HomePage 3 of 8: x264 Options: Common
Mode:
Description: Selects the encoding mode to be used by the encoder. Single pass encoding can give unexpected output file sizes (Quantizer and Quality modes) and/or poorer quality compared to multi pass encoding.
Available Options:
Single Pass - Bitrate: Encodes the video once (single pass) with a set constant bitrate for each frame
Single Pass - Quantizer: Single pass encoding with a set quantizer (higher quantizer => lower quality) for each frame
Single Pass - Quality: Single pass encoding with a set quality rating for each frame
Two Pass: Encodes the video twice (once to determine it's properties, another to ensure the selected output file size is reached with maximum efficiency). This is the most common setting.
Three Pass: Same as Two Pass except for an extra encoding pass to ensure even better quality/accurate file size
Command Line: --bitrate, --qp, --crf, --pass 1/2/3
Quantizer:
Description: Only available with "Single Pass - Quantizer" mode is selected. Set the quantizer value for the encoding. A high quantizer will equal a low quality (and smaller file size). A quantizer value between 20 (high quality) and 30 (low quality) should be used. Anime/cartoons or scenes with large patches of color or less details benefit from having a higher quantizer, typical movies require a lower quantizer.
Command Line: --qp n
(where 'n' is the quantizer value)
Quality:
Description: Only available with "Single Pass - Quality" mode is selected. Set the quality value for the encoding. A high quality value equals a higher quality encoding (and larger file size).
Command Line: --crf n
(where 'n' is the quality value)
B-Frames:
Description: Selects the number of consecutive B-frames x264 should use. It is also the maximum number of consecutive B-frames x264 can use if the "Adaptive" B-frames option (see next section) is selected. B-frames are frames that are small in size, but when placed correctly, offer no loss of quality. This can help improve compression. With the "Adaptive" option on (x264 will decide how many B-frames to use), having a setting of 3 is recommended as this gives x264 enough room to work with.
Command Line: --bframes n
(where 'n' is the number of B-frames)
Reference Frames:
Description: Selects the maximum number of reference frames that can be used. Referenced frames are frames that refer to other frames (eg. if both frames are similar). Having a high referenced frame will improve quality but slow up encoding. For typical content, a reference frame of 3 to 5 is recommended. For content with a lot of repetition (eg. animation), a reference frame of 8 to 10 can be used. If a large number of reference frames is selected, then the "Mixed References" options should also be selected to allow x264 greater control (see "Analysis Options" section).
Command Line: --ref n
(where 'n' is the number of reference frames)
Loop Filter:
Description: Also known as "de-blocking" filter. Connected with the "Alpha" and "Beta" setting next to it. One of the fundamental differences between H.264 and previous codecs. Should always be enabled or excessive video artifacts may appear. Controversial because blocking (when the video looks like a series of different colored squares in low bitrate video) and artifacts are treated as details by the human visual system, and removing them makes people think details is lost, when it's actually the other way around (more "actual" details shown due to less artifacts). This is an interesting topic that is better discussed in DeathTheSheep's x264 guide.
Command Line: --nf
(disables loop filter)
Alpha/Beta:
Description: This controls the "Loop Filter" (see above). Also known as Strength (Alpha) and Threshold (Beta). Alpha determines the strength of the deblocking action. Beta determines when x264 decides something is a block and when something isn't - a high value means x264 sees more video as blocks than a lower value. For example, a too high Beta value and a too high Alpha means x264 will identify too many blocks (even when they aren't artifacts) and apply too much filtering to remove them, making the picture look "washed out" and lacking detail. Both values can be positive or negative. 0/0 (Alpha/Beta) is the default and recommended setting, unless you find the video quality unacceptable, then you should try combinations. Do not go under -2 or above 3. This is an interesting topic that is better discussed in DeathTheSheep's x264 guide.
Command Line: --filter
