diff --git a/docs/src/devnotes.md b/docs/src/devnotes.md
index 5fd968c8..ccae4124 100644
--- a/docs/src/devnotes.md
+++ b/docs/src/devnotes.md
@@ -41,6 +41,7 @@ default buffer size is 16KiB for each.
 - `error`: exception returned by the codec (`<:Error`)
 - `buffer1`: data buffer that is closer to the user (`<:Buffer`)
 - `buffer2`: data buffer that is farther to the user (`<:Buffer`)
+- `bytes_written_out`: number of bytes written to the underlying stream (`<:Int64`)
 
 The `mode` field may be one of the following value:
 - `:idle` : initial and intermediate mode, no buffered data
@@ -78,8 +79,10 @@ Shared buffers
 Adjacent transcoding streams may share their buffers. This will reduce memory
 allocation and eliminate data copy between buffers.
 
-`readdata!(input::IO, output::Buffer)` and `writedata!(output::IO,
-input::Buffer)` do the actual work of read/write data from/to the underlying
+If `buffer2` is shared it is considered to be owned by the underlying stream 
+by the `stats` and `position` functions.
+
+`readdata!(input::IO, output::Buffer)` and `flush_buffer2(stream::TranscodingStream)` do the actual work of read/write data from/to the underlying
 stream. These methods have a special pass for shared buffers.
 
 
diff --git a/fuzz/fuzz.jl b/fuzz/fuzz.jl
index ef36dcc5..8710e0ee 100644
--- a/fuzz/fuzz.jl
+++ b/fuzz/fuzz.jl
@@ -152,7 +152,25 @@ end
     )
     stream = wrap_stream(kws, IOBuffer())
     for i in 1:length(data)
+        position(stream) == i-1 || return false
+        if stream isa TranscodingStream
+            s = TranscodingStreams.stats(stream)
+            s.in == i-1 || return false
+            # TODO fix position(stream.stream)
+            # s.out == position(stream.stream) || return false
+            # s.transcoded_in == s.out || return false
+            # s.transcoded_out == s.out || return false
+        end
         write(stream, data[i]) == 1 || return false
     end
-    take_all(stream) == data
+    take_all(stream) == data || return false
+    if stream isa TranscodingStream
+        s = TranscodingStreams.stats(stream)
+        s.in == length(data) || return false
+        # TODO fix position(stream.stream)
+        # s.out == position(stream.stream) || return false
+        # s.transcoded_in == s.out || return false
+        # s.transcoded_out == s.out || return false
+    end
+    true
 end
\ No newline at end of file
diff --git a/src/noop.jl b/src/noop.jl
index 8b64d91b..cbdcf097 100644
--- a/src/noop.jl
+++ b/src/noop.jl
@@ -72,7 +72,7 @@ end
 function Base.seek(stream::NoopStream, pos::Integer)
     mode = stream.state.mode
     if mode === :write
-        flushbuffer(stream)
+        flush_buffer2(stream)
     end
     seek(stream.stream, pos)
     initbuffer!(stream.buffer1)
@@ -82,7 +82,7 @@ end
 function Base.seekstart(stream::NoopStream)
     mode = stream.state.mode
     if mode === :write
-        flushbuffer(stream)
+        flush_buffer2(stream)
     end
     seekstart(stream.stream)
     initbuffer!(stream.buffer1)
@@ -92,7 +92,7 @@ end
 function Base.seekend(stream::NoopStream)
     mode = stream.state.mode
     if mode === :write
-        flushbuffer(stream)
+        flush_buffer2(stream)
     end
     seekend(stream.stream)
     initbuffer!(stream.buffer1)
@@ -103,19 +103,23 @@ function Base.write(stream::NoopStream, b::UInt8)::Int
     changemode!(stream, :write)
     if has_sharedbuf(stream)
         # directly write data to the underlying stream
-        n = Int(write(stream.stream, b))
-        return n
+        write(stream.stream, b)
+        stream.state.bytes_written_out += 1
+    else
+        buffer1 = stream.buffer1
+        marginsize(buffer1) > 0 || flush_buffer2(stream)
+        writebyte!(buffer1, b)
     end
-    buffer1 = stream.buffer1
-    marginsize(buffer1) > 0 || flushbuffer(stream)
-    return writebyte!(buffer1, b)
+    return 1
 end
 
 function Base.unsafe_write(stream::NoopStream, input::Ptr{UInt8}, nbytes::UInt)::Int
     changemode!(stream, :write)
+    Int(nbytes) # Error if nbytes > typemax Int
     if has_sharedbuf(stream)
         # directly write data to the underlying stream
         n = Int(unsafe_write(stream.stream, input, nbytes))
+        stream.state.bytes_written_out += n
         return n
     end
     buffer = stream.buffer1
@@ -123,9 +127,10 @@ function Base.unsafe_write(stream::NoopStream, input::Ptr{UInt8}, nbytes::UInt):
         copydata!(buffer, input, Int(nbytes))
         return Int(nbytes)
     else
-        flushbuffer(stream)
+        flush_buffer2(stream)
         # directly write data to the underlying stream
         n = Int(unsafe_write(stream.stream, input, nbytes))
+        stream.state.bytes_written_out += n
         return n
     end
 end
@@ -148,17 +153,20 @@ function stats(stream::NoopStream)
     buffer = stream.buffer1
     @assert buffer === stream.buffer2
     if mode === :idle
-        consumed = supplied = 0
+        in = out = 0
     elseif mode === :read
-        supplied = buffer.transcoded
-        consumed = supplied - buffersize(buffer)
+        in = buffer.transcoded
+        out = in - buffersize(buffer)
     elseif mode === :write
-        supplied = buffer.transcoded + buffersize(buffer)
-        consumed = buffer.transcoded
+        out = stream.state.bytes_written_out
+        in = out
+        if !has_sharedbuf(stream)
+            in += buffersize(buffer)
+        end
     else
         throw_invalid_mode(mode)
     end
-    return Stats(consumed, supplied, supplied, supplied)
+    return Stats(in, out, out, out)
 end
 
 
@@ -190,24 +198,15 @@ function fillbuffer(stream::NoopStream; eager::Bool = false)::Int
     return nfilled
 end
 
-function flushbuffer(stream::NoopStream, all::Bool=false)
-    changemode!(stream, :write)
-    buffer = stream.buffer1
-    @assert buffer === stream.buffer2
-    nflushed::Int = 0
-    if all
-        while buffersize(buffer) > 0
-            nflushed += writedata!(stream.stream, buffer)
-        end
-    else
-        nflushed += writedata!(stream.stream, buffer)
-        makemargin!(buffer, 0)
-    end
-    buffer.transcoded += nflushed
-    return nflushed
+# Empty buffer1 by writing out data.
+# `stream` must be in :write mode.
+# Ensure there is margin available in buffer1 for at least one byte.
+function flush_buffer1(stream::NoopStream)::Nothing
+    flush_buffer2(stream)
 end
 
+# This is always called after `flush_buffer1(stream)`
 function flushuntilend(stream::NoopStream)
-    stream.buffer1.transcoded += writedata!(stream.stream, stream.buffer1)
+    @assert iszero(buffersize(stream.buffer1))
     return
 end
diff --git a/src/state.jl b/src/state.jl
index 0cb54b6c..134b9495 100644
--- a/src/state.jl
+++ b/src/state.jl
@@ -24,8 +24,11 @@ mutable struct State
     buffer1::Buffer
     buffer2::Buffer
 
+    # Number of bytes written to the underlying stream
+    bytes_written_out::Int64
+
     function State(buffer1::Buffer, buffer2::Buffer)
-        return new(:idle, :ok, false, Error(), buffer1, buffer2)
+        return new(:idle, :ok, false, Error(), buffer1, buffer2, Int64(0))
     end
 end
 
diff --git a/src/stream.jl b/src/stream.jl
index 22ef593f..ff7f0fda 100644
--- a/src/stream.jl
+++ b/src/stream.jl
@@ -494,21 +494,24 @@ function Base.write(stream::TranscodingStream)
     return 0
 end
 
-function Base.write(stream::TranscodingStream, b::UInt8)
+function Base.write(stream::TranscodingStream, b::UInt8)::Int
     changemode!(stream, :write)
-    if marginsize(stream.buffer1) == 0 && flushbuffer(stream) == 0
-        return 0
-    end
-    return writebyte!(stream.buffer1, b)
+    buffer1 = stream.buffer1
+    marginsize(buffer1) > 0 || flush_buffer1(stream)
+    writebyte!(buffer1, b)
+    return 1
 end
 
 function Base.unsafe_write(stream::TranscodingStream, input::Ptr{UInt8}, nbytes::UInt)
     changemode!(stream, :write)
-    state = stream.state
+    Int(nbytes) # Error if nbytes > typemax Int
     buffer1 = stream.buffer1
     p = input
     p_end = p + nbytes
-    while p < p_end && (marginsize(buffer1) > 0 || flushbuffer(stream) > 0)
+    while p < p_end
+        if marginsize(buffer1) ≤ 0
+            flush_buffer1(stream)
+        end
         m = min(marginsize(buffer1), p_end - p)
         copydata!(buffer1, p, m)
         p += m
@@ -535,7 +538,7 @@ const TOKEN_END = EndToken()
 
 function Base.write(stream::TranscodingStream, ::EndToken)
     changemode!(stream, :write)
-    flushbufferall(stream)
+    flush_buffer1(stream)
     flushuntilend(stream)
     return 0
 end
@@ -543,8 +546,8 @@ end
 function Base.flush(stream::TranscodingStream)
     checkmode(stream)
     if stream.state.mode == :write
-        flushbufferall(stream)
-        writedata!(stream.stream, stream.buffer2)
+        flush_buffer1(stream)
+        flush_buffer2(stream)
     end
     flush(stream.stream)
 end
@@ -600,9 +603,12 @@ function stats(stream::TranscodingStream)
         out = transcoded_out - buffersize(buffer1)
     elseif mode === :write
         transcoded_in = buffer1.transcoded
-        transcoded_out = buffer2.transcoded
+        out = state.bytes_written_out
+        transcoded_out = out
+        if !has_sharedbuf(stream)
+            transcoded_out += buffersize(buffer2)
+        end
         in = transcoded_in + buffersize(buffer1)
-        out = transcoded_out - buffersize(buffer2)
     else
         throw_invalid_mode(mode)
     end
@@ -633,38 +639,37 @@ function fillbuffer(stream::TranscodingStream; eager::Bool = false)
     return nfilled
 end
 
-function flushbuffer(stream::TranscodingStream, all::Bool=false)
-    changemode!(stream, :write)
+# Empty buffer1 by writing out data.
+# `stream` must be in :write mode.
+# Ensure there is margin available in buffer1 for at least one byte.
+function flush_buffer1(stream::TranscodingStream)::Nothing
     state = stream.state
     buffer1 = stream.buffer1
     buffer2 = stream.buffer2
-    nflushed::Int = 0
-    while (all ? buffersize(buffer1) != 0 : makemargin!(buffer1, 0) == 0)
+    while buffersize(buffer1) > 0
         if state.code == :end
             callstartproc(stream, :write)
         end
-        writedata!(stream.stream, buffer2)
-        Δin, _ = callprocess(stream, buffer1, buffer2)
-        nflushed += Δin
+        flush_buffer2(stream)
+        callprocess(stream, buffer1, buffer2)
     end
-    return nflushed
-end
-
-function flushbufferall(stream::TranscodingStream)
-    return flushbuffer(stream, true)
+    # move positions to the start of the buffer
+    @assert !iszero(makemargin!(buffer1, 0))
+    return
 end
 
+# This is always called after `flush_buffer1(stream)`
 function flushuntilend(stream::TranscodingStream)
-    changemode!(stream, :write)
     state = stream.state
     buffer1 = stream.buffer1
     buffer2 = stream.buffer2
+    @assert buffersize(buffer1) == 0
+    @assert stream.state.mode === :write
     while state.code != :end
-        writedata!(stream.stream, buffer2)
+        flush_buffer2(stream)
         callprocess(stream, buffer1, buffer2)
     end
-    writedata!(stream.stream, buffer2)
-    @assert buffersize(buffer1) == 0
+    flush_buffer2(stream)
     return
 end
 
@@ -687,7 +692,7 @@ function callprocess(stream::TranscodingStream, inbuf::Buffer, outbuf::Buffer)
     state = stream.state
     input = buffermem(inbuf)
     GC.@preserve inbuf makemargin!(outbuf, minoutsize(stream.codec, input))
-    Δin, Δout, state.code = GC.@preserve inbuf outbuf process(stream.codec, input, marginmem(outbuf), state.error)
+    Δin::Int, Δout::Int, state.code = GC.@preserve inbuf outbuf process(stream.codec, input, marginmem(outbuf), state.error)
     @debug(
         "called process()",
         code = state.code,
@@ -698,6 +703,12 @@ function callprocess(stream::TranscodingStream, inbuf::Buffer, outbuf::Buffer)
     )
     consumed!(inbuf, Δin, transcode = true)
     supplied!(outbuf, Δout, transcode = true)
+    if has_sharedbuf(stream)
+        if stream.state.mode === :write
+            # this must be updated before throwing any error if outbuf is shared.
+            stream.state.bytes_written_out += Δout
+        end
+    end
     if state.code == :error
         changemode!(stream, :panic)
     elseif state.code == :ok && Δin == Δout == 0
@@ -745,20 +756,28 @@ function readdata!(input::IO, output::Buffer)::Int
 end
 
 # Write all data to `output` from the buffer of `input`.
-function writedata!(output::IO, input::Buffer)
-    if output isa TranscodingStream && output.buffer1 === input
+function flush_buffer2(stream::TranscodingStream)::Nothing
+    output = stream.stream
+    buffer2 = stream.buffer2
+    state = stream.state
+    @assert state.mode === :write
+    if has_sharedbuf(stream)
         # Delegate the operation to the underlying stream for shared buffers.
-        return flushbufferall(output)
-    end
-    nwritten::Int = 0
-    while buffersize(input) > 0
-        n = GC.@preserve input Base.unsafe_write(output, bufferptr(input), buffersize(input))
-        consumed!(input, n)
-        nwritten += n
+        changemode!(output, :write)
+        flush_buffer1(output)
+    else
+        while buffersize(buffer2) > 0
+            n::Int = GC.@preserve buffer2 Base.unsafe_write(output, bufferptr(buffer2), buffersize(buffer2))
+            n ≤ 0 && error("short write")
+            consumed!(buffer2, n)
+            state.bytes_written_out += n
+            GC.safepoint()
+        end
+        # move positions to the start of the buffer
+        @assert !iszero(makemargin!(buffer2, 0))
         GC.safepoint()
     end
-    GC.safepoint()
-    return nwritten
+    nothing
 end
 
 
@@ -800,7 +819,7 @@ function changemode!(stream::TranscodingStream, newmode::Symbol)
         end
     elseif mode == :write
         if newmode == :close
-            flushbufferall(stream)
+            flush_buffer1(stream)
             flushuntilend(stream)
             state.mode = newmode
             finalize_codec(stream.codec, state.error)
diff --git a/test/codecdoubleframe.jl b/test/codecdoubleframe.jl
index 64b6d83a..ca0c8187 100644
--- a/test/codecdoubleframe.jl
+++ b/test/codecdoubleframe.jl
@@ -303,6 +303,89 @@ DoubleFrameDecoderStream(stream::IO; kwargs...) = TranscodingStream(DoubleFrameD
         end
     end
 
+    @testset "stats" begin
+        @testset "read" begin
+            stream = DoubleFrameEncoderStream(IOBuffer(b"foobar"))
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 0
+            @test stat.out == 0
+            read(stream)
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 6
+            @test stat.transcoded_in == 6
+            @test stat.transcoded_out == 16
+            @test stat.out == 16
+            close(stream)
+
+            #nested Streams
+            stream = DoubleFrameDecoderStream(DoubleFrameEncoderStream(IOBuffer(b"foobar")))
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 0
+            @test stat.out == 0
+            read(stream)
+            stat = TranscodingStreams.stats(stream)
+            @test_broken stat.in == 16
+            @test_broken stat.transcoded_in == 16
+            @test stat.transcoded_out == 6
+            @test stat.out == 6
+            close(stream)
+        end
+
+        @testset "write" begin
+            stream = DoubleFrameEncoderStream(IOBuffer())
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 0
+            @test stat.out == 0
+            write(stream, b"foobar")
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 6
+            @test stat.transcoded_in == 0
+            @test stat.transcoded_out == 0
+            @test stat.out == 0
+            flush(stream)
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 6
+            @test stat.transcoded_in == 6
+            @test stat.transcoded_out == 14
+            @test stat.out == 14
+            write(stream, TranscodingStreams.TOKEN_END)
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 6
+            @test stat.transcoded_in == 6
+            @test stat.transcoded_out == 16
+            @test stat.out == 16
+            close(stream)
+
+            #nested Streams
+            stream = DoubleFrameDecoderStream(DoubleFrameEncoderStream(IOBuffer()))
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 0
+            @test stat.out == 0
+            write(stream, b"[ ffoooobbaarr ]")
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 16
+            @test stat.transcoded_in == 0
+            @test stat.transcoded_out == 0
+            @test stat.out == 0
+            flush(stream)
+            stat = TranscodingStreams.stats(stream)
+            @test stat.in == 16
+            @test stat.transcoded_in == 16
+            @test stat.transcoded_out == 6
+            @test stat.out == 6
+            @test_broken position(stream.stream) == 6
+            close(stream)
+        end
+    end
+
+    @testset "underlying stream fails" begin
+        sink = IOBuffer(;maxsize=4)
+        stream = DoubleFrameEncoderStream(sink)
+        @test write(stream, "abcd") == 4
+        # make sure flush doesn't go into an infinite loop
+        @test_throws ErrorException("short write") flush(stream)
+    end
+
     test_roundtrip_read(DoubleFrameEncoderStream, DoubleFrameDecoderStream)
     test_roundtrip_write(DoubleFrameEncoderStream, DoubleFrameDecoderStream)
     test_roundtrip_lines(DoubleFrameEncoderStream, DoubleFrameDecoderStream)
diff --git a/test/codecnoop.jl b/test/codecnoop.jl
index 6203787b..abcd2751 100644
--- a/test/codecnoop.jl
+++ b/test/codecnoop.jl
@@ -171,22 +171,65 @@ using FillArrays: Zeros
     @test s1.buffer1 === s2.buffer1 === s3.buffer1 ===
           s1.buffer2 === s2.buffer2 === s3.buffer2
 
-    stream = TranscodingStream(Noop(), IOBuffer(b"foobar"))
-    @test TranscodingStreams.stats(stream).in === Int64(0)
-    @test TranscodingStreams.stats(stream).out === Int64(0)
-    read(stream)
-    @test TranscodingStreams.stats(stream).in === Int64(6)
-    @test TranscodingStreams.stats(stream).out === Int64(6)
-    close(stream)
+    @testset "stats" begin
+        stream = TranscodingStream(Noop(), IOBuffer(b"foobar"))
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(0)
+        @test stat.out === Int64(0)
+        eof(stream)
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(6)
+        @test stat.out === Int64(0)
+        read(stream)
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(6)
+        @test stat.out === Int64(6)
+        close(stream)
 
-    stream = TranscodingStream(Noop(), IOBuffer())
-    @test TranscodingStreams.stats(stream).in === Int64(0)
-    @test TranscodingStreams.stats(stream).out === Int64(0)
-    write(stream, b"foobar")
-    flush(stream)
-    @test TranscodingStreams.stats(stream).in === Int64(6)
-    @test TranscodingStreams.stats(stream).out === Int64(6)
-    close(stream)
+        #nested NoopStreams
+        stream = NoopStream(NoopStream(IOBuffer(b"foobar")))
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(0)
+        @test stat.out === Int64(0)
+        eof(stream)
+        stat = TranscodingStreams.stats(stream)
+        @test_broken stat.in === Int64(0)
+        @test stat.out === Int64(0)
+        read(stream)
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(6)
+        @test stat.out === Int64(6)
+        close(stream)
+
+        stream = TranscodingStream(Noop(), IOBuffer())
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(0)
+        @test stat.out === Int64(0)
+        write(stream, b"foobar")
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(6)
+        @test stat.out === Int64(0)
+        flush(stream)
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(6)
+        @test stat.out === Int64(6)
+        close(stream)
+
+        #nested NoopStreams
+        stream = NoopStream(NoopStream(IOBuffer()))
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(0)
+        @test stat.out === Int64(0)
+        write(stream, b"foobar")
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(6)
+        @test stat.out === Int64(6)
+        flush(stream)
+        stat = TranscodingStreams.stats(stream)
+        @test stat.in === Int64(6)
+        @test stat.out === Int64(6)
+        close(stream)
+    end
 
     stream = TranscodingStream(Noop(), IOBuffer())
     @test stream.state.mode == :idle