Transcoding options #

This article lists the supported transcoding options in Nimbra Edge.

Limitations #

• Transcoding only supports transforming common video and audio streams. PIDs other than video and audio may be passed through but the behavior is undefined and may lead to unexpected results such as crashes and corrupted output data.

• Transcoding MPTS streams is not supported.

• MPEG-TS PIDs will be reassigned during transcoding.

Video Transcoding #

Video Transcoding is ideally performed on an appliance with an attached accelerator. If no accelerator is available, or if the desired settings are incompatible with the available accelerator, transcoding will run on the CPU. Details on supported accelerators can be found on the Transcoding accelerators page.

Video transcoding is a resource intensive task and may affect the performance of other services running on the same node. Ensure adequate testing is performed on an isolated node before deploying to a production node.

Notes #

Bitrate control mode #

Defaults to VBR - Variable bitrate.

Total Bitrate #

Required when using CBR - Constant bitrate Bitrate control mode. In CBR mode the video encoder is held at the configured Video Bitrate (constant bitrate with HRD signalling for H.264) and null packets pad the transport stream to the mux rate, so the Total Bitrate must leave room for the video, the audio and about 5% transport stream overhead. A mux rate without that headroom overshoots and the output stops decoding.

Video Bitrate #

The bitrate value is a target for the encoder, meaning the actual bitrate may differ.

Framerate #

When converting framerate, extra frames will be dropped, or frames will be duplicated to match the target framerate. When not specified, the input framerate is retained.

Note: Framerate conversion is not motion compensated and may be perceived as choppy or unnatural. Not recommended unless halving or doubling framerate.

Scan #

Interlaced encoding (TFF and BFF) is not available when using H.265 codec.

H.262 #

H.262 encoding only supports 4:2:0 8-bit and 4:2:2 8-bit.

Force software decoding and processing #

Transcodes use hardware decoding and processing by default when supported by the selected accelerator. Enable this option when the hardware decoder does not support the input codec, profile, pixel format, bit depth, or resolution. Hardware encoding remains enabled unless Force software encoding is also enabled.

Existing NVIDIA transcodes created before this option was introduced retain their software-compatible processing path until the option is changed.

Force software encoding #

When enabled, transcoding runs on the CPU even if a compatible hardware accelerator is available. Software encoding is slower but may produce higher quality output at the cost of increased CPU usage. Incompatible with GPU selection.

Encoder selection #

Selects which Intel GPU to use for QuickSync hardware encoding on appliances with both integrated and discrete Intel GPUs. Values:

• Auto: use the discrete GPU if available, otherwise the integrated GPU.
• Integrated: use the integrated GPU (e.g. Intel UHD Graphics).
• Discrete: use the discrete GPU (e.g. Intel Arc).

If the selected GPU type is not present on the assigned appliance, the appliance will use whichever Intel GPU is available.

Audio Transcoding #

Audio Transcoding can be performed on any appliance, as it does not require an accelerator. Note that transcoding a large number of audio streams may impact the overall performance of the appliance.

Notes #

AAC Profile #

Use of the AAC profile parameters requires the AAC codec to be selected. AAC-LC is the default profile.

AAC Quality #

Use of the AAC quality parameters requires the AAC codec to be selected. Quality targets override the bitrate selection.

MP2 #

MP2 audio transcoding only supports the following bitrates, in kbps: 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384