Transmuxing vs. Transcoding: Essential techniques for optimizing video streaming

As global demand for high-quality, flexible video streaming continues to grow, expected to reach $606.77 billion by 2032, the need to understand and apply transmuxing and transcoding effectively is critical. These two processes may seem similar, but they have distinct roles within video streaming workflows. Transmuxing is focused on reformatting containers without changing underlying data, while transcoding re-encodes content to adjust bitrate, resolution, or codec, enabling more adaptable playback experiences.

In this blog, we’ll explore transmuxing and transcoding, highlighting specific use cases, relevant performance metrics, practical applications, and industry data to help guide your choices.

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Understanding transmuxing in video streaming

Transmuxing, or transformation of multiplexing, changes a video’s container format without modifying the underlying audio and video codecs. Containers, such as MP4, MKV, or HLS, act as wrappers around the media streams.
Transmuxing simply shifts content into a new container, making it a fast, low-resource solution when no quality loss or additional encoding is required. This approach is particularly useful for live streaming where low latency and real-time delivery are crucial.

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Real-world example: Low-latency live streaming

In live streaming, latency reduction directly impacts viewer retention. Studies show that viewers start to abandon a video if it takes more than 2 seconds to start up, with each incremental delay of 1 second resulting in a 5.8% increase in the abandonment rate. Transmuxing is perfect for live events as it repackages video without re-encoding, making the stream instantly adaptable to protocols like HLS or DASH. For instance, if your live feed is encoded in a compatible format, transmuxing allows it to be repackaged into an HLS stream for Apple TV devices within milliseconds.

Transmuxing metrics and performance indicators:

• Latency: Less than 500 milliseconds added, critical for real-time applications.
• Resource usage: Low CPU/GPU and memory requirements, typically reducing infrastructure costs by up to 50% compared to transcoding.
• Format compatibility: Enables playback on multiple devices without compromising the original content quality.

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Example: Transmuxing with FFmpeg

To repack an MP4 video into HLS format without changing codecs, use the following FFmpeg command:

ffmpeg -i input.mp4 -c copy -hls_time 6 -hls_list_size 0 -f hls output.m3u8

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Key parameters:

1. -c copy: Copies the video and audio codecs without re-encoding.
2. -hls_time 6: Breaks the video into 6-second segments for HLS.
3. -f hls: Specifies HLS output format for efficient adaptive streaming.

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Pros and cons of transmuxing

Pros

• Speed: Achieves near-instant format conversion, essential for live-streaming applications.
• Resource efficiency: Minimal CPU and memory requirements reduce operational costs.
• Quality assurance: Maintains original quality, suitable for content that’s pre-encoded in high-resolution formats.

Cons

Codec limitations: Since codecs are not altered, transmuxing doesn’t address compatibility issues for unsupported codecs on specific devices.
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Transcoding in video streaming

Transcoding, on the other hand, involves re-encoding video and audio data to a different codec, bitrate, or resolution. This process is vital for delivering content across a broad range of devices and adapting to diverse network conditions. Transcoding is essential for adaptive bitrate (ABR) streaming, which dynamically adjusts video quality based on network conditions to ensure seamless playback.

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Industry use case: Adaptive bitrate streaming (ABR)

ABR streaming has become an industry standard due to its impact on user experience 78% of viewers abandon videos that buffer frequently. In ABR, multiple versions of the same video are encoded at different bitrates and resolutions (e.g., 1080p, 720p, 480p). The player dynamically selects the optimal stream based on network and device conditions, helping reduce buffering and enhance viewer satisfaction. For example, Netflix encodes popular shows in five to eight different bitrates for ABR streaming, allowing users to switch seamlessly depending on their bandwidth.

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Transcoding metrics and key performance indicators

• Bitrate flexibility: Transcoded streams range from 144p to 4K to accommodate various network speeds and device capabilities.
• Latency impact: Re-encoding can add 2-5 seconds of delay, particularly for high-resolution outputs.
• Resource cost: Significantly higher CPU and GPU usage compared to transmuxing, requiring up to 10 times more processing power for HD and 4K streams.
• Quality trade-offs: Compression may impact quality, but settings like Constant rate factor (CRF) help balance quality with file size, particularly for ABR streaming.

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Example: Transcoding with FFmpeg

To convert a 4K HEVC video to Full HD H.264 for broad compatibility, you can use:

ffmpeg -i input_4k_hevc.mp4 -c:v libx264 -preset slow -crf 23 -c:a aac -b:a 128k -vf "scale=1920:1080" -b:v 5000k output_1080p_h264.mp4

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Parameters:

1. -c:v libx264: Sets the video codec to H.264, supported on most devices.
2. -crf 23: Controls quality, with **lower values producing higher quality**.
3. -vf "scale=1920:1080": Resizes video to Full HD, suitable for network-limited scenarios.
4. -b:v 5000k: Targets a bitrate suitable for Full HD, balancing quality with streaming efficiency.

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Pros and cons of transcoding

Pros

• Device compatibility: Increases the video’s accessibility across a wide array of devices and platforms.
• Quality customization: Allows you to tailor quality and resolution to suit storage or streaming requirements.
• Adaptive streaming: Supports ABR for smoother playback on fluctuating networks, reducing buffering.

Cons

• Higher costs: Transcoding demands high computational resources, increasing cloud or server expenses by up to 300% in some cases.
• Potential quality loss: Re-encoding inherently reduces quality unless managed with careful parameter tuning.

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Transmuxing vs. Transcoding: At-a-glance comparison

POST https://v1.fastpix.io/on-demand 
{
  "inputs": [
    {
      "type": "video",
      "url": "https://static.fastpix.io/sample.mp4"
    }
  ],
  "metadata": {
    "key1": "value1"
  },
  "accessPolicy": "public",
  "maxResolution": "1080p"
}

{
  "success": true,
  "data": {
    "id": "2104b7a9-549e-4c8e-a0db-efe48433db83",
    "trial": false,
    "status": "created",
    "createdAt": "2024-10-30T07:00:42.089421Z",
    "updatedAt": "2024-10-30T07:00:42.089425Z",
    "playbackIds": [
      {
        "id": "06345401-5654-4136-b3bf-a832cbae72cc",
        "accessPolicy": "public"
      }
    ],
    "metadata": {
      "key1": "value1"
    },
    "maxResolution": "1080p"
  }
}