# Slow appendencode on Raspberry Pi

**URL:** <https://discourse.julialang.org/t/slow-appendencode-on-raspberry-pi/50504>\
**Category:** General Usage\
**Tags:** question\
**Created:** [November 20, 2020, 4:29pm UTC](https://discourse.julialang.org/t/slow-appendencode-on-raspberry-pi/50504 "2020-11-20T16:29:07Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![yakir12](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yakir12/32/297_2.png) [@yakir12](https://discourse.julialang.org/u/yakir12)\
**Post date:** [November 20, 2020, 4:29pm UTC](https://discourse.julialang.org/t/slow-appendencode-on-raspberry-pi/50504/1 "2020-11-20T16:29:08Z")

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On a Raspberry Pi in the following MWE:

```julia
using VideoIO, Dates, BenchmarkTools
cam = VideoIO.opencamera()
img = read(cam)
filename = "video.mp4"
framerate = 200
props = [:priv_data => ("crf"=>"0","preset"=>"ultrafast")]
encoder = prepareencoder(img, framerate=framerate, AVCodecContextProperties=props)
io = Base.open("temp.stream","w")
@btime appendencode!($encoder, $io, $img, 1)

```

it takes ~430 ms to encode a single frame to a video stream. On my PC it takes ~7 ms – 60 times faster video encoding.

This is a shame because it means we can’t use RPIs to capture, process, and encode live video in real time with a frame rate higher than ~2.

Maybe some of the RPI wizards can figure out what’s going on here?

Thanks in advance!

The RPI involved:

```julia
julia> versioninfo()
Julia Version 1.5.2
Commit 539f3ce* (2020-09-23 23:17 UTC)
Platform Info:
  OS: Linux (arm-linux-gnueabihf)
  CPU: ARMv7 Processor rev 3 (v7l)
  WORD_SIZE: 32
  LIBM: libopenlibm
  LLVM: libLLVM-9.0.1 (ORCJIT, cortex-a72)

```

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**Author:** ![dawbarton](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dawbarton/32/215461_2.png) [@dawbarton](https://discourse.julialang.org/u/dawbarton)\
**Post date:** [November 20, 2020, 5:10pm UTC](https://discourse.julialang.org/t/slow-appendencode-on-raspberry-pi/50504/2 "2020-11-20T17:10:04Z")

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Coincidentally, I was just trying something similar yesterday. I found that VideoIO by default transcodes into RGB (from the more usual YUV format that webcams produce) which slows down the data capture quite a bit. You could try disabling the transcoding (since it’s unnecessary if you are just piping out to a file) with the `transcode=false` in the `opencamera` call. However, that hits some only partially implemented code paths but I put a PR to VideoIO with some fixes in [https://github.com/JuliaIO/VideoIO.jl/pull/277](https://github.com/JuliaIO/VideoIO.jl/pull/277) but they could definitely use more testing.

That said, I’ve just noticed you aren’t actually timing the data acquisition…

On the encoding side, you could try to use the hardware accelerated encoder on the Pi - it’s the h264\_omx codec in FFMPEG (see, e.g., [https://askubuntu.com/questions/1224437/how-to-use-hardware-encoding-in-ffmpeg-h264-omx-on-raspberry-pi-4-running-ubun](https://askubuntu.com/questions/1224437/how-to-use-hardware-encoding-in-ffmpeg-h264-omx-on-raspberry-pi-4-running-ubun)). I don’t know if it’s compiled into the Julia binaries though. It might be possible to coerce VideoIO into using a different binary(?) that you’ve compiled yourself.

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<div class="post-metadata">

**Author:** ![yakir12](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yakir12/32/297_2.png) [@yakir12](https://discourse.julialang.org/u/yakir12)\
**Post date:** [November 20, 2020, 5:18pm UTC](https://discourse.julialang.org/t/slow-appendencode-on-raspberry-pi/50504/3 "2020-11-20T17:18:26Z")

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Wow, sounds promising! I think I can copypaste a build-script from `BinaryBuilder.jl` to build a version of `ffmpeg` that uses the `h264_omx` codec instead and then fork `VideoIO` and change its dependency to use _that_ `FFMPEG_jll` instead?

Ideally, installing `VideoIO` would involve checking which system it’s installed on and changing its dependency accordingly… But that sounds like science fiction.

I’ll give it a try. Currently it’s the only viable solution I have to move forward on this front.

Thank you so much!!!

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<div class="post-metadata">

**Author:** ![yakir12](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yakir12/32/297_2.png) [@yakir12](https://discourse.julialang.org/u/yakir12)\
**Post date:** [November 20, 2020, 5:56pm UTC](https://discourse.julialang.org/t/slow-appendencode-on-raspberry-pi/50504/4 "2020-11-20T17:56:57Z")

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> [@dawbarton](#):
>
> You could try disabling the transcoding (since it’s unnecessary if you are just piping out to a file) with the `transcode=false` in the `opencamera` call. However, that hits some only partially implemented code paths but I put a PR to VideoIO with some fixes in [Add code for non-transcoded video streams by dawbarton · Pull Request #277 · JuliaIO/VideoIO.jl · GitHub](https://github.com/JuliaIO/VideoIO.jl/pull/277) but they could definitely use more testing.

You mentioned you needed testing, on my RPI this:

```julia
using VideoIO, BenchmarkTools
cam = VideoIO.opencamera()
img = read(cam)
@btime read!($cam, $img)

```

results in 11.039 ms.  
Using your PR, and `transcode=false` results in 845.115 μs! A ~13 times speedup! So that PR sounds amazing 😀