Error Starting Encoding with Multiple Video Streams in FFmpeg

Error Starting Encoding Multiple Video Streams with FFmpeg

FFmpeg is a powerful, open-source tool used for handling multimedia files, including audio, video, and images. It is widely used for transcoding, streaming, and manipulating various formats. However, when trying to encode multiple video streams using FFmpeg, you might encounter errors. This article will discuss the issue and provide solutions.

Understanding the FFmpeg Command

The following FFmpeg command is used to transcode a video file with multiple video streams:

Here's a breakdown of the command:

• -i /2160.mp4: specifies the input file
• -c:libopus -b:128k -ar48000: sets the audio codec to Opus, bitrate to 128 kbps, and audio sample rate to 48000 Hz
• -c:vlibvpx-vp9 -pix_fmt yuv420p -g240: sets the video codec to VP9, pixel format to yuv420p, and GOP size to 240
• -map v:0 -vf "scale=-2:144": maps the first video stream and scales it to a height of 144 pixels
• -map v:1 -vf "scale=-2:144": maps the second video stream and scales it to a height of 144 pixels
• output.webm: specifies the output file

Error Starting Encoding Multiple Video Streams

When trying to encode multiple video streams using the aforementioned FFmpeg command, you might encounter an error similar to:

This error occurs because FFmpeg does not support using multiple -vf options for the same stream. To resolve this issue, you need to use the filter\_complex filtergraph instead.

Using filter\_complex

To fix the error, you can modify the FFmpeg command as follows:

Here's what changed:

• filter\_complex "[0:v:0]scale=-2:144[v0]; [0:v:1]scale=-2:144[v1]": uses the filter\_complex to scale both video streams
• -map "[v0]" -map "[v1]": maps the scaled video streams to the output

When trying to encode multiple video streams using FFmpeg, you might encounter errors if you use multiple -vf options for the same stream. To resolve this issue, you can use the filter\_complex filtergraph instead. The filter\_complex filtergraph allows you to apply multiple filters to the same stream, making it possible to encode multiple video streams without encountering errors.

References

• FFmpeg Documentation
• Scaling within FFmpeg
• FFmpeg: Multiple -vf for the same stream