This is particularly useful for online streaming, where the client expects a certain average bitrate, but you still want the encoder to adjust the bitrate per-frame.
You can use -crf or -b:v with a maximum bit rate by specifying both -maxrate and -bufsize :. However, be aware that libx does not strictly control the maximum bit rate as you specified the maximum bit rate may be well over 1M for the above file. To reach a perfect maximum bit rate, use two-pass. In another example, instead of using constant quality CRF as a target, the average bitrate is set. A two-pass approach is preferred here:. This will move some information to the beginning of your file and allow the video to begin playing before it is completely downloaded by the viewer.
It is not required if you are going to use a video service such as YouTube. Refer to the -vpre output option in the documentation. It will give a slight encoding speed boost using GPU, without hurting quality. You will see Compiling OpenCL kernels This depends on the source material, the target bitrate, and your hardware configuration.
In general, the higher the bitrate, the more time needed for encoding. Here is an example that shows the normalized encoding time for a two-pass encode of a p video:. Use -c:v libxrgb instead. These players only support the YUV planar color space with chroma subsampling for H. Otherwise, depending on your source, ffmpeg may output to a pixel format that may be incompatible with these players. Download all attachments as:.
Powered by Trac 1. Last modified 8 months ago Last modified on Mar 11, , PM. Note: See TracWiki for help on using the wiki. As far as I remember I read in the past that 2-pass encoding increases significantly the output quality.
Did I miss something? Originally Posted by mike Originally Posted by Groucho It depends on to what you compare it. Compared to CRF mode given the same bitrate , the answer is no. Originally Posted by Stereodude. A 2 pass encoding should have the same image quality as a CRF encode of the same size.
It should also be better than a 1 pass encode of the same size in the more demanding scenes, but will be worse in the simple scenes. Also, the bold part of your statement below is misleading: There are settings to optimise bitrate distribution in CRF encodes, one does not have to resort to a far inferior CBR mode.
No, it's not misleading. It is accurate. A 2 pass encoding at the same average bitrate will be worse in simple scenes than a 1 pass CBR encoding presuming there are scenes of varying complexity. Your comment about bitrate optimization of CRF modes has nothing to do with the statement I made. I don't know if it has an effect on the quality, but there is one difference i've noticed between CRF and 2-pass encoding.
If you look at the log file, with a CRF encode, or on the 1rst pass of a 2-pass encode, you'll always have at least it's my case : Code:. Originally Posted by jpsdr.
I don't know what is the effect, and if it also affect the bit allocation, but according this result, the 2nd pass obviously doesn't produce the same result than CRF, and for now, i wouldn't say also the bit allocation is identical But, i may be wrong also, as i don't know what is the effect of the bit allocation between a Originally Posted by amichaelt.
I used CRF 22 for all the three movies The source is untouched Bluray original disc , and ended with bitrates I mentioned. Also I could see that the two movies with low bitrates looked low quality compared to The Dark Knight which ended with a high bitrate and a better quality as perceived by the eye.
If all three were encoded with the same CRF and all other settings were the same for all three, the final bitrates are meaningless and all three videos should appear the same visually. If you didn't like that appearance, then use a lower CRF. Making them for the same bitrate isn't the way to give them all the same quality. I suppose it's possible the source Blu-Rays had wildly differing qualities, which might account for what you're seeing, but there's no way for someone reading your thread to know that.
Maybe check out some reviews of the Blu-Rays to see if any reviewers noticed any differences in quality. Okay, thanks. I'll try encoding again. I can't begin to tell you how many times I have seen somebody complain about the quality of something simply because of doing something like that. They look at something like the bitrate of a file, see it is much lower than another file, and then somehow "see" a difference in the video quality because of their expectation the file will be of worse quality, then I look at the files and they are virtually indistinguishable.
Maybe there really is a difference in the visual quality of your rips, maybe not. All I'm saying is eliminate your expectations as a possibility of why you are seeing a difference first, then worry about bitrate. I'm aware that this thread is days old but no one mentioned the difference of keyframe placement my favorite so I wanted to add it. You can even re-arrange scenes with stream-copy.
In single pass, encoder does not scout for bitrate demand before encoding so it can not optimize according to scene changes. Originally Posted by noisywan. Replies: 10 Last Post: 22nd Jul , Replies: 8 Last Post: 21st Sep , Replies: 4 Last Post: 26th Nov , Replies: 0 Last Post: 17th Jan , Two Pass encoding?
Replies: 4 Last Post: 19th Jun , Contact Us VideoHelp Top. In the second pass, the collected data from the first pass is used to achieve the best encoding quality. In video encoding, two-pass encoding is usually controlled by the average bitrate setting or by the bitrate range setting minimal and maximal allowed bitrate or by the target video file size setting.
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