#Containers

A container format packages video, audio, subtitles, and metadata into a single file. The container you choose determines which codecs you can use and how the file can be delivered to viewers.

Transcodely supports five container formats for file-based outputs, plus HLS and DASH for adaptive streaming (covered in Streaming).

#Container Overview

#Codec Compatibility

Video codecs by container:

Audio codecs by container:

The API validates codec-container combinations and returns a validation_error if you specify an unsupported pairing.

#MP4

The most widely supported container format. MP4 files play natively in every browser, operating system, and media player.

Features:

• Supports moov atom at the start (faststart) for progressive playback without downloading the full file
• Chapter markers, subtitle tracks, and metadata
• Broad tool and editor support

Best for: General delivery, social media uploads, progressive download, mobile playback

{
  "type": "mp4",
  "video": [
    {"codec": "h264", "resolution": "1080p", "quality": "standard"}
  ]
}

#WebM

Google’s open container format, designed for web delivery. WebM is the native container for VP9 and AV1 content on the web.

Features:

• Based on Matroska (MKV) container
• Royalty-free, no licensing costs
• Natively supported in Chrome, Firefox, and Edge
• Smaller overhead than MP4 for web delivery

Best for: Web-first delivery, open-source projects, VP9/AV1 content

{
  "type": "webm",
  "video": [
    {"codec": "vp9", "resolution": "1080p", "quality": "standard"}
  ]
}

#MKV

Matroska is the most flexible container format, supporting every codec Transcodely offers. It is the only container that accepts all four video codecs and all three audio codecs.

Features:

• Supports unlimited audio, video, and subtitle tracks
• Chapter markers and rich metadata
• No codec restrictions
• Not natively supported in most browsers (requires a player like VLC)

Best for: Archival, internal processing, maximum flexibility, multi-track content

{
  "type": "mkv",
  "video": [
    {"codec": "av1", "resolution": "2160p", "quality": "premium"}
  ]
}

#MOV

Apple’s QuickTime container format. MOV is commonly used in professional video production workflows and is natively supported on macOS and iOS.

Features:

• Native support in Final Cut Pro, Motion, and other Apple tools
• ProRes support (source format, not transcoding target)
• Timecode tracks for professional editing
• Limited to H.264 and H.265 video codecs

Best for: Apple ecosystem, professional editing, Final Cut Pro workflows

{
  "type": "mov",
  "video": [
    {"codec": "h265", "resolution": "2160p", "quality": "premium"}
  ]
}

#TS (MPEG Transport Stream)

The broadcast industry standard for reliable video transport. TS is designed for environments where data loss is expected (satellite, cable TV).

Features:

• Error resilience — playback can recover from data corruption
• Fixed-size packets (188 bytes) for broadcast compatibility
• Limited to H.264/H.265 video and AAC/MP3 audio
• Commonly used as HLS segment format (legacy)

Best for: Broadcast workflows, legacy HLS infrastructure, satellite distribution

{
  "type": "ts",
  "video": [
    {"codec": "h264", "resolution": "1080p", "quality": "standard"}
  ]
}

#Choosing a Container

For most web applications, MP4 with H.264 is the safest choice. If you need better compression for modern browsers, use WebM with VP9 or MP4 with AV1 as a secondary format.