Encoding with ffmpeg and libx264, are there presets or flags that will optimize decoding speed?
Right now it seems that videos transcoded with similar file sizes are decoded at very different speeds using Qtkit, and I was wondering whether there are options for encoding such that the decoding speed will be maximal.
There is --tune fastdecode in x264 (or -tune fastdecode if using ffmpeg) if you want optimize for decoding speed at the cost of quality/compression efficiency. In libx264 tune setting is available as one of the params for x264_param_default_preset.
I've used this in the past:
-b (to remove B Frame calculations)
-maxrate 8M (I find this is important because sometimes the averages have a large distribution in bitrate and so if you set 8M as an average, you may still find 15M peaks)
-tune fastdecode (already explained above)
Related
I am trying to use the hevc_nvenc encoder in ffmpeg to reencode an old video I have. Obviously software encoding using libx265 would be better, but I want to make in fast. I am trying to optimize for video quality, so I am using these options:
-profile:v main -b_ref_mode 0 -preset p7 -tune hq -rc vbr
b_ref_mode 0 since my gpu doesn't support bframe reference mode.
This gives results with average bitrate of around 2M, so I am guessing that is the default bitrate setting for nvenc. Increasing -b:v increases average bitrate, but around 6.5M it stops. Even using -b:v 50M gives the same video bitrate. I have also tried setting -cq 1 to force the best quality possible, but that actually decreases bitrate to around 4.5M. The only way I found to get the desired bitrate is using -cq 1 and -maxrate set to a big value. This removes the restriction, and actually the -b:v option is no longer needed, it seems like it doesn't have any effect at all.
All of this behaviour seems very strange to me, with some hidden default values for bitrate and maxrate, so the question is where can I see these values? I tried using ffmpeg with -loglevel debug but didn't see these values getting passed, and the documentation I found says maxrate default in ffmpeg is 0 (what does this mean?).
I'm using ffmpeg 4.3.1 to convert videos from h264 to h265 and initially I was excited to discover that I can use my Mac's GPU to speed up the conversion with the flag hevc_videotoolbox.
My Mac hardware is the 10th generation Intel i5 with AMD Radeon Pro 5300
I'm using this command:
ffmpeg -i input_h264.mp4 -c:v hevc_videotoolbox -b:v 6000K -c:a copy -crf 19 -preset veryslow output_h265.mp4
The conversion speeds increased from 0.75x to 4x, almost a 500% improvement !
But then I noticed large filesizes and slightly fuzzy results. Then I noticed that changing the crf or the preset makes no difference, ffmpeg seems to ignore those settings. The only setting that seems to work is the video bit rate (-b:v).
So I started to google around to see how I could get better results.
But except for a few posts here and there, I'm mostly coming up blank.
Where can I get documentation on how to get better results using hevc_videotoolbox?
How can I find out what settings work and which ones are ignored?
Use the constant quality mode of videotoolbox on Apple Silicon to achieve high speed, high quality and small size. This works from FFmpeg 4.4 and higher — it's based on this commit.
Note that this does not work with Rosetta 2.
Compile ffmpeg for macOS or use ffmpeg from Homebrew (brew install ffmpeg)
Run with -q:v 65. The value should be 1-100, the higher the number, the better the quality. 65 seems to be acceptable.
For example:
ffmpeg -i in.avi -c:v hevc_videotoolbox -q:v 65 -tag:v hvc1 out.mp4
Listing options
Run ffmpeg -h encoder=hevc_videotoolbox to list options specific to hevc_videotoolbox.
Use -b:v to control quality. -crf is only for libx264, libx265, libvpx, and libvpx-vp9. It will be ignored by other encoders. It will also ignore -preset.
hevc_videotoolbox isn't as good as libx265, but it is fast
Like most hardware accelerated encoders, hevc_videotoolbox is not as efficient as libx265. So you may have to give it a significantly higher bitrate to match an equivalent quality compared to libx265. This may defeat the purpose of re-encoding from H.264 to HEVC/H.265.
Avoid re-encoding if you can
Personally, I would avoid re-encoding to prevent generation loss unless the originals were encoded very inefficiently and drive space was more important.
VideoToolBox can only use the -b:v setting. The crf is ignored. You can run a few test encodes and get an idea what video bitrate is "equivalent" to the CF you desire, then use that bit rate.
Currently I am using this command to convert
ffmpeg -i <srcfile> -vcodec libx264 -profile:v main -level 3.1 -preset slower -crf 18 -x264-params ref=4 -acodec copy -movflags +faststart <outfile>
to convert some dashcam footage for viewing on an iOS device.
The above command took about 30 min to complete on a 2017 Macbookpro with 16G of RAM.
I want to speed it. One thing I tried is to harness the GPU in the computer. Therefore I added the flag -c:v h264_videotoolbox
It sped up by a lot. I can complete the conversion in 1 min.
However, when I inspected the output, the GPU version suffers from banding and blurry.
Here is a screenshot. CPU version on the left and GPU version on the right.
To highlight the difference, here are the parts of the videos
Trees in reflections
corrugated iron sheet wall
Is there any switch that I can manipulate to make the GPU version clearer?
This is a simplistic H.264 encoder compared to x264, so you're not going to get the same quality per bitrate. h264_videotoolbox is optimized for speed and does not support -crf.
You can view some options specific to this encoder with ffmpeg -h encoder=h264_videotoolbox, but as they are probably already set to "auto" (I didn't confirm via source code and I don't have the hardware to try it) these additional options may not make much of a difference.
So you'll just have to increase the bitrate, such as with -b:v 8000k.
Or continue to use libx264 with a faster -preset.
I see the question's been answered and nearly two years ago. Jumping in for others who might stumble on the thread. I get great results with VideoToolbox as encoder, using either GPU or software to accelerate, depending which machine I am using.
As already mentioned, setting a constant bitrate, and adjusting it upward is key to producing a result that is nearly indistinguishable from a large source file. A constant bitrate is as effective as two-pass encoding for high-quality output, when paired with other key parameters, and is much quicker than two-pass.
May seem counter-intuitive, but a computer running on all threads, full throttle, to encode a video won't give you best results. Several researchers have demonstrated that quality actually goes down if all cpu threads are engaged in encoding; better to use fewer threads and even throttle ffmpeg with a 3rd party app (encoding does not slow down significantly, in my experience). So limit threads on newer multithread desktops and laptops.
Common practice for target bitrates (seen on Netflix, Amazon) vary with resolution, naturally: at least 5,000kbps for 1080p; 3,500 for 720p. For a noticeable improvement in video quality, the encoder bitrate should be set to at least 1.5 times those common practice bitrates: ie, 7,500 for 1080p, 5,250 for 720p. Similarly for 4K GoPros or dash cams.
Often I work with large movie files from my bluray library, and create slimmed-down versions that are 1/3 to 1/2 the size of the original (20G original gives way to a file of 8-10GB with no perceptible loss of quality. Also: framerate. Maintaining the same framerate from source to slimmed-down file is essential, so that parameter is important. Framerate is either 24fps, 25fps, or 30fps for theatrical film, European tv, and North American tv, respectively. (Except in transferring film to a tv screen, 24fps becomes 23.976fps, in most cases.) Of course 60fps is common for GoPro-like cameras, but here 30fps would be a reasonable choice.
It is this control of framerate and bitrate the keeps ffmpeg in check, and gives you predictable, repeatable results. Not an errant, gigantic file that is larger than the one you may have started with.
I work on a Mac, so there may be slight differences on the command line, and here I use VideoToolbox as software encoder, but a typical command reads:
ffmpeg -loglevel error -stats -i source.video -map 0:0 -filter:v fps\=24000/1001 -c:v h264_videotoolbox -b:v 8500k -profile 3 -level 41 -coder cabac -threads 4 -allow_sw:v 1 -map 0:1 -c:a:0 copy -disposition:a:0 default -map 0:6 -c:s:0 copy -disposition:s:0 0 -metadata:g title\=“If you want file title in the metadata, goes here” -default_mode passthrough ‘outfile.mkv’
-loglevel error (to troubleshoot errors)
-stats (provides progess status in terminal window)
-i infile (source video to transcode)
-map 0:0 (specify each stream in the original to map to output)
-filter:v fps\=24000/1001 (framerate of 23.976, like source)
-c:v h264_videotoolbox (encoder)
-b:v (set bitrate, here I chose 8500k)
-profile 3 -level 41 (h264 profile high, level 4.1)
-coder cabac (cabac coder chosen)
-threads 4 (limit of 4 cpu threads, of 8 on this laptop)
-allow_sw:v 1 (using VideoToolbox software encoding for accleration; GPU is not enabled)
-map 0:1 -c:a:0 copy -disposition:a:0 default (copies audio stream over, unchanged, as default audio)
-map 0:6 -c:s:0 copy -disposition:s:0 0 (copies subtitle stream over, not as default ... ie, will play subtitles automatically)
-metadata:g (global metadata, you can reflect filename in metadata)
-default_mode passthrough (allow audio w/o further processing)
outfile (NOTE: no dash precedes filename/path. Chose mkv format to
hold my multiple streams; mp4 or other formats work just fine ... as
long as contents are appropriate for format.)
In addition of llogan's answer I'd recommend set 'realtime' property to zero (this can increase quality in motion scenes)
As llogan says, bitrate option is good parameter in this situation.
ffmpeg -i input.mov -c:v h264_videotoolbox -b:v {bitrate} -c:a aac output.mp4
if you want to set 1000kb/s bitrate, command is like this
ffmpeg -i input.mov -c:v h264_videotoolbox -b:v 1000k -c:a aac output.mp4
When I transcode video to H265 with following command, I get a bitrate about 600K and the quality is almost the same as the original.
ffmpeg -i data2.mp4 -c:v libx265 -c:a copy d2.mp4
However when I use the hevc_nvenc, I get a very high bitrate (about 2M), I need to have a bitrate as low as possible and keeping almost the same quality.
ffmpeg -i data2.mp4 -c:v hevc_nvenc -c:a copy d3.mp4
It works if I specify the output bitrate, but I want to know how to figure out the proper bitrate?
There is no such thing as "proper bitrate". You get to choose the bitrate. if you don't, the encoder will choose on for you. In this case, you are using two different encoders, so you get different bitrates. You can change this by adding -b:v option to ffmpeg.
But that's probably not what you want. You probably want to use a constant quality factor by setting -crf to a value between 0 (Great quality large file) to 51 (bad quality small file)
Note that hevc_nvenc will almost produce larger files than libx265 at a given quality because it not as efficient as an encoder.
I need convert MP4 to webm with ffmpeg.
So, i use :
ffmpeg -i input.mp4 -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis output.webm
But it's very long.
Is there faster ?
libvpx is a relatively slow encoder. According to the VP8 Encode Parameter Guide: Encode Quality vs. Speed, you can use the -cpu-used option to increase encoding speed. A higher value results in faster encoding but lower quality:
Setting a value of 0 will give the best quality output but is
extremely slow. Using 1 (default) or 2 will give further significant
boosts to encode speed, but will start to have a more noticeable
impact on quality and may also start to effect the accuracy of the
data rate control. Setting a value of 4 or 5 will turn off "rate
distortion optimisation" which has a big impact on quality, but also
greatly speeds up the encoder.
Alternatively, it appears that VA-API can be utilized for hardware accelerated VP8 encoding, but I have no experience with this.