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7 Commits
Author | SHA1 | Date |
---|---|---|
Rob Watson | 417f5d0545 | |
Rob Watson | d7d9b2e079 | |
Rob Watson | 395a6881ef | |
Rob Watson | 8c99f55145 | |
Rob Watson | 797a87ded8 | |
Rob Watson | 491b7462ca | |
Rob Watson | 510420d42d |
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@ -8,6 +8,13 @@ In theory supports all of MPEG layer 1, 2 and 3 and versions 1, 2 and 2.5, but i
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Currently WIP. See the [moduledoc](https://github.com/rfwatson/mpeg-audio-frame-parser/blob/master/lib/mpeg_audio_frame_parser.ex) for usage examples.
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## TODO
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* Validate CRC signature if present
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* Extract additional metadata (channel mode, copyright, etc)
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* Further tighten frame validation
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* Investigate improvements to public API/interface
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## Contributing
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Contributions welcome! Please ensure that appropriate automated tests are included with any pull requests.
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@ -7,8 +7,8 @@ defmodule MPEGAudioFrameParser.Frame do
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padding: 0,
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channel_mode: nil,
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data: <<>>,
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valid: false,
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complete: false
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length: 0,
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valid: false
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alias MPEGAudioFrameParser.Frame
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require Logger
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@ -20,48 +20,33 @@ defmodule MPEGAudioFrameParser.Frame do
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when is_binary(header)
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and bit_size(header) == @header_length
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do
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frame = %Frame{data: header}
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|> Map.put(:version_id, parse_version(header))
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|> Map.put(:layer, parse_layer(header))
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|> Map.put(:crc_protection, parse_crc_protection(header))
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|> Map.put(:bitrate, parse_bitrate(header))
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|> Map.put(:sample_rate, parse_sample_rate(header))
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|> Map.put(:padding, parse_padding(header))
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%{frame | valid: header_valid?(frame)}
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with version_id = parse_version(header),
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layer = parse_layer(header),
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crc_protection = parse_crc_protection(header),
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bitrate = parse_bitrate(header),
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sample_rate = parse_sample_rate(header),
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padding = parse_padding(header),
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valid = valid?(version_id, layer, bitrate, sample_rate),
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frame_length = frame_length(version_id, layer, bitrate, sample_rate, padding)
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do
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%Frame{
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data: header,
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version_id: version_id,
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layer: layer,
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crc_protection: crc_protection,
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bitrate: bitrate,
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sample_rate: sample_rate,
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padding: padding,
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valid: valid,
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length: frame_length,
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}
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end
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end
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def header_valid?(%Frame{version_id: version_id, layer: layer, bitrate: bitrate, sample_rate: sample_rate})
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when version_id != :reserved
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and layer != :reserved
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and bitrate != :bad
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and sample_rate != :bad
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do
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true
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end
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def header_valid?(%Frame{}), do: false
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def frame_length(%Frame{bitrate: bitrate, sample_rate: sample_rate} = frame)
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when is_integer(bitrate)
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and is_integer(sample_rate)
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do
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bits_per_frame = samples_per_frame(frame) / 8
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(bits_per_frame * (frame.bitrate * 1000) / frame.sample_rate + frame.padding)
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|> trunc
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end
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def frame_length(%Frame{}), do: 0
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def add_bytes(frame, packet) do
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limit = bytes_missing(frame)
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{:ok, bytes, rest, complete} = split_packet(packet, limit)
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{:ok, %{frame | data: frame.data <> bytes, complete: complete}, rest}
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end
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def bytes_missing(frame) do
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(frame_length(frame) - byte_size(frame.data))
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|> max(0)
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limit = frame.length - byte_size(frame.data) |> max(0)
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{:ok, bytes, rest} = split_packet(packet, limit)
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{:ok, %{frame | data: frame.data <> bytes}, rest}
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end
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# Private Functions
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@ -74,7 +59,7 @@ defmodule MPEGAudioFrameParser.Frame do
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part1 = :binary.part(packet, {0, bytes_to_take})
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part2 = :binary.part(packet, {bytes_available, -bytes_to_leave})
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{:ok, part1, part2, bytes_to_take == limit}
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{:ok, part1, part2}
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end
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defp parse_version(<<@sync_word::size(11), bits::size(2), _::bits>>), do: version_atom(bits)
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@ -184,26 +169,49 @@ defmodule MPEGAudioFrameParser.Frame do
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end
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defp parse_sample_rate(<<@sync_word::size(11), version_bits::size(2), _::size(7), sample_rate_bits::size(2), _::bits>>) do
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case {version_bits, sample_rate_bits} do
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{0b11, 0b00} -> 44100
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{0b11, 0b01} -> 48000
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{0b11, 0b10} -> 32000
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{0b10, 0b00} -> 22050
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{0b10, 0b01} -> 24000
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{0b10, 0b10} -> 16000
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{0b00, 0b00} -> 11025
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{0b00, 0b01} -> 12000
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{0b00, 0b10} -> 8000
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version_atom = version_atom(version_bits)
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case {version_atom, sample_rate_bits} do
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{:version1, 0b00} -> 44100
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{:version1, 0b01} -> 48000
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{:version1, 0b10} -> 32000
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{:version2, 0b00} -> 22050
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{:version2, 0b01} -> 24000
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{:version2, 0b10} -> 16000
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{:"version2.5", 0b00} -> 11025
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{:"version2.5", 0b01} -> 12000
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{:"version2.5", 0b10} -> 8000
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_ -> :bad
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end
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end
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defp parse_padding(<<@sync_word::size(11), _::size(11), 0b0::size(1), _::bits>>), do: 0
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defp parse_padding(<<@sync_word::size(11), _::size(11), 0b1::size(1), _::bits>>), do: 1
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defp parse_padding(<<@sync_word::size(11), _::size(11), padding_bit::size(1), _::bits>>), do: padding_bit
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defp samples_per_frame(%Frame{layer: :layer1}), do: 384
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defp samples_per_frame(%Frame{layer: :layer2}), do: 1152
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defp samples_per_frame(%Frame{layer: :layer3, version_id: :version1}), do: 1152
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defp samples_per_frame(%Frame{layer: :layer3, version_id: _}), do: 576
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defp samples_per_frame(%Frame{}), do: 0
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defp samples_per_frame(_, :layer1), do: 384
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defp samples_per_frame(_, :layer2), do: 1152
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defp samples_per_frame(:version1, :layer3), do: 1152
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defp samples_per_frame(_, :layer3), do: 576
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defp samples_per_frame(_, _), do: 0
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defp valid?(version_id, layer, bitrate, sample_rate)
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when version_id != :reserved
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and layer != :reserved
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and bitrate != :bad
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and sample_rate != :bad
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do
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true
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end
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defp valid?(_version_id, _layer, _bitrate, _sample_rate), do: false
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defp frame_length(version_id, layer, bitrate, sample_rate, padding)
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when is_integer(bitrate)
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and is_integer(sample_rate)
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do
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bits_per_frame = samples_per_frame(version_id, layer) / 8
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(bits_per_frame * (bitrate * 1000) / sample_rate + padding)
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|> trunc
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end
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defp frame_length(_version_id, _layer, _bitrate, _sample_rate, _padding), do: 0
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end
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@ -29,7 +29,9 @@ defmodule MPEGAudioFrameParser.Impl do
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# Private Functions
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# Synced, and the current frame is complete:
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defp process_bytes(%{current_frame: %Frame{complete: true}} = state, packet) do
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defp process_bytes(%{current_frame: %Frame{length: frame_length, data: data}} = state, packet)
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when frame_length == byte_size(data)
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do
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frames = [state.current_frame | state.frames]
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process_bytes(%{state | current_frame: nil, frames: frames}, packet)
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end
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@ -50,8 +52,7 @@ defmodule MPEGAudioFrameParser.Impl do
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# Not synced, found a sync word. Create a new frame struct:
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defp process_bytes(%{current_frame: nil} = state, <<@sync_word::size(11), header::size(21), rest::bits>>) do
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header = <<@sync_word::size(11), header::size(21)>>
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frame = Frame.from_header(header)
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frame = <<@sync_word::size(11), header::size(21)>> |> Frame.from_header
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process_bytes(%{state | current_frame: frame}, rest)
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end
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@ -63,13 +64,12 @@ defmodule MPEGAudioFrameParser.Impl do
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# Synced, but with an invalid header. Discard a byte:
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defp process_bytes(%{current_frame: %Frame{valid: false}} = state, packet) do
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data = <<state.current_frame.data, packet::bits>>
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<<_byte, rest::bits>> = data
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<<_byte, rest::bits>> = <<state.current_frame.data, packet::bits>>
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process_bytes(%{state | current_frame: nil}, rest)
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end
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# Synced, current frame not complete and we have bytes available. Add bytes to frame:
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defp process_bytes(%{current_frame: %Frame{complete: false}} = state, packet) do
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defp process_bytes(state, packet) do
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{:ok, frame, rest} = Frame.add_bytes(state.current_frame, packet)
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process_bytes(%{state | current_frame: frame}, rest)
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end
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@ -1,7 +1,7 @@
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defmodule MPEGAudioFrameParser.FrameTest do
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use ExUnit.Case
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alias MPEGAudioFrameParser.Frame
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import Frame, only: [from_header: 1, header_valid?: 1, frame_length: 1, bytes_missing: 1]
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import Frame, only: [from_header: 1]
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# MP3, 128kbps, no CRC protection, 44100hz, no padding, stereo
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@header1 <<0b11111111111_11_01_0_1001_00_0_0_00_00_0_0_00::size(32)>>
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@ -80,25 +80,21 @@ defmodule MPEGAudioFrameParser.FrameTest do
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end
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test "header validity" do
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assert from_header(@header1) |> header_valid?
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assert from_header(@header2) |> header_valid?
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assert from_header(@header3) |> header_valid?
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assert from_header(@header4) |> header_valid?
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assert from_header(@header5) |> header_valid?
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assert from_header(@header6) |> header_valid?
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refute from_header(@header7) |> header_valid?
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assert from_header(@header1).valid
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assert from_header(@header2).valid
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assert from_header(@header3).valid
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assert from_header(@header4).valid
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assert from_header(@header5).valid
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assert from_header(@header6).valid
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refute from_header(@header7).valid
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end
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test "frame_length" do
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assert from_header(@header1) |> frame_length == 417
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assert from_header(@header2) |> frame_length == 768
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assert from_header(@header3) |> frame_length == 105
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assert from_header(@header4) |> frame_length == 835
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assert from_header(@header5) |> frame_length == 208
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assert from_header(@header6) |> frame_length == 360
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end
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test "bytes missing" do
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assert from_header(@header1) |> bytes_missing == 413
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assert from_header(@header1).length == 417
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assert from_header(@header2).length == 768
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assert from_header(@header3).length == 105
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assert from_header(@header4).length == 835
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assert from_header(@header5).length == 208
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assert from_header(@header6).length == 360
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end
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end
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@ -0,0 +1,4 @@
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defmodule MPEGAudioFrameParserTest do
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use ExUnit.Case
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doctest MPEGAudioFrameParser
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end
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