H.264

H.264 (also known as AVC) is the most widely supported video codec. It plays on virtually every device, browser, and media player. Transcodely uses the libx264 encoder with sensible defaults that you can override per-output or per-variant.

Quick Start

The simplest H.264 output uses the defaults. Just specify the codec:

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

This produces a 1080p H.264 MP4 using the high profile, medium preset, and a CRF of 23 — suitable for most streaming applications.

H264Options Reference

Pass the h264 object on a video variant to override defaults:

{
  "codec": "h264",
  "resolution": "1080p",
  "quality": "standard",
  "h264": {
    "profile": "high",
    "preset": "slow",
    "crf": 20,
    "tune": "film"
  }
}

Presets

Presets control the encoding speed-to-compression tradeoff. Slower presets produce smaller files at the same quality.

Preset	Speed	Compression	Allowed
`ultrafast`	Fastest	Lowest	Yes
`superfast`	Very fast	Low	Yes
`veryfast`	Fast	Below average	Yes
`faster`	Above average	Average	Yes
`fast`	Average	Above average	Yes
`medium`	Below average	Good	Yes (default for standard tier)
`slow`	Slow	Very good	Yes (default for premium tier)
`slower`	Very slow	Excellent	Yes
`veryslow`	Extremely slow	Near-optimal	Not allowed
`placebo`	Impractical	Negligible gain	Not allowed

The veryslow and placebo presets are blocked because they provide minimal quality improvement at extreme encoding cost.

Default by quality tier:

Quality Tier	Default Preset	Default CRF
`economy`	`veryfast`	26
`standard`	`medium`	23
`premium`	`slow`	20

Profiles

Profiles define which H.264 features the encoder can use. Higher profiles enable better compression but require more capable decoders.

Profile	Features	Compatibility
`baseline`	No B-frames, no CABAC	Legacy devices, video conferencing
`main`	B-frames, CABAC	Mainstream devices
`high`	8x8 transforms, quantization scaling	Modern devices (default, recommended)

The high10, high422, and high444 profiles are not allowed due to limited playback support.

Levels

Levels cap the maximum bitrate, resolution, and frame rate. The encoder auto-selects the appropriate level by default. Override only if you need to target a specific device profile.

Level	Max Resolution	Max Framerate	Max Bitrate
`3.0`	720x576	25 fps	10 Mbps
`3.1`	1280x720	30 fps	14 Mbps
`4.0`	2048x1024	30 fps	20 Mbps
`4.1`	2048x1024	30 fps	50 Mbps
`4.2`	2048x1088	60 fps	50 Mbps
`5.0`	3672x1536	30 fps	135 Mbps
`5.1`	4096x2160	30 fps	240 Mbps
`5.2`	4096x2160	60 fps	240 Mbps

CRF (Constant Rate Factor)

CRF controls quality-based encoding. Lower values produce higher quality and larger files.

CRF Range	Quality	Use Case
15-18	Visually lossless	Archival, mastering
19-22	High quality	Premium streaming
23-25	Good quality	Standard streaming (default: 23)
26-30	Acceptable	Mobile, previews
31-35	Lower quality	Thumbnails, low-bandwidth

Allowed range: 15-35. Values below 15 produce near-lossless output (wasteful). Values above 35 produce poor quality.

CRF is mutually exclusive with bitrate. If you set both, the API returns a validation error.

Tune

Tune options optimize the encoder for specific content types:

Tune	Best For	Effect
`film`	Live-action film	Deblocking adjustments for natural content
`animation`	Cartoons, anime	Higher deblocking, more reference frames
`grain`	Film grain, vintage footage	Preserves grain texture
`stillimage`	Slideshows, screencasts	Optimized for static content
`fastdecode`	Low-power playback	Disables CABAC, fewer reference frames

The zerolatency tune is not allowed (reserved for live streaming, which Transcodely does not support).

Advanced Parameters

Parameter	Range	Default	Description
`bitrate`	100-240,000 kbps	None (CRF mode)	Target bitrate for size-based encoding
`maxrate`	100-240,000 kbps	None	Maximum bitrate for VBV buffering
`bufsize`	100-480,000 kbps	None	VBV buffer size
`keyint`	1-600 frames	250	Maximum keyframe interval (GOP size)
`min_keyint`	1-60 frames	25	Minimum keyframe interval
`bframes`	0-16	Per preset	Number of B-frames between I and P frames
`ref`	1-16	Per preset	Number of reference frames
`rc_lookahead`	0-250 frames	Per preset	Rate control lookahead distance
`aq_mode`	0-3	1	Adaptive quantization mode
`aq_strength`	0.0-3.0	1.0	Adaptive quantization strength
`psy_rd`	`"str:trellis"`	Per tune	Psychovisual rate-distortion optimization
`deblock`	`"alpha:beta"`	`"0:0"`	Deblocking filter strength (-6 to 6 each)

Example: High-Quality Film Encode

{
  "codec": "h264",
  "resolution": "1080p",
  "quality": "premium",
  "h264": {
    "profile": "high",
    "preset": "slow",
    "crf": 18,
    "tune": "film",
    "bframes": 8,
    "ref": 6,
    "aq_mode": 2,
    "aq_strength": 1.2
  }
}

Example: Fast Mobile-Friendly Encode

{
  "codec": "h264",
  "resolution": "720p",
  "quality": "economy",
  "h264": {
    "profile": "main",
    "preset": "veryfast",
    "crf": 28
  }
}

Container Compatibility

H.264 works with: MP4, MKV, MOV, TS, HLS, DASH

H.264 does not work with: WebM

#H.264

#Quick Start

#H264Options Reference

#Presets

#Profiles

#Levels

#CRF (Constant Rate Factor)

#Tune

#Advanced Parameters

#Example: High-Quality Film Encode

#Example: Fast Mobile-Friendly Encode

#Container Compatibility