Free ac3 codec for mac

Default value is -1 which means infinity or until the next subtitle event comes. Force transparent background of the generated teletext bitmaps. Default value is 0 which means an opaque background.


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Sets the opacity of the teletext background. When you configure your FFmpeg build, all the supported native encoders are enabled by default. Encoders requiring an external library must be enabled manually via the corresponding --enable-lib option. You can list all available encoders using the configure option --list-encoders. This encoder also implements more options, profiles and samplerates than other encoders with only the AAC-HE profile pending to be implemented so this encoder has become the default and is the recommended choice.

Setting this automatically activates constant bit rate CBR mode. If this option is unspecified it is set to kbps. Set quality for variable bit rate VBR mode. This option is valid only using the ffmpeg command-line tool. Set cutoff frequency.

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If unspecified will allow the encoder to dynamically adjust the cutoff to improve clarity on low bitrates. This method first sets quantizers depending on band thresholds and then tries to find an optimal combination by adding or subtracting a specific value from all quantizers and adjusting some individual quantizer a little. This is an experimental coder which currently produces a lower quality, is more unstable and is slower than the default twoloop coder but has potential. Not currently recommended. Worse with low bitrates less than 64kbps , but is better and much faster at higher bitrates.

This is the default choice for a coder.

Can be forced for all bands using the value "enable", which is mainly useful for debugging or disabled using "disable". Sets intensity stereo coding tool usage. Can be disabled for debugging by setting the value to "disable". Uses perceptual noise substitution to replace low entropy high frequency bands with imperceptible white noise during the decoding process.

Enables the use of a multitap FIR filter which spans through the high frequency bands to hide quantization noise during the encoding process and is reverted by the decoder. As well as decreasing unpleasant artifacts in the high range this also reduces the entropy in the high bands and allows for more bits to be used by the mid-low bands. Enables the use of the long term prediction extension which increases coding efficiency in very low bandwidth situations such as encoding of voice or solo piano music by extending constant harmonic peaks in bands throughout frames.

Use in conjunction with -ar to decrease the samplerate. Enables the use of a more traditional style of prediction where the spectral coefficients transmitted are replaced by the difference of the current coefficients minus the previous "predicted" coefficients. In theory and sometimes in practice this can improve quality for low to mid bitrate audio. The default, AAC "Low-complexity" profile. Is the most compatible and produces decent quality. Introduced in MPEG4. Introduced in MPEG2.


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  4. This does not mean that one is always faster, just that one or the other may be better suited to a particular system. The floating-point encoder will generally produce better quality audio for a given bitrate. The AC-3 metadata options are used to set parameters that describe the audio, but in most cases do not affect the audio encoding itself. Some of the options do directly affect or influence the decoding and playback of the resulting bitstream, while others are just for informational purposes.

    A few of the options will add bits to the output stream that could otherwise be used for audio data, and will thus affect the quality of the output. Those will be indicated accordingly with a note in the option list below. Allow Per-Frame Metadata.

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    Specifies if the encoder should check for changing metadata for each frame. Center Mix Level. The amount of gain the decoder should apply to the center channel when downmixing to stereo. This field will only be written to the bitstream if a center channel is present. The value is specified as a scale factor. There are 3 valid values:. Surround Mix Level. The amount of gain the decoder should apply to the surround channel s when downmixing to stereo.

    This field will only be written to the bitstream if one or more surround channels are present. Audio Production Information is optional information describing the mixing environment. Either none or both of the fields are written to the bitstream. Mixing Level. Specifies peak sound pressure level SPL in the production environment when the mix was mastered.

    Valid values are 80 to , or -1 for unknown or not indicated. The default value is -1, but that value cannot be used if the Audio Production Information is written to the bitstream. Room Type. Describes the equalization used during the final mixing session at the studio or on the dubbing stage. A large room is a dubbing stage with the industry standard X-curve equalization; a small room has flat equalization.

    Dialogue Normalization.

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    This parameter determines a level shift during audio reproduction that sets the average volume of the dialogue to a preset level. The goal is to match volume level between program sources. A value of dB will result in no volume level change, relative to the source volume, during audio reproduction. Valid values are whole numbers in the range to -1, with being the default. Dolby Surround Mode. Specifies whether the stereo signal uses Dolby Surround Pro Logic.

    This field will only be written to the bitstream if the audio stream is stereo. Original Bit Stream Indicator. Specifies whether this audio is from the original source and not a copy. It is grouped into 2 parts.

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    If any one parameter in a group is specified, all values in that group will be written to the bitstream. Default values are used for those that are written but have not been specified. Preferred Stereo Downmix Mode. Dolby Surround EX Mode. Indicates whether the stream uses Dolby Surround EX 7. Dolby Headphone Mode.

    Indicates whether the stream uses Dolby Headphone encoding multi-channel matrixed to 2. Stereo Rematrixing. This option is enabled by default, and it is highly recommended that it be left as enabled except for testing purposes. Set lowpass cutoff frequency. If unspecified, the encoder selects a default determined by various other encoding parameters. These options are only valid for the floating-point encoder and do not exist for the fixed-point encoder due to the corresponding features not being implemented in fixed-point.

    The per-channel high frequency information is sent with less accuracy in both the frequency and time domains. This allows more bits to be used for lower frequencies while preserving enough information to reconstruct the high frequencies. This option is enabled by default for the floating-point encoder and should generally be left as enabled except for testing purposes or to increase encoding speed. Coupling Start Band. Sets the channel coupling start band, from 1 to If a value higher than the bandwidth is used, it will be reduced to 1 less than the coupling end band.

    If auto is used, the start band will be determined by the encoder based on the bit rate, sample rate, and channel layout. This option has no effect if channel coupling is disabled. Sets the compression level, which chooses defaults for many other options if they are not set explicitly.

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    Valid values are from 0 to 12, 5 is the default. Chooses if rice parameters are calculated exactly or approximately. Multi Dimensional Quantization. If set to 1 then a 2nd stage LPC algorithm is applied after the first stage to finetune the coefficients. This is quite slow and slightly improves compression. This is a native FFmpeg encoder for the Opus format.