I don't understand what these options ( -r 30 -s 1280x720 -preset superfast -profile:v baseline) mean , searched but couldn't find , hope someone can help :
ffmpeg -i rtmp://localhost:1935/stream/$name
-c:a libfdk_aac -b:a 128k -c:v libx264 -b:v 2500k -f flv -g 30 -r 30 -s 1280x720 -preset superfast -profile:v baseline rtmp://localhost:1935/hls/$name_720p2628kbs
From https://ffmpeg.org/ffmpeg.html
-r[:stream_specifier] fps (input/output,per-stream)
Set frame rate (Hz value, fraction or abbreviation).
-s[:stream_specifier] size (input/output,per-stream)
Set frame size.
From https://trac.ffmpeg.org/wiki/Encode/H.264
Preset
A preset is a collection of options that will provide a certain encoding speed to compression ratio. A slower preset will provide better compression (compression is quality per filesize). This means that, for example, if you target a certain file size or constant bit rate, you will achieve better quality with a slower preset. Similarly, for constant quality encoding, you will simply save bitrate by choosing a slower preset.
Profile
The -profile:v option limits the output to a specific H.264 profile. You usually do not need to use this option and the recommendation is to omit setting the profile which will allow x264 to automatically select the appropriate profile.
Related
I wanted to encode a video file which was initially encoded by a libx264 encoder on a non gpu machine with ultrafast preset and crf 23 , i typically re-encode it with preset medium and get a good compression but the process is very slow , so i am considering a gpu based solution
my current command to use ffmpeg on a nvidia turing gpu
ffmpeg -y -vsync passthrough -hwaccel cuda -i a.mp4 -max_muxing_queue_size 9999 -pix_fmt yuv420p -c:v h264_nvenc -preset medium -tune ll -b:v 4M -bufsize 4M -maxrate 10M -qmin 0 b.mp4
usual command i use to do the same
ffmpeg -i a.mp4 -max_muxing_queue_size 9999 -pix_fmt yuv420p -c:v libx264 -preset medium b.mp4
enter code here
How can i make this command do a better job at reducing file size , i am okay to compromise on the quality of the video for a good reduction in size
I would highly recommend reading this H.264 Video Encoding Guide
On the surface, these variants can help you:
Decrease your bitrate
Add -cq option with suitable value 0-51 (-cq for h264_nvenc is pretty the same as -crf for libx264)
Change -tune option value to hq
Try two-pass encoding (if you know desired output file size), but here is very low benefit
If you struggle with available options for h264_nvenc you can see the whole list of them by executing following command:
ffmpeg -hide_banner -h encoder=h264_nvenc
Most of them are self descriptive or similar from libx264
Currently I am using this...
ffmpeg -video_size 1920x1080 -framerate 1 -f x11grab -i :0.0+0,0 -f pulse -ac 2 -i default -t 00:00:10 Output.mkv
While ffmpeg is recording a video, I want it to significantly reduce both the size and quality compared to the ffmpeg command above.
In case you are curious, I am recording brief quality assurance videos to ensure a simple little web scraper I wrote in Python is scraping data properly (specifically, that it is clicking on a particular button, at a particular time, on a particular web page). My Python script triggers the command above to start recording my screen a few seconds before my Python script is supposed to click on that button.
Of course, to verify a button on a web page had been clicked on, low quality video resolution would normally suffice.
For libx264/libx265 the most important option to reduce both the size and quality is -crf. This option controls quality. A value of 51 provides the worst quality. If it's too terrible then use a lower number.
ffmpeg -video_size 1920x1080 -framerate 1 -f x11grab -i :0.0+0,0 -f pulse -channels 2 -i default -t 00:00:10 -c:v libx264 -crf 51 -c:a libopus Output.mkv
See FFmpeg Wiki: H.264.
For significantly reduce both the size and quality of Output.mkv you can use the next ffmpeg configuration:
crop: iw-(cut width in pixels):ih-(cut heigth in pixels)
scale: to set the ratio and resolution (example 1700x800)
crf: to set quality, where 0 is lossless, 23 is default, and 51 is worst possible. A lower value is a higher quality and a subjectively sane range is 18-28. Consider 18 to be visually lossless
bitrate value: -b:v value -minrate value and -maxrate max value (example -b:v 4000K -minrate 2000K -maxrate 6000K)
preset: in theory slow is best quality/size, and you can probe ultrafast
superfast
veryfast
faster
fast
medium – default preset
slow
slower
veryslow
Cut a part of video, changue the resolution, changue crf, and bitrate, first only video, then you can add audio in other work, dont mix, repeat, is very important, encoding/decoding audio and video separate, then you can mix all, but first the video like in this example
ffmpeg -i Output.mkv -map 0:v -vf crop=iw-150:ih-85,scale=ih*16/9:ih,scale=1072:732,setsar=1 -c:v libx264 -crf 17 -b:v 4000K -maxrate 6000K -bufsize 4M -movflags -faststart -preset veryfast -dn video-new.mkv
Could someone explain what -crf means in the following command:
ffmpeg -i input.mp4 -c:v libx264 -crf 65 -b:v 1M -c:a aac output.mp4
What does -crf stand for?
CRF (Constant Rate Factor) is the default quality setting for the x264 and x265 encoders. You can set the values between 0 and 51, where :
lower values would result in better quality, at the expense of higher file sizes.
Higher values mean more compression, but at some point, you will notice the quality degradation.
You can also read about the Quantization Parameter which controls the amount of compression for every Macroblock in a frame
this is how I use FFmpeg
ffmpeg -f dshow -i video="UScreenCapture" -vcodec libx264 -q 26 -f flv output.flv
the thing is, the quantity is always 28, ffmpeg ignores that. How to fix this? I need a "flash" codec anyway, to stream to twitch tv
The options -q (and the alias -qscale) are ignored by libx264. If you want to
control the quality,
use:
-crf
ffmpeg -i input -c:v libx264 -crf 22 output.flv
Or set the bitrate with -b:v
ffmpeg -i input -c:v libx264 -b:v 555k output.flv
According to the documentation, "the meaning of q is codec-dependent" and apparently libx264 ignores that option. Use -crf (and a -preset if you want) instead. The bigger the crf value, the lower the quality.
if you wish to generate CQP (constant QP stream), e.g for constant QP=20 i suggest using the following parameters:
'x264-params qp=20:ipratio=1.0:pbratio=1.0:qpstep=0'
Example:
ffmpeg -s 1920x1080 -i test.yuv -vcodec libx264 -x264-params qp=20:ipratio=1.0:pbratio=1.0:qpstep=0 -y test.h264
Notice that 'ipratio=1.0' makes x264 to encode P frame with same QP as I-frame and 'pbratio=1.0' makes x264 to encode B-frame with same QP as P-frame.
The -b options, -q, and -crf seem to do nothing for video qualtiy (at least for my install of ffmpeg version 9), so I am posting a result from another post that gets right to the point
If you want high quality, setting bitrate is a poor way to achieve that. There are many other settings with far bigger influence on quality than bitrate. I would leave the bitrate setting out entirely unless you are having to meet hardware requirements of some sort.
If you are trying to get higher quality, try something like
ffmpeg -i sourcefile.mov -target pal-dvd -qscale 2 -trellis 2 outputfile.mpg
output video size goes from 13Mb for a 2 min video to 130Mb, but it gets the job done.
I'm dealing with a very big issue about bit rate , ffmpeg provide the -b option for the bit rate and for adjustment it provide -minrate and -maxrate, -bufsize but it don't work proper. If i'm giving 256kbps at -b option , when the trans-coding finishes , it provide the 380kbps. How can we achieve the constant bit rate using ffmpeg. If their is +-10Kb it's adjustable. but the video bit rate always exceed by 50-100 kbps.
I'm using following command
ffmpeg -i "demo.avs" -vcodec libx264 -s 320x240 -aspect 4:3 -r 15 -b 256kb \
-minrate 200kb -maxrate 280kb -bufsize 256kb -acodec libmp3lame -ac 2 \
-ar 22050 -ab 64kb -y "output.mp4"
When trans-coding is done, the Media Info show overall bit rate 440kb (it should be 320kb).
Is their something wrong in the command. Or i have to use some other parameter? Plz provide your suggestion its very important.
Those options don't do what you think they do. From the FFmpeg FAQ:
3.18 FFmpeg does not adhere to the -maxrate setting, some frames are bigger than
maxrate/fps.
Read the MPEG spec about video buffer verifier.
3.19 I want CBR, but no matter what I do frame sizes differ.
You do not understand what CBR is, please read the MPEG spec. Read
about video buffer verifier and constant bitrate. The one sentence
summary is that there is a buffer and the input rate is constant, the
output can vary as needed.
Let me highlight a sentance for you:
The one sentence summary is that there is a buffer and the input rate is constant, the output can vary as needed.
That means, in essence that the -maxrate and other settings don't control the output stream rate like you thought they did.