Enable adjustable codec multithreading (#332)

* enable adjustable multithreaded decoding

* enable 2 threads during CI

* also enable multithreaded encoding

* default threading for encode, Sys.CPU_THREADS for decode

* Revert "enable 2 threads during CI"

This reverts commit ffd91cc.

src/avio.jl

@@ -248,7 +248,8 @@ function VideoReader(avin::AVInput{I}, video_stream = 1;
  target_colorspace_details = nothing,
  allow_vio_gray_transform = true,
  swscale_options::OptionsT = (;),
- sws_color_options::OptionsT = (;)) where I
+ sws_color_options::OptionsT = (;),
+ thread_count::Union{Nothing, Int} = Sys.CPU_THREADS) where I
  bad_px_type = transcode && target_format !== nothing &&
  !is_pixel_type_supported(target_format)
  bad_px_type && error("Unsupported pixel format $target_format")
@@ -268,6 +269,7 @@ function VideoReader(avin::AVInput{I}, video_stream = 1;
 
  # Create decoder context
  codec_context = AVCodecContextPtr(codec) # Allocates
+ codec_context.thread_count = thread_count === nothing ? codec_context.thread_count : thread_count
  # Transfer parameters to decoder context
  ret = avcodec_parameters_to_context(codec_context, stream.codecpar)
  ret < 0 && error("Could not copy the codec parameters to the decoder")
@@ -584,6 +586,8 @@ arguments listed below.
 - `sws_color_options::OptionsT = (;)`: Additional keyword arguments passed to
  [sws_setColorspaceDetails]
  (http://ffmpeg.org/doxygen/2.5/group__libsws.html#ga541bdffa8149f5f9203664f955faa040).
+- `thread_count::Union{Nothing, Int} = Sys.CPU_THREADS`: The number of threads the codec is
+ allowed to use or `nothing` for default codec behavior. Defaults to `Sys.CPU_THREADS`.
 """
 openvideo(s::Union{IO, AbstractString, AVInput}, args...; kwargs...) =
  VideoReader(s, args...; kwargs...)

src/encoding.jl

@@ -240,7 +240,8 @@ function VideoWriter(filename::AbstractString, ::Type{T},
  pix_fmt_loss_flags = 0,
  input_colorspace_details = nothing,
  allow_vio_gray_transform = true,
- sws_color_options::OptionsT = (;)) where T
+ sws_color_options::OptionsT = (;),
+ thread_count::Union{Nothing, Int} = nothing) where T
  framerate > 0 || error("Framerate must be strictly positive")
 
  if haskey(encoder_options, :priv_data)
@@ -300,6 +301,7 @@ function VideoWriter(filename::AbstractString, ::Type{T},
  codec_context.time_base = target_timebase
  codec_context.framerate = framerate_rat
  codec_context.pix_fmt = encoding_pix_fmt
+ codec_context.thread_count = thread_count === nothing ? codec_context.thread_count : thread_count
 
  if format_context.oformat.flags & AVFMT_GLOBALHEADER != 0
  codec_context.flags |= AV_CODEC_FLAG_GLOBAL_HEADER
@@ -453,6 +455,8 @@ occurred.
 - `sws_color_options::OptionsT = (;)`: Additional keyword arguments passed to
  [sws_setColorspaceDetails]
  (http://ffmpeg.org/doxygen/2.5/group__libsws.html#ga541bdffa8149f5f9203664f955faa040).
+- `thread_count::Union{Nothing, Int} = nothing`: The number of threads the codec is
+ allowed to use, or `nothing` for default codec behavior. Defaults to `nothing`.
 
 See also: [`write`](@ref), [`close_video_out!`](@ref)
 """