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Improve latency solution report and rework documentation
* Make the font size a bit smaller.
* Avoid taking zero delta values.
* Filter out anomaly peaks exceeding the average value by 25%
from the calculation of the average latency.
* Add file info to the diagram.
* Print results in console.
* Rework the latency measurement solution documentation.
Signed-off-by: Konstantin Ilichev <konstantin.ilichev@intel.com>
1. Build and install FFmpeg with the Media Communications Mesh FFmpeg plugin
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@@ -279,11 +275,6 @@ ffmpeg version n6.1.1-152-ge821e6c21d Copyright (c) 2000-2023 the FFmpeg develop
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built with gcc 11 (Ubuntu 11.4.0-1ubuntu1~22.04)
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```
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While measuring latency, it is necessary to configure FFmpeg with additional parameters. If the error `No such filter: 'drawtext'` occurs, please reconfigure and rebuild FFmpeg:
# End To End Latency Measurement — Media Communications Mesh
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# End-to-End Latency Measurement — Media Communications Mesh
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This document describes a simple solution for measuring end-to-end latency in Media Communications Mesh.
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## Overview
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The solution is based on the FFmpeg ability to print current timestamps on the sender side (Tx) and the receiver side (Rx), and the use of Optical Character Recognition (OCR) to read the timestamps out of each received video frame and calculate the delta. The choice of OCR is determined by the fact that the text can be effectively recognized even if the picture is affected by any sort of a lossy video compression algorithm somewhere in the transmission path in the Mesh. To achieve proper accuracy of the measurement, both Tx and Rx host machines should be synchronized using Precision Time Protocol (PTP).
1. Tx side – The user starts FFmpeg with special configuration to stream video via the Mesh.
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1. Rx side – The user starts FFmpeg with special configuration to receive the video stream from the Mesh.
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1. Tx side – FFmpeg prints the current timestamp as a huge text at the top of each video frame and transmits it via the Mesh.
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1. Rx side – FFmpeg prints the current timestamp as a huge text at the bottom of each video frame received from the Mesh and saves it on the disk.
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1. After transmission is done, there is a resulting MPEG video file on the disk on the Rx side.
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1. The user runs the solution script against the MPEG file that recognizes the Tx and Rx timestamps in each frame, and calculates the average latency based on the difference between the timestamps. Additionally, the script generates a latency diagram and stores it in JPEG format on the disk.
## Important notice on latency measurement results
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Before reading this document, please read [FFmpeg Plugin](FFmpegPlugin.md) to familiarize yourself with FFmpeg usage, as this document provides an extension.
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> Please note the calculated average latency is highly dependent on the hardware configuration and CPU background load, and cannot be treated as an absolute value. The provided solution can only be used for comparing the latency in different Mesh configurations and video streaming parameters, as well as latency stability checks.
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**Note:** Currently, latency measurement is available only for video transport.
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## Build and install steps
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1. Please follow build and install steps from [FFmpeg Plugin](FFmpegPlugin.md). with one exception, FFmpeg configuration tool requires additional parameters.
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> It is assumed that Media Communications Mesh is installed on the Tx and Rx host machines according to [Setup Guide](SetupGuid.md).
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If [FFmpeg Plugin](FFmpegPlugin.md) was installed earlier, remove its directory before proceeding with the following.
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1. Clone the FFmpeg 7.0 repository and apply patches.
> Make sure `network_interface_1` and `network_interface_2` are connected to the same network.
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*__host-1 Controller clock__
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```bash
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sudo ptp4l -i <network_interface_1> -m 2
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sudo phc2sys -a -r -r -m
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```
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## Example – Run video transmission between 2 FFmpeg instances on the same host
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* __host-2 Worker clock__
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```bash
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sudo ptp4l -i <network_interface_2> -m 2 -s
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sudo phc2sys -a -r
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```
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This example demonstrates sending a video file from the 1st FFmpeg instance to the 2nd FFmpeg instance via Media Communications Mesh on the same host, with timestamps to measure end-to-end latency using the `drawtext` feature in FFmpeg. The `drawtext` filter allows you to overlay timestamps directly onto the video stream, providing a visual representation of latency as the video is processed and transmitted between instances/hosts.
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## Example – Measuring transmission latency between two FFmpeg instances on the same host
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### Run Mesh Agent
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This example demonstrates sending a video file from the 1st FFmpeg instance to the 2nd FFmpeg instance via Media Communications Mesh on the same host, and then calculation of transmission latency from the recorded video.
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1. Run Mesh Agent
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```bash
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mesh-agent
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```
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###Run Media Proxy
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1. Run Media Proxy
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```bash
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sudo media_proxy \
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-t 8002
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```
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### Receiver side setup
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1. Start the Receiver side FFmpeg instance
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```bash
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sudo MCM_MEDIA_PROXY_PORT=8002 ffmpeg \
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-pixel_format yuv422p10le -
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```
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When sending a raw video file that lack metadata, you must explicitly provide FFmpeg
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with the necessary video frame details. This includes specifying the format
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`-f rawvideo`, pixel format `-pix_fmt`, and resolution `-s WxH`. Example:
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When sending a raw video file, e.g. of the YUV format, you have to explicitly specify the file format `-f rawvideo`, the pixel format `-pix_fmt`, and the video resolution `-s WxH`:
Please note that `-readrate` value have to be calculated based on `-frame_rate` parameter, simple equation is as follow:
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`readrate = frame_rate / 25`, for example:
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The `-readrate` value is calculated from the `-frame_rate` parameter value using the following equation: $readrate=framerate\div25$. Use the pre-calculated values from the table below.
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| frame_rate | readrate |
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|------------|-------------------|
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| 25 | 25 / 25 = 1 |
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| 50 | 50 / 25 = 2 |
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| 60 | 60 / 25 = 2.4 |
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1. Run the script against the recorded MPEG file. The first argument is the input video file path. The second argument is the optional latency diagram JPEG file path to be generated.
File: recv.mp4 | Last modified: 2025-06-02 13:49:54 UTC
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Resolution: 640x360 | FPS: 25.00
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Average End-to-End Latency: 564.61 ms
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```
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See the [Sample latency diagram](#sample-latency-diagram).
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## Example – Run video transmission between 2 FFmpeg instances on different hosts
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## Example – Measuring transmission latency between two FFmpeg instances on different hosts
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This example demonstrates sending a video file from the 1st FFmpeg instance to the 2nd FFmpeg instance via Media Communications Mesh, with timestamps to measure end-to-end latency using the `drawtext` feature in FFmpeg. The `drawtext` filter allows you to overlay timestamps directly onto the video stream, providing a visual representation of latency as the video is processed and transmitted between instances/hosts.
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This example demonstrates sending a video file from the 1st FFmpeg instance to the 2nd FFmpeg instance via Media Communications Mesh on the same host, and then calculation of transmission latency from the recorded video.
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###Run Mesh Agent
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1. Run Mesh Agent
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```bash
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mesh-agent
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```
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### Receiver side setup
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1. Start Media Proxy
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1. Start Media Proxy on the Receiver host machine
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```bash
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sudo media_proxy \
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-t 8002
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```
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1. Start FFmpeg to receive frames from Media Communications Mesh and save received data on hard drive
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1. Start the Receiver side FFmpeg instance
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```bash
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sudo MCM_MEDIA_PROXY_PORT=8002 ffmpeg \
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-pixel_format yuv422p10le -
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```
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## Stream postprocessing
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The generated stream can be analyzed manually, but it is a long process. To accelerate it, there is a small sript written in Python that automatically extracts and plots latency.
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1. Run the script against the recorded MPEG file. The first argument is the input video file path. The second argument is the optional latency diagram JPEG file path to be generated.
File: recv.mp4 | Last modified: 2025-06-02 13:49:54 UTC
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Resolution: 640x360 | FPS: 25.00
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Average End-to-End Latency: 564.61 ms
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```
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When preparing FFmpeg command if you change parameters of `drawtext` filter, especialy `fontsize`, `x`, `y` or `text`, you have to adjust script __text-detection.py__ too, please refer to function `extract_text_from_region(image, x, y, font_size, length)`
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See the [Sample latency diagram](#sample-latency-diagram).
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