Audio codecs

Common audio codecs next to the same H.264 or VP9 video, and files with no audio track at all, which some players treat as broken.

The files

18 files in snapshot 2026-11-02. Each one's full fact sheet and recipe: GET /v1/cases/{id}, no token needed.

• H.264 and AC-3 in Matroskaaudio-codec/h264-ac3.mkv Matroska1920x1080 H.264 at 30 fps, stereo AC-3 at 48 kHz, 6 s, 5.6 MB Facts
• H.264 and AC-3 in MP4audio-codec/h264-ac3.mp4 MP41920x1080 H.264 at 30 fps, stereo AC-3 at 48 kHz, 6 s, 5.6 MB Facts
• H.264 and ALAC in MOVaudio-codec/h264-alac.mov MOV1920x1080 H.264 at 30 fps, stereo ALAC at 48 kHz, 6 s, 5.6 MB Facts
• H.264 and E-AC-3 in MP4audio-codec/h264-eac3.mp4 MP41920x1080 H.264 at 30 fps, stereo E-AC-3 at 48 kHz, 6 s, 5.5 MB Facts
• H.264 and FLAC in Matroskaaudio-codec/h264-flac.mkv Matroska1920x1080 H.264 at 30 fps, stereo FLAC at 48 kHz, 6 s, 5.5 MB Facts
• H.264 and FLAC in MP4audio-codec/h264-flac.mp4 MP41920x1080 H.264 at 30 fps, stereo FLAC at 48 kHz, 6 s, 5.5 MB Facts
• H.264 and MP3 in Matroskaaudio-codec/h264-mp3.mkv Matroska1920x1080 H.264 at 30 fps, stereo MP3 at 48 kHz, 6 s, 5.5 MB Facts
• H.264 and MP3 in MP4audio-codec/h264-mp3.mp4 MP41920x1080 H.264 at 30 fps, stereo MP3 at 48 kHz, 6 s, 5.5 MB Facts
• H.264 in Matroska, no audioaudio-codec/h264-none.mkv Matroska1920x1080 H.264 at 30 fps, 6 s, 5.4 MB Facts
• H.264 in MOV, no audioaudio-codec/h264-none.mov MOV1920x1080 H.264 at 30 fps, 6 s, 5.4 MB Facts
• H.264 in MP4, no audioaudio-codec/h264-none.mp4 MP41920x1080 H.264 at 30 fps, 6 s, 5.4 MB Facts
• H.264 and Opus in Matroskaaudio-codec/h264-opus.mkv Matroska1920x1080 H.264 at 30 fps, stereo Opus at 48 kHz, 6 s, 5.5 MB Facts
• H.264 and Opus in MP4audio-codec/h264-opus.mp4 MP41920x1080 H.264 at 30 fps, stereo Opus at 48 kHz, 6 s, 5.5 MB Facts
• H.264 and 16-bit PCM in MOVaudio-codec/h264-pcm.mov MOV1920x1080 H.264 at 30 fps, stereo 16-bit PCM at 48 kHz, 6 s, 6.6 MB Facts
• H.264 and 16-bit PCM in MP4audio-codec/h264-pcm.mp4 MP41920x1080 H.264 at 30 fps, stereo 16-bit PCM at 48 kHz, 6 s, 6.6 MB Facts
• H.264 and Vorbis in Matroskaaudio-codec/h264-vorbis.mkv Matroska1920x1080 H.264 at 30 fps, stereo Vorbis at 48 kHz, 6 s, 5.4 MB Facts
• VP9 in WebM, no audioaudio-codec/vp9-none.webm WebM1920x1080 VP9 at 30 fps, 6 s, 5.2 MB Facts
• VP9 and Vorbis in WebMaudio-codec/vp9-vorbis.webm WebM1920x1080 VP9 at 30 fps, stereo Vorbis at 48 kHz, 6 s, 5.2 MB Facts

What's in every file

Every video carries its frame number and timecode, burned in at the top left, a frame code along the bottom that the checker reads, and a white flash in the first three frames of every second. The audio carries a tone with a 40 ms beep at the start of every second. So a test can tell which frame is on screen, whether any were dropped, and whether sound and picture line up.

How they were verified

Before publishing, every file was probed and decoded by FFmpeg 7.1.5-0+deb13u1 and GStreamer 1.26.2 (sidecar subtitle files are probed only), and every file with video was played through the testsrc checker, which reads the frame code to confirm frames, timing, orientation, aspect and colour.

Use them

# one file's facts
curl https://testsrc.com/v1/cases/audio-codec/h264-ac3.mkv

# play every file in this category through your player and check what it showed
testsrc run --player libvlc audio-codec/

See the API reference for tokens, quotas and snapshots.

Other baseline categories