Mplayerx 7.1 acc1/27/2024 Target a quality, rather than a specific bit rate. ac 2 -c:a libfdk_aac -b:a 128k output.mp4 As a rule of thumb, for audible transparency, use 64 kBit/s for each channel (so 128 kBit/s for stereo, 384 kBit/s for 5.1 surround sound).Ĭonvert an audio file to AAC in an M4A (MP4) container:įfmpeg -i input.wav -c:a libfdk_aac -b:a 128k output.m4aĬonvert 5.1 surround sound audio of a video, leaving the video alone:įfmpeg -i input.mp4 -c:v copy -c:a libfdk_aac -b:a 384k output.mp4Ĭonvert the video with libx264, with a target of fitting a 90-minute movie on a 700 MB (=5734400 KB) CD-ROM, mixing the audio down to two channels (Windows users should use NUL rather than /dev/null and ^ instead of \):įfmpeg -y -i input.mp4 -c:v libx264 -b:v 933k -preset:v veryfast -pass 1 -an /dev/null & \įfmpeg -i input.mp4 -c:v libx264 -b:v 933k -preset:v veryfast -pass 2 \ It gives you greater control over file size, and it is compatible with the HE-AAC profile. These settings target a specific bit rate, with less variation between samples. Adjust the number to the upper frequency limit only if you need to keeping in mind that a higher limit may audibly reduce the overall quality. If you want to preserve higher frequencies, use -cutoff 18000. Note: libfdk_aac defaults to a low-pass filter of around 14kHz ( details). Requires ffmpeg to be configured with -enable-libfdk-aac (and additionally -enable-nonfree if you're also using -enable-gpl).ĭetailed information about the FDK AAC library (not FFmpeg specific) can be found at HydrogenAudio Knowledgebase: Fraunhofer FDK AAC. This is currently the highest-quality AAC encoder available with ffmpeg (except on macOS, see below). See also Encode/HighQualityAudio for general guidelines on FFmpeg audio encoding (which also includes a comparison of which AAC encoder is best quality). This can be resolved by compiling ffmpeg yourself. Therefore this encoder have been designated as "non-free", and you cannot download a pre-built ffmpeg that supports it. The license of libfdk_aac is not compatible with GPL, so the GPL does not permit distribution of binaries containing incompatible code when GPL-licensed code is also included. The examples in this guide will use the extensions MP4 and M4A.įFmpeg supports three AAC-LC encoders ( aac, libfdk_aac, aac_at) and two HE-AAC (v1/2) encoder ( libfdk_aac, aac_at). The second-most common use is within MKV (Matroska) files because it has better support for embedded text-based soft subtitles than MP4. It is often used within an MP4 container format for music the. Advanced Audio Coding (AAC) is the successor format to MP3, and is defined in MPEG-4 part 3 (ISO/IEC 14496-3).
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