Ffmpeg Playback

Ffmpeg Playback

Context: $ARGUMENTS

Quick start

• Preview a file: Step 1 — ffplay in.mp4
• Test a -vf filter live without transcoding: Step 2
• Debug pixel format / SAR / frame info: Step 3
• Visualize audio (waveform / spectrum / loudness meter): Step 4
• Fix AV-sync drift: Step 3 (-sync ext) + -vf setpts=PTS-STARTPTS
• Headless preview (no GUI): add -nodisp -autoexit (audio only)

When to use

• User wants to eyeball a clip after a cut, filter, or encode (QA pass).
• User is iterating on a -vf or -af chain and wants live feedback before running a full transcode.
• User needs visual AV diagnostics: waveform, spectrum, vectorscope, ebur128 loudness meter, or verbose logs to see pixel format / color range / SAR.
• User is debugging A/V drift, out-of-order PTS, or choppy playback.

Do NOT use for: long-term rendering (use ffmpeg-transcode), authoring filter chains to a file (use ffmpeg-video-filter / ffmpeg-audio-filter), inspecting metadata only (use ffmpeg-probe). ffplay is an interactive debug player — not a production media player.

Step 1 — Simple preview

ffplay in.mp4                          # play, loop off, window auto-sized
ffplay -ss 60 -t 10 in.mp4             # start at 60s, play 10s then quit (with -autoexit)
ffplay -autoexit in.mp4                # quit at EOF instead of hanging on last frame
ffplay -loop 0 in.mp4                  # infinite loop
ffplay -x 1280 -y 720 in.mp4           # force window size
ffplay -an in.mp4                      # mute / disable audio decoder
ffplay -vn in.mp4                      # audio only
ffplay -nodisp -autoexit in.mp4        # no window (audio plays; video decoded but not shown)

-ss is ffplay's start-offset seek — it only accepts a single timestamp and goes before the input file on the command line. There is no "output-side" seek in ffplay.

Step 2 — Filter-graph test (live, no transcode)

Use ffplay to preview a filter you'll later apply with ffmpeg. No file is written.

# Test a video filter chain
ffplay -vf "scale=1280:-2,eq=brightness=0.1,unsharp=5:5:1.0" in.mp4

# Test an audio filter chain
ffplay -af "loudnorm=I=-16:LRA=11:TP=-1.5" in.mp4

# Both at once
ffplay -vf "hqdn3d" -af "highpass=f=80" in.mp4

Press w during playback to cycle through / disable the video filter chain — useful for A/B comparison.

For complex graphs with multiple inputs, use -f lavfi with a source filter (movie=, amovie=) in a filtergraph:

ffplay -f lavfi "movie=in.mp4,split[a][b];[b]vflip[c];[a][c]hstack[out]"

When -f lavfi is used, the graph MUST terminate with labeled outputs. For combined audio+video use two sinks named [out0] (video) and [out1] (audio).

Step 3 — Debug mode: stats, pixel format, AV-sync

# In-window HUD: frame #, fps, VQ size, dropped frames (on by default in newer builds)
ffplay -stats in.mp4

# Verbose terminal log: shows pix_fmt, color_range, SAR/DAR, timebase, decoder
ffplay -loglevel verbose in.mp4

# Cycle stream with keyboard: a (audio), v (video), t (subtitle), c (chapter)

AV-sync debugging. ffplay picks audio as the master clock by default. Swap masters to narrow down drift:

ffplay -sync audio in.mp4    # default — video resyncs to audio
ffplay -sync video in.mp4    # audio resyncs to video (exposes dropped video frames as audio drift)
ffplay -sync ext   in.mp4    # both sync to an external wall clock — exposes stream-level drift

If you see monotonic drift, the fix is usually in a filter: prepend setpts=PTS-STARTPTS (video) and asetpts=PTS-STARTPTS (audio) to reset timestamps, or aresample=async=1 to soft-fix audio gaps.

Useful debug flags:

• -framedrop — drop video frames if CPU can't keep up (on by default when sync source is not video).
• -infbuf — unlimited demux buffer (for live/RTSP/slow sources).
• -vf "showinfo" — log per-frame metadata (pts, pkt_pos, mean).

Step 4 — Visualize audio

ffplay can render audio as video via lavfi source filters (amovie=). The graph must end in [out0] (video) + [out1] (audio).

# Waveform (overlay mode "cline") next to audio
ffplay -f lavfi "amovie=in.mp3,asplit[a][w];[w]showwaves=s=1280x120:mode=cline[v];[a][v]concat=n=1:v=1:a=1[out0][out1]"

# Spectrum
ffplay -f lavfi "amovie=in.mp3,showspectrum=s=1024x512:mode=combined:slide=scroll"

# Live loudness meter (EBU R128, 18 LU scale)
ffplay -f lavfi "amovie=in.mp3,ebur128=video=1:meter=18[out0][out1]"

# Vectorscope overlay on a video (live)
ffplay -vf "split[a][b];[b]vectorscope=mode=color3[c];[a][c]overlay=W-w" in.mp4

# Histogram + waveform monitor on a live video
ffplay -vf "split[a][b];[b]histogram[c];[a][c]hstack" in.mp4

Piped playback

ffplay reads stdin when the input is -:

ffmpeg -i in.mkv -c copy -f matroska - | ffplay -i -
ffmpeg -f lavfi -i testsrc=size=640x360:rate=30 -f mpegts - | ffplay -i -

Gotchas

• ffplay is a DEBUG player. There is no playlist, no UI for codec selection, no per-device audio routing. Do not ship it to end users.
• SDL2 is required. In headless SSH you get Could not initialize SDL - No available video device. Fix: X-forward (ssh -Y), VNC, or add -nodisp for audio only. SDL_VIDEODRIVER=dummy lets ffplay start without a window but you also won't see any video — use -nodisp instead.
• macOS opens its own window (Cocoa). No menu bar — keyboard shortcuts only work when the ffplay window has focus. Click it first.
• Audio device isn't selectable via ffplay flags. Use SDL env vars: SDL_AUDIODRIVER=coreaudio (mac) / alsa / pulse / dsp. To pick a specific device set AUDIODEV (OSS/ALSA) or configure PulseAudio default sink.
• -f lavfi graphs MUST end in labeled outputs. For video+audio that's [out0] and [out1] — BOTH are required when using ebur128=video=1 or showwaves + concat with audio. Drop one label and you'll see Output pad "out1" ... not connected.
• amovie / movie are lavfi source filters, not input flags. Use them INSIDE the -f lavfi graph string, not as -i.
• -ss is a start offset, not an output-side seek. You cannot put -ss after an input or combine it with -to; use -t for duration.
• Exit status is not useful for automation. ffplay is interactive. Use -autoexit to quit at EOF; use -nodisp to avoid needing a display. For CI/QA scripts, prefer ffmpeg with -f null - for filter validation.
• -stats is on by default in newer builds — disable with -nostats if it clutters your log.
• High-DPI displays: -x / -y are logical pixels on macOS/Wayland — the actual backing store is 2× on Retina.
• Keyboard focus is per-window. Tmux / screen multiplexers don't forward keys to ffplay; you must focus the SDL window.
• -loop 0 means loop forever; -loop 1 plays once (default); -loop N plays N times. Mirrors ffmpeg's output-side -loop semantics but confusingly named.

Examples

Example 1 — Iterate on a color filter before a final encode

# Live preview while tuning
ffplay -vf "eq=contrast=1.1:brightness=0.05:saturation=1.1,unsharp=5:5:0.8" in.mp4
# Press w mid-playback to A/B toggle. When happy, commit with ffmpeg:
ffmpeg -i in.mp4 -vf "eq=contrast=1.1:brightness=0.05:saturation=1.1,unsharp=5:5:0.8" -c:a copy out.mp4

Example 2 — Is the audio too loud?

ffplay -f lavfi "amovie=mix.wav,ebur128=video=1:meter=18[out0][out1]"
# Read integrated LUFS bottom-left, short-term/momentary bars right side.
# If I > -14 LUFS, normalize with: ffmpeg -af loudnorm=I=-16:LRA=11:TP=-1.5 ...

Example 3 — AV is drifting after a concat

ffplay -sync ext concat_out.mp4
# If drift accumulates linearly, the concat inputs had different timebases.
# Re-do the concat with: -vf setpts=PTS-STARTPTS -af asetpts=PTS-STARTPTS,aresample=async=1

Example 4 — Preview an ffmpeg pipe without writing a file

ffmpeg -i in.mov -vf scale=640:-2 -c:v libx264 -preset ultrafast -f matroska - | ffplay -i -

Keyboard shortcuts (full table in references/commands.md)

• Space / p — pause/play
• s — step one frame forward
• Left / Right — seek ±10s
• Down / Up — seek ±1min
• PgDown / PgUp — seek to previous/next chapter (or ±10min)
• f — toggle fullscreen
• w — cycle video filters (ffplay-only, for A/B)
• a / v / t / c — cycle audio / video / subtitle / program stream
• m — mute
• 9 / 0 — volume down / up
• q / Esc — quit
• Left-click on video — seek to that horizontal position (% of duration)
• Right-click / drag — seek by percent

Available scripts

• scripts/play.py — stdlib-only argparse wrapper around ffplay with subcommands: preview, filter-test, waveform, spectrum, vectorscope, loudness-meter, sync. Flags: --dry-run, --verbose. Prints the command before running, and downgrades to -nodisp when no DISPLAY is detected.

Workflow

python3 ${CLAUDE_SKILL_DIR}/scripts/play.py preview --input in.mp4 --start 60 --duration 10
python3 ${CLAUDE_SKILL_DIR}/scripts/play.py filter-test --input in.mp4 --vf "scale=1280:-2,eq=brightness=0.1"
python3 ${CLAUDE_SKILL_DIR}/scripts/play.py loudness-meter --input in.mp3
python3 ${CLAUDE_SKILL_DIR}/scripts/play.py sync --input in.mp4 --mode ext

Reference docs

• Read references/commands.md for the full keyboard shortcut table, every ffplay flag, the lavfi visualization catalog, SDL audio env vars, pipe recipes, and headless troubleshooting.

Troubleshooting

Error: Could not initialize SDL - No available video device

Cause: no DISPLAY / Wayland / Quartz session (headless SSH, container, CI). Solution: add -nodisp for audio-only; or X-forward with ssh -Y; or run under VNC/xvfb. SDL_VIDEODRIVER=dummy starts SDL but shows nothing — equivalent to -nodisp with extra steps.

Error: Output pad "out1" with type audio of the filtergraph is not connected to any destination

Cause: -f lavfi graph has only a video sink but the source (e.g. amovie) also produces audio, or you used ebur128=video=1 which emits both pads. Solution: terminate with [out0][out1] and keep both audio + video, e.g. ...ebur128=video=1[out0][out1].

Error: Option 'ss' cannot be applied to output url

Cause: -ss placed after a -i or alongside -to. In ffplay, -ss is a global/input-side start offset only, given once. Solution: ffplay -ss 60 -t 10 in.mp4 — -ss first, -i is implicit.

Video plays but audio is silent

Causes (in order): SDL audio driver mismatch, default output device muted, decoder can't produce planar format SDL wants. Solution: set SDL_AUDIODRIVER=coreaudio (mac) / pulse / alsa; check system volume; re-run with -loglevel verbose and look for SDL_OpenAudioDevice errors.

AV out of sync on a file that plays fine in VLC

Cause: ffplay's default master clock is audio; if audio has gaps or VFR video has long frames, drift is visible. Solution: -sync ext to use wall clock; or preprocess with setpts=PTS-STARTPTS + aresample=async=1.

Keyboard shortcuts do nothing

Cause: SDL window doesn't have focus, or terminal is capturing keys. Solution: click the video window. On macOS, make sure a Terminal.app shortcut isn't swallowing the key.