FFMPEG Sources

When using ffmpeg, be sure to use the zerolatency option to get real-time output. This is not set automatically. Without the zerolatency setting the encoder will introduce 0.5 seconds of end-to-end latency out of the gate. Please refer to the ffmpeg documentation for details.

An example ffmpeg command to create test content is:

ffmpeg -re -f lavfi -i testsrc=size=1280x720:rate=30 -f lavfi -i aevalsrc="0.1*sin(2*PI*(360-2.5/2)*t) | 0.1*sin(2*PI*(360+2.5/2)*t)" -pix_fmt yuv420p -vcodec libx264 -profile:v baseline -deblock 1:0 -bitrate 500k -tune zerolatency -flags low_delay -fflags '+nobuffer+flush_packets' -max_delay 0 -muxdelay 0 -x264opts keyint=30 -acodec aac -ar 48000 -ac 2 -b:a 128k -f flv rtmp://ingest.phenixrts.com:80/ingest/96characterStreamKey;capabilities=hd,multi-bitrate,mpegts-unicast-ingest;tags=my-awesome-stream-id

Where 96characterStreamKey is the stream key to be used when publishing, which can be found in the Customer Portal under the Properties tab for a Channel or Room.

To measure latency, add a timestamp overlay:

ffmpeg -re -f lavfi -i testsrc=size=1280x720:rate=30 -f lavfi -i aevalsrc="0.1*sin(2*PI*(360-2.5/2)*t) | 0.1*sin(2*PI*(360+2.5/2)*t)" -pix_fmt yuv420p-vf "drawtext=text='timestamp: %{pts \: hms}': x=20: y=20: fontsize=72:fontcolor=white@0.9: box=1: boxcolor=black@0.6" -vcodec libx264 -profile:v baseline -deblock 1:0 -bitrate 500k -tune zerolatency -flags low_delay -fflags '+nobuffer+flush_packets' -max_delay 0 -muxdelay 0 -x264opts keyint=30 -acodec aac -ar 48000 -ac 2 -b:a 128k -f flv rtmp://ingest.phenixrts.com:80/ingest/96characterStreamKey;capabilities=hd,multi-bitrate,mpegts-unicast-ingest;tags=my-awesome-stream-id

Where 96characterStreamKey is the stream key to be used when publishing, which can be found in the Customer Portal under the Properties tab for a Channel or Room.

An example of the resulting video stream in the Portal's Details page is shown below.

FFmpeg commands may need to be optimized for real-time streaming at different levels depending on the use case:

• input protocol and device
• output protocol and device
• muxing / demuxing
• encoding

In general, when using FFMPEG with Phenix, always:

• Include these flags:
  • flags low_delay
  • fflags '+nobuffer+flush_packets'
• Encode for real-time: 1s GoP interval, or at least less than 2s.
• Enforce the lowest muxing and demuxing delays, as a result, packets at the end of the chain are better ordered for real-time, e.g., V V A V V V A V V A ... instead of V V V V V V V A A A V V V V V ... which reduces the playout delay. To do this, use:
  • max_delay 0
  • muxdelay 0

Depending on the input, reduce the probing overhead. e.g.,

• fpsprobesize 1
• analyzeduration 0

Apply optimization specific to the encoder. For example, optimizations and configurations differ between libx264 and h264_nvenc. Contact Phenix for details.

Additional optimizations depend on the input and output protocols. For example, when using an RTSP input, the arguments -reorder_queue_size 1 and -buffer_size 0 can be included.