Content
Lossless Encoding with x264 and ffmpeg
How Add AUDs (Access Unit Delimiters)
Free H264 High Level Stream Analyzer
Note:
Binaries for all platforms of x264 are located at https://download.videolan.org/x264/binaries/
Lossless Encoding with x264 and ffmpeg
To instruct x264 to make lossless encoding use the following switches: '--qp 0' and '--no-8x8dct'
Example of lossless encoding :
x264 --qp 0 --input-res 352x288 --no-8x8dct --output container_352x288_lossless.h264 container_352x288.yuv
To verify that the output stream is indeed lossless one can apply ffmpeg decoding:
ffmpeg -i container_352x288_lossless.h264 -vcodec rawvideo -pix_fmt yuv420p -y lossless.yuv
It’s worth mentioning that unlike to ffmpeg, JM18 produces near-lossless output of the given stream (container_352x288_lossless.h264). Why?
Another possibility is to use ffmpeg libx264 encoder with ‘-crf 0’ :
ffmpeg -s 1920×1080 -i test.yuv -c:v libx264 -crf 0 -y output.h264
Constant QP Encoding
To generate constant QP stream set the following command line parameters: '--qp <n> --ipratio 1.0 --pbratio 1.0 --qpstep 0'
Example of constant QP encoding (QP=20) :
x264 --qp 20 --ipratio 1.0 --pbratio 1.0 --qpstep 0 --input-res 352x288 --output qp20.h264 container_352x288.yuv
Notice that qp-modulation (aq-mode) is implicitly switched off by x264 in case of constant qp (i.e. if –qp <n> is present).
Constant Quality Mode (CRF)
Visual quality is controlled by ‘-crf’ parameter, lesser crf-value better quality. Reasonable values are in the range 18-28.
Example of encoding in CRF mode:
ffmpeg -s 1920x1080 -i test.yuv -c:v libx264 -crf 25 output.h264
Number Reference Frames
i found that in x264 the option ‘--ref 4’ (four reference frames) option increases significantly encoding time comparing to that with ‘--ref 3’:
x264 settings:
CRF:
--threads 1 --keyint infinite --no-scenecut --muxer raw --open-gop --qpmax 45 --no-interlaced --bframes 3 --crf 25 --weightb --qcomp 0.6 --no-mixed-refs --ipratio 1.408 --chroma-qp-offset 0 --aq-strength 0.7 --qpstep 4 --qpmin 10 --8x8dct --profile high --input-res 1920x1080 --output test.264 --aud --slices 4 --force-cfr --fps 24000/1001 --sar 1:1 --pic-struct --force-pps-qp 26 --poc-diff 1 --trellis 1 --merange 16 --subme 7 --deadzone-inter 21 --me hex --partitions i4x4,i8x8,p8x8,b8x8 --weightp 1 --direct auto --deadzone-intra 11
VBR:
--threads 1 --keyint infinite --no-scenecut --muxer raw --open-gop --qpmax 45 --no-interlaced --bframes 3 --weightb --qcomp 0.6 --no-mixed-refs --ipratio 1.4 --chroma-qp-offset 0 --qpstep 4 --qpmin 10 --8x8dct --output test.h264 --profile high --input-res 1920x1080 --aud --slices 4 --fps 24000/1001 --sar 1:1 --pic-struct --force-pps-qp 26 --poc-diff 1 --trellis 1 --aq-strength 0.7 --merange 16 --subme 7 --deadzone-inter 21 --me hex --partitions i4x4,i8x8,p8x8,b8x8 --weightp 1 --direct auto --deadzone-intra 11 --rc-lookahead 40 --no-mbtree --b-adapt 0 --b-pyramid normal --sps-id 0 --bitrate 10965
A switch from ‘--ref 3’ to '--ref 4’ increases significantly encoding times. According to my evaluations the switch from ‘--ref 3’ to '--ref 4’ does not provide a significant gain in coding efficiency.
Note: Perhaps that x264 setting i used is sub-optimal (e.g. ‘umh’ is better than ‘hex’, but ‘umh’ is more time-consuming). i applied same setting with '--ref 3' and '--ref 4' and obtained negligible gain in coding efficiency and significant penalty in encoding times.
How Add AUDs (Access Unit Delimiters)
AUDs are useful since this NAL unit (the type = 9) delimiters video frames, it’s easy to edit, process and play video streams with AUDs. The AUD NAL unit is too short ( 6 bytes, 00 00 00 01 09 10) to add any significant overhead onto the stream. ffmpeg has an option “-x264opts aud=1” to add AUDs at the start of each frame.
Example:
ffmpeg -y -i .\yuv\battlefield_384x320.y4m -c:v libx264 –x264opts aud=1 -threads 4 -b:v 500K -preset veryslow -g 60 -keyint_min 60 -sc_threshold 0 aud.h264
Encode x264 with ffmpeg
Example: encode 200 first frames, VBR Bitrate 15Mbps, number of slices 15 per frame, no B frame (IPPP stream), GOP size 60 frames, AUD added at the start of each frame:
ffmpeg -y -s 1920×1080 -i test.yuv -c:v libx264 -x264opts aud=1:bframes=0 -threads 4 -b:v 15M -preset veryfast -g 60 -keyint_min 60 -sc_threshold 0 -slices 15 -frames 200 aud.h264
Benchmark option of ffmpeg
the switch ‘-benchmark’ provides the following additional info:
maxrss serves to indicate the maximum RAM used during the ffmpeg execution
rtime the elapsed clock time (or the wall-clock time)
stime – system time taken from rtime
utime the sum of processing time across all threads. In parallel modes, utime exceeds rtime.
Example:
ffmpeg -benchmark -s 640x480 -i fifa_640x480.yuv -y -c:v libx264 -r 60 -g 60 -keyint_min 60 -b:v 4000k -maxrate 5000k -x264-params ref=1:bframes=0 fifa_640x480.h264
....
bench: utime=11.688s stime=0.281s rtime=2.143s
bench: maxrss=158168kB
....
from the results we can deduce that parallelization of x264 increases encoding time by ~5 times, (11.688-0.281)/2.143
Free H264 High Level Stream Analyzer
I compiled the free H264 High Level Stream Analyzer (it’s a headache) of Lei Xiaohua for Windows (Release/Win32). GUI version is located here.
The analyzer parses SPS, PPS and slice headers (therefore i call it “high-level”)
License:
H.264 ·ÖÎöÆ÷
H.264 Analysis
À×Ïöæè Lei Xiaohua
leixiaohua1020@126.com
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Communication University of China / Digital TV Technology
http://blog.csdn.net/leixiaohua1020
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H.264 Stream Analysis Tools
23+ years’ programming and theoretical experience in the computer science fields such as video compression, media streaming and artificial intelligence (co-author of several papers and patents).
the author is looking for new job, my resume
Related posts:
Parts of book “Anatomy of H.264/AVC”
How Cope with I-frame Bit-Rate Peaks
Frame_num is not frame counter (it is not incremented after a non-reference frame) – benefits and rationale
idr_pic_id and Redundant Pictures in H.264/AVC
Why Some Paremeters in SPS/PPS are Exp-Golomb-Coded?
Scalable Video Coding (SVC) of AVC/H.264
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