This influences the quality of encoded video. Scaling list offers a mechanism to scale the transform coefficients by specifying scaling matrices. To enable temporal AQ, set the -temporal-aq option to 1 on the FFmpeg command line. Temporal AQ exploits this fact and redistributes more bits to static or low motion regions. The high motion regions are not very sensitive to the human eye as compared with low motion regions. It utilizes the lookahead frames to capture the temporal characteristics where static/low motion or background is differentiated with high motion regions. Temporal AQ adjusts the QP based on the temporal characteristics of the sequence. If no value is specified for the -spatial-aq-gain option, the default value is 50. To enable spatial AQ, set the -spatial-aq-gain to 1 and the -spatial-aq-gain to 50 on the FFmpeg command line. The range of this option is from 0 to 100 and indicates the strength of this algorithm as a percentage. The spatial AQ algorithm can be controlled using the -spatial-aq-gain option. It is recommended to turn this feature off when performing PSNR/VMAF based evaluation. Although spatial AQ improves video qualitity, it hurts objective metrics and causes a drop in PSNR and VMAF. This redistribution of bits to visually perceptible regions of the frame brings about visual improvement. Spatial AQ exploits this and provides more bits to the low texture and flat regions at the expense of high texture regions. The human eye is more sensitive to regions which are flat and have low texture than regions which have lots of detail and texture. Spatial AQ adjusts the QP within a frame based on the spatial characteristics. Both of these AQ modes are enabled by default, and -qp-mode is set to relative-load when -lookahead_depth >= 1. The Xilinx video encoders support two types of AQ: Spatial Adaptive Quantization and Temporal Adaptive Quantization. It exploits the fact that the human eye is more sensitive to certain regions of a frame and redistributes more bits to those regions. The QP for each frame is determined by the rate control, and adaptive quantization (AQ) adjusts QP on top of that for different regions within a frame. This tool improves the video qualitity by changing the quantization parameter (QP) within a frame. To enable lookahead, use the -lookahead_depth option on the FFmpeg command line. When latency is tolerable in applications, Xilinx recommends a lookahead depth of 20 frames to get optimum video quality. This redistribution results in better video quality. The rate control uses these measures to distribute more bits to frames which are hard to encode, and less bits to frames which are easy to encode. Spatial and temporal complexity measures are computed for these frames. Lookahead is used to improve the accuracy of rate control by enabling the encoder to buffer a specified number of frames (using the parameter). To change B frames, use the -bf option on the FFmpeg command line. bf 1 for all other content, including gaming and fast motion streams. bf 2 for static or slow moving scenes, talking heads, or video conferencing type of content Xilinx recommends the following B frames settings: Generally, more B-frames helps compression, but hurts very high motion scenes. The number of B frames can be adjusted according to the amount of motion in the video content. This provides the best tradeoffs for both video quality and objective quality use cases. The default number of B frames is 2, but for most streams, the optimal number of B frames is 1. Various examples illustrating the effect of these settings can be found here: Quality analysis examples. The sections below describe the major FFmpeg options impacting video quality. However, there are some encoder parameters which can be used to adjust the video quality. It is primarily a function of target bit rate and type of video content. The quality of encoded video depends on various factors. Setting this option to debug displays comprehensive debug information about the job Considerations for Decoding and Encoding 4K Streams.Using FFmpeg for Video Encoding and Decoding.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |