What are the common FFmpeg issues? How to solve encoding, format, and performance problems? - 面试题

When using FFmpeg for audio/video processing, you often encounter various problems. This article summarizes common issues and their solutions.

Encoding Issues

Video Encoding Failed

Problem: "Error while opening encoder" error during encoding

Solution:

bash
# Check if encoder is available
ffmpeg -encoders | grep h264

# Use different encoder
ffmpeg -i input.mp4 -c:v libx264 output.mp4
ffmpeg -i input.mp4 -c:v h264_nvenc output.mp4

Encoding Too Slow

Problem: Encoding speed is much lower than real-time speed

Solution:

bash
# Use faster preset
ffmpeg -i input.mp4 -c:v libx264 -preset ultrafast output.mp4

# Use hardware acceleration
ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc output.mp4

# Lower encoding quality
ffmpeg -i input.mp4 -c:v libx264 -crf 28 output.mp4

Audio/Video Out of Sync

Problem: Audio and video are out of sync in output video

Solution:

bash
# Use -async parameter to sync audio
ffmpeg -i input.mp4 -async 1 output.mp4

# Re-encode audio and video
ffmpeg -i input.mp4 -c:v libx264 -c:a aac output.mp4

# Specify frame rate
ffmpeg -i input.mp4 -r 25 output.mp4

Format Issues

Unsupported Format

Problem: "Unsupported codec" error

Solution:

bash
# View supported formats
ffmpeg -formats

# Convert to supported format
ffmpeg -i input.mkv -c:v libx264 -c:a aac output.mp4

# Use -c copy to copy streams
ffmpeg -i input.mp4 -c copy output.mkv

Container Format Incompatible

Problem: Some players cannot play output file

Solution:

bash
# Use standard container format
ffmpeg -i input.mp4 -c:v libx264 -c:a aac -movflags +faststart output.mp4

# Generate more compatible MP4
ffmpeg -i input.mp4 -c:v libx264 -profile:v baseline -level 3.0 output.mp4

Performance Issues

High CPU Usage

Problem: CPU usage reaches 100% during encoding

Solution:

bash
# Limit thread count
ffmpeg -i input.mp4 -threads 4 -c:v libx264 output.mp4

# Use hardware acceleration
ffmpeg -hwaccel cuda -i input.mp4 -c:v h264_nvenc output.mp4

# Lower encoding complexity
ffmpeg -i input.mp4 -c:v libx264 -preset ultrafast -tune fastdecode output.mp4

High Memory Usage

Problem: High memory usage when processing large files

Solution:

bash
# Use streaming processing
ffmpeg -i input.mp4 -c:v libx264 -f null -

# Reduce buffer size
ffmpeg -i input.mp4 -c:v libx264 -bufsize 1M output.mp4

# Segment processing
ffmpeg -i input.mp4 -c copy -f segment -segment_time 300 segment_%03d.mp4

Streaming Issues

RTMP Push Failed

Problem: Failed to push to RTMP server

Solution:

bash
# Check network connection
ping rtmp.server.com

# Use correct push URL
ffmpeg -re -i input.mp4 -c copy -f flv rtmp://server/live/stream_key

# Add timeout parameter
ffmpeg -re -i input.mp4 -timeout 5000000 -c copy -f flv rtmp://server/live/stream_key

HLS Playback Stuttering

Problem: HLS stream stutters during playback

Solution:

bash
# Increase segment duration
ffmpeg -i input.mp4 -f hls -hls_time 10 output.m3u8

# Reduce segment count
ffmpeg -i input.mp4 -f hls -hls_list_size 5 output.m3u8

# Use shorter GOP
ffmpeg -i input.mp4 -c:v libx264 -g 25 -f hls output.m3u8

Filter Issues

Filter Chain Error

Problem: "Invalid filterchain" error when using filter

Solution:

bash
# Check filter syntax
ffmpeg -i input.mp4 -vf "scale=1280:720" output.mp4

# Use -filter_complex for complex filters
ffmpeg -i input.mp4 -filter_complex "[0:v]scale=1280:720[v]" -map "[v]" output.mp4

# Step-by-step processing
ffmpeg -i input.mp4 -vf "scale=1280:720" -vf "crop=640:360" output.mp4

Filter Performance Issue

Problem: Processing speed slows down after using filter

Solution:

bash
# Use hardware accelerated filter
ffmpeg -hwaccel cuda -i input.mp4 -vf "scale_npp=1280:720" output.mp4

# Optimize filter order
ffmpeg -i input.mp4 -vf "crop=640:480,scale=320:240" output.mp4

# Reduce complex filters
ffmpeg -i input.mp4 -vf "scale=1280:720" output.mp4

Debugging Tips

View Detailed Information

bash
# Show verbose logs
ffmpeg -v verbose -i input.mp4 output.mp4

# Show debug information
ffmpeg -v debug -i input.mp4 output.mp4

# Analyze input file
ffmpeg -i input.mp4 -f null -

Performance Analysis

bash
# Show processing time
ffmpeg -i input.mp4 -c:v libx264 -stats output.mp4

# Benchmark
ffmpeg -benchmark -i input.mp4 -c:v libx264 -f null -

# Show encoding statistics
ffmpeg -i input.mp4 -c:v libx264 -pass 1 -f null /dev/null

Best Practices

Use correct encoding parameters: Choose appropriate encoders and parameters based on target platform
Monitor resource usage: Use system monitoring tools to observe CPU, memory, and GPU usage
Test small samples: Test small samples before processing large files
Use hardware acceleration: Prioritize hardware encoding/decoding when supported
Set reasonable thread count: Set appropriate thread count based on CPU cores

When encountering problems, first check the error message, then choose the appropriate solution based on the error type. If the problem persists, you can check the FFmpeg documentation or seek help from the community.