Reduce Latency with FFplay for HDMI Encoders | Exvist Support

FAQs: Reduce Latency with FFplay for Encoder

Step-by-Step Guide to Reduce Latency with FFplay

1. Install FFmpeg and FFplay

Ensure that FFmpeg (which includes FFplay) is installed on your system. You can check if it's installed by running:
  1. ffplay -version
If it is not installed, you can download and install FFmpeg from the official site or use a package manager like apt or brew based on your operating system.

2. Open FFplay with RTSP Stream

Start by running FFplay with your RTSP stream URL:
  1. ffplay rtsp://192.168.1.120:554/live/1_0
Replace rtsp://192.168.1.120:554/live/1_0 with the actual RTSP URL of your video encoder.

3. Adjust Buffer Size

Reduce the default buffer size to minimize delay. Use the -rtsp_transport flag to select the transport protocol (TCP or UDP). UDP typically results in lower latency.
Example command:
  1. ffplay -rtsp_transport udp -fflags nobuffer -analyzeduration 0 -probesize 32 rtsp://192.168.1.120:554/live/1_0
Explanation:
  1. -rtsp_transport udp: Forces UDP transport, which is generally lower latency than TCP.
  2. -fflags nobuffer: Disables buffering to reduce latency.
  3. -analyzeduration 0: Limits the time FFplay spends analyzing the stream, helping to start playback quicker.
  4. -probesize 32: Limits the amount of data used to probe the stream, which also reduces latency.

4. Adjust Video Output Delay

Use the -sync flag to adjust video synchronization. Setting it to video forces FFplay to sync with the video stream, which can help with reducing latency.
Example command:
  1. ffplay -rtsp_transport udp -fflags nobuffer -analyzeduration 0 -probesize 32 -sync video rtsp://192.168.1.120:554/live/1_0

5. Reduce Video and Audio Buffering

Disable or minimize audio playback with -vn (no video) or adjust audio buffer sizes using -an (no audio) if audio is not necessary for the test.
Example:
  1. ffplay -rtsp_transport udp -fflags nobuffer -analyzeduration 0 -probesize 32 -sync video -an rtsp://192.168.1.120:554/live/1_0

6. Fine-tune Decoding Options

Add options to optimize decoding performance and minimize latency. For instance:
  1. ffplay -rtsp_transport udp -fflags nobuffer -analyzeduration 0 -probesize 32 -sync video -an -flags low_delay rtsp://192.168.1.120:554/live/1_0

7. Additional Optimizations (Optional)

You can further tune FFplay by using -x and -y flags to specify the size of the video window, and -framedrop to discard frames if they can't be processed quickly enough:
  1. ffplay -rtsp_transport udp -fflags nobuffer -analyzeduration 0 -probesize 32 -sync video -an -framedrop -flags low_delay -x 640 -y 360 rtsp://192.168.1.120:554/live/1_0
Explanation:
  1. -framedrop: Drops frames when the system can't keep up with decoding, reducing buffering.
  2. -x 640 -y 360: Specifies the resolution to play the video, reducing the decoding workload.

Final Command Example

  1. ffplay -rtsp_transport udp -fflags nobuffer -analyzeduration 0 -probesize 32 -sync video -an -framedrop -flags low_delay -x 640 -y 360 rtsp://192.168.1.120:554/live/1_0

8. Monitor Latency

After setting up, monitor the playback to observe the reduction in latency. You can use tools like FFprobe to measure latency in real-time by inspecting stream details.
Example FFprobe command to check the stream’s stats:
  1. ffprobe -v quiet -print_format json -show_streams rtsp://192.168.1.120:554/live/1_0
By using the above commands and tweaking the various flags, you can effectively reduce the latency when testing the RTSP stream from your video encoder.

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