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mpeg-audio-frame-parser
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Bug fix: Complete frames as soon as it is possible 

It should not be necessary to wait for the subsequent sync word to
determine that the current frame is complete - this can be assured
simply back checking the expected frame size against the actual bytes.

This ensures that completed frames are made available immediately, and
avoids dropping a single frame from every binary stream that is
processed.
This commit is contained in:
Rob Watson 2018-04-18 12:42:54 +02:00
parent 82f661cc25
commit f9d6c66f7e
4 changed files with 24 additions and 46 deletions
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8
lib/mpeg_audio_frame_parser.ex
View File

@ -36,9 +36,7 @@ defmodule MPEGAudioFrameParser do
## Example
Using a faked 128kbps 44.1k stereo MP3 frame. Note at least two headers must
be processed to return a single MP3 frame - otherwise frame completeness
couldn't be assured:
Using a faked 128kbps 44.1k stereo MP3 frame:
iex> packet = <<0b11111111111_11_01_0_1001_00_0_0_00_00_0_0_00::size(32), 1::size(3304)>>
...> {:ok, _pid} = MPEGAudioFrameParser.start_link()
@ -74,9 +72,7 @@ defmodule MPEGAudioFrameParser do
## Example
Using a faked 128kbps 44.1k stereo MP3 frame. Note at least two headers must
be processed to return a single MP3 frame - otherwise frame completeness
couldn't be assured:
Using a faked 128kbps 44.1k stereo MP3 frame:
iex> packet = <<0b11111111111_11_01_0_1001_00_0_0_00_00_0_0_00::size(32), 1::size(3304)>>
...> {:ok, _pid} = MPEGAudioFrameParser.start_link()

13
lib/mpeg_audio_frame_parser/impl.ex
View File

@ -28,6 +28,12 @@ defmodule MPEGAudioFrameParser.Impl do
# Private Functions
# Synced, and the current frame is complete:
defp process_bytes(%{current_frame: %Frame{complete: true}} = state, packet) do
frames = [state.current_frame | state.frames]
process_bytes(%{state | current_frame: nil, frames: frames}, packet)
end
# No data left, or not enough to be able to validate next frame. Return:
defp process_bytes(state, packet)
when bit_size(packet) < 32
@ -62,13 +68,6 @@ defmodule MPEGAudioFrameParser.Impl do
process_bytes(%{state | current_frame: nil}, rest)
end
# Synced, and the current frame is complete:
defp process_bytes(%{current_frame: %Frame{complete: true}} = state, packet) do
frames = [state.current_frame | state.frames]
new_state = %{state | current_frame: nil, frames: frames}
process_bytes(new_state, packet)
end
# Synced, current frame not complete and we have bytes available. Add bytes to frame:
defp process_bytes(%{current_frame: %Frame{complete: false}} = state, packet) do
{:ok, frame, rest} = Frame.add_bytes(state.current_frame, packet)

10
test/integration_test.exs
View File

@ -3,27 +3,27 @@ defmodule MPEGAudioFrameParserIntegrationTest do
test "128kbps 44100hz MP3" do
MPEGAudioFrameParser.start_link()
assert count_frames("test/fixtures/test_128_44100.mp3") == 253
assert count_frames("test/fixtures/test_128_44100.mp3") == 254
end
test "64kbps 12000hz MP3" do
MPEGAudioFrameParser.start_link()
assert count_frames("test/fixtures/test_64_12000.mp3") == 139
assert count_frames("test/fixtures/test_64_12000.mp3") == 140
end
test "160kbps 24000hz MP3" do
MPEGAudioFrameParser.start_link()
assert count_frames("test/fixtures/test_160_24000.mp3") == 276
assert count_frames("test/fixtures/test_160_24000.mp3") == 277
end
test "128kbps 44100hz MP3 with CRC protection" do
MPEGAudioFrameParser.start_link()
assert count_frames("test/fixtures/test_128_44100_crc_protection.mp3") == 253
assert count_frames("test/fixtures/test_128_44100_crc_protection.mp3") == 254
end
test "64kbps 22050hz MP2" do
MPEGAudioFrameParser.start_link()
assert count_frames("test/fixtures/test_64_22050.mp2") == 125
assert count_frames("test/fixtures/test_64_22050.mp2") == 126
end
defp count_frames(path) do

39
test/mpeg_audio_frame_parser/impl_test.exs
View File

@ -13,12 +13,9 @@ defmodule MPEGAudioFrameParser.ImplTest do
test "handles a single frame at the start of a packet" do
{:ok, state} = init()
{:ok, state} = add_packet(state, @frame1)
assert state.current_frame.data == @frame1
assert state.current_frame.complete
assert state.frames == []
assert %{current_frame: nil, frames: [%{data: @frame1}]} = state
end
test "handles a single frame in the middle of a packet" do
@ -27,9 +24,7 @@ defmodule MPEGAudioFrameParser.ImplTest do
packet = <<0, 1, 2, 3, @frame1::binary>>
{:ok, state} = add_packet(state, packet)
assert state.current_frame.data == @frame1
assert state.current_frame.complete
assert state.frames == []
assert %{current_frame: nil, frames: [%{data: @frame1}]} = state
end
test "ignores a packet that includes no valid frames at all" do
@ -37,8 +32,7 @@ defmodule MPEGAudioFrameParser.ImplTest do
{:ok, state} = add_packet(state, <<1::size(10240)>>)
assert state.frames == []
assert state.current_frame == nil
assert %{current_frame: nil, frames: []} = state
end
test "handles two frames in consecutive packets" do
@ -47,9 +41,7 @@ defmodule MPEGAudioFrameParser.ImplTest do
{:ok, state} = add_packet(state, @frame1)
{:ok, state} = add_packet(state, @frame3)
assert length(state.frames) == 1
assert List.first(state.frames).data == @frame1
assert state.current_frame.data == @frame3
assert %{current_frame: nil, frames: [%{data: @frame3}, %{data: @frame1}]} = state
end
test "handles a frame split unevenly across consecutive packets" do
@ -57,13 +49,9 @@ defmodule MPEGAudioFrameParser.ImplTest do
part1 = :binary.part(@frame1, {0, 256})
part2 = :binary.part(@frame1, {byte_size(@frame1), -(byte_size(@frame1) - 256)})
part3 = :binary.part(@frame3, {0, 256})
packet = <<8, 0, 1, 0, 0, 0, 7, 90, 93, part1::binary>>
{:ok, state} = add_packet(state, packet)
packet = <<part2::binary, part3::binary>>
{:ok, state} = add_packet(state, packet)
{:ok, state} = add_packet(state, <<0, 1, 2, 3, part1::binary>>)
{:ok, state} = add_packet(state, part2)
assert length(state.frames) == 1
assert List.first(state.frames).data == @frame1
@ -71,23 +59,21 @@ defmodule MPEGAudioFrameParser.ImplTest do
test "handles three frames in a single packet" do
{:ok, state} = init()
{:ok, state} = add_packet(state, <<@frame1::binary, @frame1::binary, @frame1::binary>>)
assert length(state.frames) == 2
assert Enum.map(state.frames, & &1.data) == [@frame1, @frame1]
assert length(state.frames) == 3
assert Enum.map(state.frames, & &1.data) == [@frame1, @frame1, @frame1]
end
test "handles three frames in consecutive packets" do
{:ok, state} = init()
{:ok, state} = add_packet(state, @frame3)
{:ok, state} = add_packet(state, @frame3)
{:ok, state} = add_packet(state, @frame3)
assert length(state.frames) == 2
assert Enum.map(state.frames, & &1.data) == [@frame3, @frame3]
assert state.current_frame.data == @frame3
assert length(state.frames) == 3
assert Enum.map(state.frames, & &1.data) == [@frame3, @frame3, @frame3]
assert is_nil(state.current_frame)
end
end
@ -104,8 +90,6 @@ defmodule MPEGAudioFrameParser.ImplTest do
{:ok, state} = init()
{:ok, state} = add_packet(state, @frame1)
{:ok, state} = add_packet(state, @frame1)
{:ok, frame, state} = pop_frame(state)
assert frame.data == @frame1
@ -117,7 +101,6 @@ defmodule MPEGAudioFrameParser.ImplTest do
{:ok, state} = add_packet(state, @frame1)
{:ok, state} = add_packet(state, @frame2)
{:ok, state} = add_packet(state, @frame1)
{:ok, frame, state} = pop_frame(state)
assert frame.data == @frame1