PLEASE do not confuse the i965 or iHD video driver with Subtitles. The two are NOT related.
i965 and iHD work in the hardware decode and encode layer. They have NO IMPACT on subtitles or Software encoding (ARM or non QSV-capable Xeon CPUs)
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i965 works best for H.264 and, on the N3xxx (H264), J33xx (H264), and J34xx (HEVC) CPUs, for less than 80 Mbps converted to less than 20 Mbps. This is why it’s very popular for those with anime or 720p output.
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iHD works best for anything above 50 Mbps source with output bitrate 20 Mbps or higher (“original quality H.264”). [ Personally, I use iHD (the default) in the entire house for everything because everything plays “Original Quality” ]
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The complaint that subtitle burning performance is unacceptable is without merit. Consider the following
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Whenever PMS must burn a subtitle on Synology – It is ALWAYS painful. This point has been acknowledged countless times. This is due to the extremely poor per-core speed of the CPUs used in Synology NAS products.
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The issue is rooted in the Passmark performance of the CPU.
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J3455 - 2254 total passmarks ( 563 / core )
PassMark - Intel Celeron J3455 @ 1.50GHz - Price performance comparison -
J4025 - 1633 total passmarks ( 408.25 / core-thread )
PassMark - Intel Celeron J4025 @ 2.00GHz - Price performance comparison -
I can grab all the results needed but the minimum for PMS to transcode in software (which is what subtitle burning is):
The actual process inside the transcoder
Source file
|
stream split
/ | \
Video / sub \ Audio
| | \
HW Decode | | audio transcoding (if needed on a CPU core)
| / |
| / |
Subtitle Burn (CPU) |
| |
HW Encode |
\ /
\ /
Multiplexer
|
|
V
H264, Subtitles burned into each image, with audio stream
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The Complaint is based on the poor single-thread performance of burning the subtitle stream into EACH frame of the video image before encoding. Intel did not write an API to do this in hardware even though the chip does appear to have an “image overlay” capability
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Playback stalls because , while the Video might be ready be decoded and the audio already transcoded, the subtitles have not been burned into the image.
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As each frame is finished, the hardware is capable of encoding to H.264 in microseconds.
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When all 3 streams are ready to be put back together into the composite stream for the player (time sync is required), the multiplexer creates the output H.264 stream and sends it to the player.
