Basic Concepts

Key Terminology

Codec

A codec (coder/decoder) is an algorithm that compresses and decompresses audio or video data.

Category	Codecs
Video	H.264, H.265/HEVC, VP8, VP9, AV1, ProRes, DNxHD
Audio	AAC, MP3, Opus, FLAC, AC3, PCM

Container Format

A container holds encoded audio/video data along with metadata, subtitles, and chapter information.

Common containers: MP4, MKV, MOV, WebM, AVI, TS, MPEG

Bitrate

The amount of data per second. Higher bitrate = better quality = larger file.

• CBR (Constant Bitrate) — fixed rate throughout
• VBR (Variable Bitrate) — adapts quality to content complexity
• CRF (Constant Rate Factor) — quality-based encoding (FFmpeg-specific)

Frame Rate

The number of frames per second (fps). Common values: 24, 25, 30, 60.

Understanding FFmpeg Command Structure

The core rule: Options apply to the next specified input or output file.

ffmpeg [global_options] [input_options] -i input [output_options] output

ffmpeg -hide_banner          # global: suppress startup banner
     -y                      # global: overwrite output without asking
     -i input.mkv            # input file
     -c:v libx264            # output video codec
     -preset fast            # output video option
     -crf 22                 # output video option
     -c:a aac                # output audio codec
     -b:a 192k               # output audio option
     output.mp4              # output file

Stream Selection

FFmpeg processes streams (video, audio, subtitle tracks) independently.

# Copy video stream, transcode audio
ffmpeg -i input.mkv -c:v copy -c:a aac output.mp4

# Extract only the first video stream
ffmpeg -i input.mkv -map 0:v:0 -c copy output.mp4

# Extract video + audio track 2
ffmpeg -i input.mkv -map 0:v:0 -map 0:a:1 -c copy output.mkv

Two-Pass Encoding

For the best quality at a target bitrate, use two passes:

# Pass 1: analyze
ffmpeg -i input.mp4 -c:v libx264 -preset slow -bitrate 5M \
  -pass 1 -f rawvideo -y /dev/null

# Pass 2: encode
ffmpeg -i input.mp4 -c:v libx264 -preset slow -bitrate 5M \
  -pass 2 output.mp4

Key Concepts Summary

Concept	Description
Codec	Compression/decompression algorithm
Container	File format holding streams + metadata
Bitrate	Data rate (quality vs. file size)
FPS	Frames per second
CRF	FFmpeg quality-based encoding (0=lossless, 23=default, 51=worst)
Preset	Encoding speed vs. compression tradeoff (ultrafast → veryslow)
Filter	Audio/video transformation applied during encoding
Stream	Individual video/audio/subtitle track in a container