transcode

Convert videos between formats, codecs, and containers for universal compatibility.

Overview

The transcode command converts videos from one format/codec to another, ensuring compatibility across platforms, devices, and use cases. Whether you're converting old AVI files to modern MP4, preparing videos for web delivery, or migrating to more efficient codecs, transcode handles it intelligently.

Key Features:

• 🔄 Format conversion (MP4, WebM, MKV, AVI)
• 🎬 Codec migration (H.264, H.265, VP9, AV1)
• 📦 Container remuxing (fast, lossless)
• 🌐 Platform-optimized presets
• 📁 Batch folder processing
• ⚡ Smart codec defaults per format

Common Use Cases:

• Converting legacy formats (AVI, WMV) to modern MP4
• Preparing videos for web (MP4 with H.264)
• Creating HTML5-compatible WebM files
• Migrating to efficient codecs (H.265, AV1)
• Fixing incompatible video formats
• Container changes without re-encoding

Usage

Options

Flag Details

--format - Output Format

Specify the output container format.

Available Formats:

MP4 (.mp4) - Universal

• Compatibility: All devices, browsers, platforms
• Best Codecs: H.264, H.265 (HEVC)
• Audio: AAC, MP3
• Use When: Maximum compatibility needed
• Best For: General distribution, mobile devices, web, social media

WebM (.webm) - Open Web Standard

• Compatibility: All modern browsers, limited device support
• Best Codecs: VP9, VP8, AV1
• Audio: Opus, Vorbis
• Use When: HTML5 video, YouTube, open-source projects
• Best For: Web streaming, progressive web apps

MKV (.mkv) - Matroska

• Compatibility: Desktop players, advanced features
• Best Codecs: Any codec (highly flexible)
• Audio: Multiple audio tracks, subtitles
• Use When: Need advanced features (chapters, multiple tracks)
• Best For: High-quality archival, media centers, anime

AVI (.avi) - Legacy Format

• Compatibility: Universal, older systems
• Best Codecs: H.264, MPEG-4, DivX
• Audio: MP3, PCM
• Use When: Legacy system compatibility
• Best For: Older editing software, retro compatibility

Learn More:

• Container Format Comparison

--codec - Video Codec

Select the video encoding codec.

H.264 (AVC) - Universal Standard

• Compatibility: ✅✅✅ All devices
• Encoding Speed: Fast
• Compression: Good
• File Size: Baseline reference
• Use When: Need maximum compatibility
• Patent Status: Free for end users

H.265 (HEVC) - High Efficiency

• Compatibility: Modern devices (2016+)
• Encoding Speed: Slow (2-3x longer)
• Compression: Excellent (40-50% smaller than H.264)
• File Size: Much smaller
• Use When: 4K video, storage critical, modern distribution
• Patent Status: Licensing complexities

VP9 - Google's Open Codec

• Compatibility: Web browsers, YouTube
• Encoding Speed: Very slow
• Compression: Excellent (similar to H.265)
• File Size: Small
• Use When: WebM format, open-source requirements
• Patent Status: Royalty-free

AV1 - Next Generation

• Compatibility: Latest browsers/devices (2020+)
• Encoding Speed: Extremely slow
• Compression: Best (20-30% better than H.265)
• File Size: Smallest
• Use When: Future-proofing, streaming platforms
• Patent Status: Open, royalty-free

Auto-Selection: If not specified, codec is chosen based on output format:

• MP4 → H.264
• WebM → VP9
• MKV → H.264
• AVI → H.264

Learn More:

• Video Codec Guide
• H.264 vs H.265 vs VP9

--audio-codec - Audio Codec

Select the audio encoding codec.

AAC - Advanced Audio Coding

• Compatibility: Universal
• Quality: Excellent
• File Size: Efficient
• Best For: MP4 videos, general use
• Bitrate: 128k standard, 192k high quality

MP3 - MPEG Audio Layer 3

• Compatibility: Universal (older than AAC)
• Quality: Good
• File Size: Moderate
• Best For: Legacy compatibility, AVI format
• Bitrate: 128k standard, 192k high quality

Opus - Modern Open Codec

• Compatibility: Modern browsers, WebM
• Quality: Best (better than AAC at lower bitrates)
• File Size: Very efficient
• Best For: WebM videos, streaming
• Bitrate: 96k excellent, 128k transparent

Auto-Selection:

• MP4/MKV → AAC
• WebM → Opus
• AVI → MP3

--bitrate - Video Bitrate

Set target video bitrate (alternative to CRF-based quality).

Format: Number + unit

• k = kilobits per second (e.g., 2000k = 2 Mbps)
• M = megabits per second (e.g., 5M = 5 Mbps)

Recommended Bitrates:

CRF vs Bitrate:

• CRF: Better quality distribution, variable file size
• Bitrate: Predictable file size, may waste bits on simple scenes

--crf - Constant Rate Factor

Control encoding quality (used when bitrate not specified).

Range: 0-51, lower = better quality

• 15-18 - Near-lossless (large files)
• 19-23 - High quality ← 23 is default
• 24-28 - Good quality (smaller files)
• 29+ - Lower quality (compression artifacts)

Codec-Specific Recommendations:

• H.264: CRF 18-23 (23 default)
• H.265: CRF 22-28 (can go higher due to better compression)
• VP9: CRF 23-31
• AV1: CRF 20-30

--audio-bitrate - Audio Bitrate

Set audio quality/bitrate.

Common Values:

• 96k - Acceptable for speech
• 128k - Standard quality ← default
• 192k - High quality for music
• 256k - Professional quality
• 320k - Maximum quality

Impact on File Size: Audio typically 5-10% of total file size at standard settings.

Format Support

MP4 (.mp4)

• Compatibility: Universal (all devices)
• Best codecs: H.264, H.265
• Audio: AAC, MP3
• Use case: General distribution, web, mobile

WebM (.webm)

• Compatibility: Modern web browsers
• Best codecs: VP9, VP8
• Audio: Opus, Vorbis
• Use case: HTML5 video, web streaming

MKV (.mkv)

• Compatibility: Desktop players, advanced users
• Best codecs: Any (highly flexible)
• Audio: Multiple tracks supported
• Use case: High-quality archival, multiple audio/subtitle tracks

AVI (.avi)

• Compatibility: Legacy systems, wide software support
• Best codecs: H.264, MPEG-4
• Audio: MP3, AAC
• Use case: Legacy compatibility, older editing software

Codec Mapping

The plugin automatically selects appropriate codecs for each format:

Examples

Basic Format Conversion

Specify Output Location

Codec Selection

Audio Codec Control

Bitrate Control

CRF-Based Quality

# Use CRF for quality-based encoding (recommended)
mediaproc video transcode input.avi -f mp4 --crf 23

# High quality
mediaproc video transcode input.avi -f mp4 --crf 18

# Smaller file size
mediaproc video transcode input.avi -f mp4 --crf 28

HTML5 Web Video

# Create WebM for modern browsers
mediaproc video transcode video.mp4 -f webm -c vp9 --audio-codec opus

# Create MP4 fallback for older browsers
mediaproc video transcode video.mp4 -f mp4 -c h264 --audio-codec aac

# Use in HTML:
# <video>
#   <source src="video.webm" type="video/webm">
#   <source src="video.mp4" type="video/mp4">
# </video>

Codec Upgrade

# Upgrade old H.264 to H.265 for better compression
mediaproc video transcode old-video.mp4 -c h265 -o new-video.mp4

# Upgrade to VP9 for web
mediaproc video transcode video.mp4 -c vp9 -f webm --crf 20

Dry Run Preview

# Preview transcoding command
mediaproc video transcode input.avi -f mp4 --dry-run

Output:

Batch Transcoding

# Create WebM versions of all MP4 files
for file in *.mp4; do
  mediaproc video transcode "$file" -f webm -o webm/
done

# Batch convert with specific codec
for file in *.mov; do
  mediaproc video transcode "$file" -f mp4 -c h265 -o h265/
done

Folder Processing

# Convert entire folder to WebM
mediaproc video transcode videos/ -f webm -c vp9 -o output/

# Batch convert with quality control
mediaproc video transcode source/ -f mp4 -c h265 --crf 20 -o output/

Use Cases

Legacy Format Migration

Convert old video formats to modern standards:

# AVI to MP4
mediaproc video transcode old-videos/*.avi -f mp4 -o mp4/

# MOV to MP4
mediaproc video transcode *.mov -f mp4

# FLV to MP4
mediaproc video transcode flash-video.flv -f mp4

Web Platform Optimization

Create optimized videos for web delivery:

# YouTube (MP4 with H.264)
mediaproc video transcode video.avi -f mp4 -c h264 --crf 18

# Vimeo (MP4 or WebM)
mediaproc video transcode video.avi -f mp4 --bitrate 5M

# Self-hosted website (WebM + MP4 fallback)
mediaproc video transcode video.avi -f webm -c vp9 -o video.webm
mediaproc video transcode video.avi -f mp4 -c h264 -o video.mp4

Device Compatibility

Ensure playback on specific devices:

# Apple devices (MP4 with H.264)
mediaproc video transcode video.mkv -f mp4 -c h264 --audio-codec aac

# Android devices (MP4)
mediaproc video transcode video.avi -f mp4 -c h264

# Smart TVs (MP4, lower bitrate)
mediaproc video transcode 4k-video.mp4 --bitrate 8M -o tv-compatible.mp4

Streaming Preparation

Prepare videos for streaming services:

# High-quality stream
mediaproc video transcode source.avi -f mp4 --bitrate 5M --audio-bitrate 192k

# Medium-quality stream
mediaproc video transcode source.avi -f mp4 --bitrate 2M --audio-bitrate 128k

# Low-quality stream
mediaproc video transcode source.avi -f mp4 --bitrate 1M --audio-bitrate 96k

Archive Conversion

Convert to efficient archival formats:

# H.265 in MKV for space-efficient archival
mediaproc video transcode video.avi -f mkv -c h265 --crf 20

# VP9 in WebM
mediaproc video transcode video.mp4 -f webm -c vp9 --crf 20

Social Media Formatting

# Instagram (MP4 with AAC)
mediaproc video transcode video.avi -f mp4 -c h264 --audio-codec aac

# Twitter (MP4, specific bitrate)
mediaproc video transcode video.avi -f mp4 --bitrate 2M

# Facebook (MP4 H.264)
mediaproc video transcode video.avi -f mp4 -c h264 --crf 23

Technical Details

Container vs Codec

Container (format): The file wrapper that holds video/audio streams

• MP4, WebM, MKV, AVI

Codec: The algorithm that compresses video/audio data

• H.264, H.265, VP9, AAC, Opus

Example: MP4 container can hold H.264 or H.265 video + AAC audio

Transcoding vs Remuxing

Transcoding: Re-encode video (slow, quality loss)

# Changes codec, re-encodes video
mediaproc video transcode input.avi -f mp4 -c h264

Remuxing: Change container without re-encoding (fast, lossless)

# FFmpeg direct command for remuxing:
ffmpeg -i input.mkv -c copy output.mp4

The plugin always transcodes to ensure compatibility.

Codec Selection Logic

When codec is not specified, automatic selection:

1. MP4 format: H.264 video + AAC audio
2. WebM format: VP9 video + Opus audio
3. MKV format: H.264 video + AAC audio
4. AVI format: H.264 video + MP3 audio

Quality Control

CRF mode (default):

• Quality-based encoding
• Variable bitrate
• Consistent quality
• Recommended for most use cases

Bitrate mode:

• Target specific size
• Constant or average bitrate
• Predictable file sizes
• Use for streaming constraints

Performance Considerations

Encoding Speed

Relative encoding speeds (H.264 baseline = 1x):

• H.264: 1x (fast)
• H.265: 2-3x slower
• VP9: 3-5x slower
• AV1: 10-20x slower (not recommended for bulk processing)

When to Use Each Codec

H.264 (libx264):

• ✅ Universal compatibility needed
• ✅ Fast encoding required
• ✅ Live streaming
• ❌ Not ideal for 4K or UHD

H.265 (libx265):

• ✅ 4K/UHD content
• ✅ Storage space critical
• ✅ Modern devices (2016+)
• ❌ Slow encoding
• ❌ Limited older device support

VP9 (libvpx-vp9):

• ✅ Web delivery
• ✅ Open-source requirement
• ✅ YouTube compatibility
• ❌ Very slow encoding
• ❌ Limited hardware acceleration

AV1 (libaom-av1):

• ✅ Best compression (30% better than H.265)
• ✅ Future-proof
• ❌ Extremely slow (10-20x slower than H.264)
• ❌ Limited device support currently

Error Handling

Common Errors

FFmpeg not found:

Unsupported codec:

Invalid format:

Incompatible codec/format combination:

Best Practices

1. Choose the right format: MP4 for compatibility, WebM for web
2. Use CRF for quality: Better than fixed bitrate for most cases
3. Test codec support: Verify target devices support chosen codec
4. Keep source files: Never overwrite originals
5. Use dry-run: Preview commands before batch processing
6. Consider encoding time: H.264 is much faster than H.265/VP9
7. Match audio codec: AAC for MP4, Opus for WebM
8. Verify output: Always test transcoded videos play correctly

Troubleshooting

Output File Won't Play

• Check device/player codec support
• Try H.264 (most compatible): -c h264
• Use standard container: -f mp4
• Verify with: ffprobe output.mp4

Poor Quality Output

• Increase CRF (lower number): --crf 18
• Use higher bitrate: --bitrate 5M
• Choose better codec: -c h265
• Check source quality (can't improve bad source)

Encoding Too Slow

• Use H.264 instead of H.265/VP9: -c h264
• Reduce resolution first: mediaproc video resize input.mp4 --scale 1080p
• Use hardware acceleration (FFmpeg directly)
• Process fewer files in parallel

File Size Too Large

• Lower CRF: --crf 28
• Use efficient codec: -c h265
• Reduce bitrate: --bitrate 2M
• Compress after transcoding: mediaproc video compress output.mp4

Audio Sync Issues

• Check source file for issues
• Use verbose mode: -v
• Try different audio codec: --audio-codec aac
• Report FFmpeg errors from verbose output

Advanced Examples

Multi-Format Web Delivery

#!/bin/bash
# Create multiple formats for HTML5 video

input="source.avi"
output_name="video"

# WebM for modern browsers
mediaproc video transcode "$input" -f webm -c vp9 --crf 20 -o "${output_name}.webm"

# MP4 for older browsers
mediaproc video transcode "$input" -f mp4 -c h264 --crf 23 -o "${output_name}.mp4"

echo "Use in HTML:"
echo '<video controls>'
echo "  <source src=\"${output_name}.webm\" type=\"video/webm\">"
echo "  <source src=\"${output_name}.mp4\" type=\"video/mp4\">"
echo '</video>'

Adaptive Bitrate Ladder

#!/bin/bash
# Create multiple quality levels for adaptive streaming

input="source.mp4"

# 1080p high quality
mediaproc video transcode "$input" --bitrate 5M -o "1080p.mp4"

# 720p medium quality
mediaproc video transcode "$input" --bitrate 2.5M -o "720p.mp4"

# 480p low quality
mediaproc video transcode "$input" --bitrate 1M -o "480p.mp4"

Codec Comparison Test

#!/bin/bash
# Compare output of different codecs

input="test-video.mp4"

# H.264
mediaproc video transcode "$input" -c h264 --crf 23 -o "test-h264.mp4"

# H.265
mediaproc video transcode "$input" -c h265 --crf 23 -o "test-h265.mp4"

# VP9
mediaproc video transcode "$input" -c vp9 --crf 23 -o "test-vp9.webm"

# Compare sizes
ls -lh test-*.{mp4,webm}

Archive Conversion Pipeline

#!/bin/bash
# Convert old format archive to efficient modern format

for file in archive/*.{avi,mov,flv}; do
  filename=$(basename "$file")
  name="${filename%.*}"

  echo "Converting: $filename"
  mediaproc video transcode "$file" \
    -f mkv \
    -c h265 \
    --crf 20 \
    -o "converted/$name.mkv" \
    -v

  # Log file sizes
  original_size=$(du -h "$file" | cut -f1)
  new_size=$(du -h "converted/$name.mkv" | cut -f1)
  echo "$filename: $original_size -> $new_size" >> conversion_log.txt
done

Related Commands

• compress - Reduce file size after transcoding
• resize - Change resolution during transcoding
• extract-audio - Extract audio in different formats

See Also

• FFmpeg Formats Documentation
• FFmpeg Codecs
• HTML5 Video Browser Support
• Video Codec Comparison