and convert the result. Purchased audiobooks from a store are usually protected and cannot be re-encoded at all, by us or by anything else, until they are obtained in an unprotected form. And if what you actually want is a smaller version of an M4B you already have rather than a new one from video, compress M4B is the right tool — it takes the existing file and re-encodes it downward without going back to the source.

Frequently Asked Questions

Is an M4B technically different from an M4A?

Not in the bytes that matter. Both are MPEG-4 Part 14 files carrying an AAC audio track, and a player that ignores the extension cannot tell them apart. The difference is entirely convention: the .m4b extension tells Apple Books, Apple Podcasts and dedicated audiobook apps to treat the file as long-form spoken word, which is what makes them remember your position, offer variable-speed playback and keep the file out of your music library. Renaming an .m4a to .m4b changes nothing inside the file and often works, which tells you how thin the technical distinction really is.

Why does my M4B have no chapters?

Because this conversion does not write them. Chapter markers are metadata that has to be authored — someone or something decides where each chapter begins and writes those timestamps into the file — and there is nothing in an H.265 recording that tells the converter where the chapter boundaries are. The container supports chapters perfectly well; the information simply is not there to put in. Add them afterwards with an audiobook tagging tool, which can insert markers without re-encoding the audio.

Why is my output silent?

Almost certainly because the source had no audio. HEVC is a video coding standard — it defines picture compression and specifies nothing about sound — so a true .hevc elementary stream carries no audio track at all. Files from screen recorders, DVRs and raw ffmpeg dumps are like this. The exception is a .hevc written by our own HEVC converters, which is really a Matroska container with the source audio kept, and those extract fine. If yours is a bare stream, the sound is still in the original container file.

What bitrate should I use for a five-hour lecture recording?

64 kbps with Audio Channel set to Mono, unless the recording has music in it. That works out to about 29 MB per hour, so a five-hour lecture lands near 145 MB — comfortable to sync and to keep on a phone. Doubling to 128 kbps doubles that to roughly 290 MB and buys almost nothing on a single speaking voice. If there is applause, music or two people talking over each other, step up to 96 kbps and leave the channel setting on Original.

Will the audio lose quality?

Yes, slightly, because two lossy encodes are involved. The audio inside a video container was compressed once already — usually as AAC — and this conversion decodes it and encodes it again rather than copying it across untouched, which is what makes the bitrate, channel, sample-rate and trim controls possible. For speech, that second pass is essentially inaudible at 64 kbps or above. For music-heavy material, encode at or a little above the source rate so the second generation does not show.

Can I trim the recording down to just the part I want?

Yes, and it is worth doing. Set Trim to Time Range and enter a Start time and a Duration, in plain seconds or as HH:MM:SS.sss. Only that span is decoded and encoded, so a long capture also finishes faster. This is the standard way to strip a title card, a countdown or a long silent lead-in off the front of a recorded talk before it becomes an audiobook.

Will the M4B play on Android, or is it an Apple format?

It plays on Android too. The .m4b convention came from Apple, but the file underneath is ordinary MPEG-4 audio, and the popular Android audiobook players recognise the extension and provide the same resume-position behaviour Apple Books does. Where you can run into trouble is a generic music player that has never heard of the extension and simply ignores the file. If a specific app refuses it, converting to HEVC to M4A instead gives you a file that every audio player will open, at the cost of the audiobook handling.

Should I change the sample rate for a spoken-word file?

Only when the recording is genuinely narrowband to begin with. Resampling cannot add information, and dropping a 48 kHz recording of a lecture hall with applause and room tone to 16 kHz audibly dulls it. For a clean single voice, 24000 Hz is more than enough and trims a little more off the file. If you are unsure, leave Audio Sample Rate on Original and control the size with the bitrate instead — it is the safer of the two levers.

How are my files handled, and how long are they kept?

Your .hevc is uploaded over an encrypted connection, converted on our servers, and the .m4b is returned to you. Uploads and outputs are deleted automatically a few hours after the conversion — no sign-up, no watermark, and files are never shared or made public. On a multi-hour recording the wait is dominated by upload size and connection speed rather than the encode, so trimming the source before uploading is the single most effective thing you can do to speed the job up.