Skip to content

fix: support signed composition offsets #141

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
varsill merged 3 commits into from
Sep 24, 2026
Merged

fix: support signed composition offsets #141

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
6916a58
fix: support signed composition offsets
maslowalex Sep 1, 2026
cf592d8
make test more explicit
maslowalex Sep 11, 2026
f03f856
Pin variables used in binary size() matches in tests
varsill Sep 24, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
5 changes: 4 additions & 1 deletion lib/membrane_mp4/container/schema_default.ex
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -282,7 +282,10 @@ defmodule Membrane.MP4.Container.Schema.Default do
{:list,
[
sample_count: :uint32,
sample_composition_offset: :uint32
sample_composition_offset:
{:uint32, when: {:version, value: 0}},
sample_composition_offset:
{:int32, when: {:version, value: 1}}
]}
]
],
Expand Down
32 changes: 17 additions & 15 deletions lib/membrane_mp4/movie_box/sample_table_box.ex
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -201,22 +201,24 @@ defmodule Membrane.MP4.MovieBox.SampleTableBox do
timescale: timescale,
composition_offsets: composition_offsets
}) do
composition_offsets
|> Enum.map(fn %{sample_count: count, sample_composition_offset: offset} ->
%{sample_count: count, sample_composition_offset: Helper.timescalify(offset, timescale)}
end)
|> then(
&[
ctts: %{
fields: %{
version: 0,
flags: 0,
entry_count: length(&1),
entry_list: &1
}
composition_offsets =
Enum.map(composition_offsets, fn %{sample_count: count, sample_composition_offset: offset} ->
%{sample_count: count, sample_composition_offset: Helper.timescalify(offset, timescale)}
end)

version =
if Enum.any?(composition_offsets, &(&1.sample_composition_offset < 0)), do: 1, else: 0

[
ctts: %{
fields: %{
version: version,
flags: 0,
entry_count: length(composition_offsets),
entry_list: composition_offsets
}
]
)
}
]
end

defp maybe_sample_sync(%{sync_samples: []}), do: []
Expand Down
22 changes: 16 additions & 6 deletions lib/membrane_mp4/movie_fragment_box.ex
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -34,11 +34,17 @@ defmodule Membrane.MP4.MovieFragmentBox do
@mdat_data_offset 8

@spec assemble(%{
sequence_number: integer,
elapsed_time: integer,
timescale: integer,
duration: integer,
samples_table: [%{sample_size: integer, sample_flags: integer}]
id: pos_integer,
sequence_number: non_neg_integer,
base_timestamp: non_neg_integer,
samples_table: [
%{
sample_size: non_neg_integer,
sample_flags: non_neg_integer,
sample_duration: non_neg_integer,
sample_composition_time_offset: integer
}
]
}) :: Container.t()
def assemble(config) do
config =
Expand Down Expand Up @@ -94,7 +100,7 @@ defmodule Membrane.MP4.MovieFragmentBox do
@trun_flags.sample_composition_time_offsets_present,
sample_count: config.sample_count,
samples: config.samples_table,
version: 0
version: trun_version(config.samples_table)
}
}
],
Expand All @@ -105,4 +111,8 @@ defmodule Membrane.MP4.MovieFragmentBox do
}
]
end

defp trun_version(samples) do
if Enum.any?(samples, &(&1.sample_composition_time_offset < 0)), do: 1, else: 0
end
end
Binary file added test/fixtures/isom/ref_video_hevc_bframes.mp4
View file
Open in desktop
Binary file not shown.
29 changes: 29 additions & 0 deletions test/membrane_mp4/demuxer/isom/transmuxing_test.exs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@ defmodule Membrane.MP4.Demuxer.ISOM.TransmuxingTest do
in_mp4[:moov].children[:trak].children[:thkd]

assert out_mp4[:mdat] == in_mp4[:mdat]

{in_mp4, out_mp4}
end

@tag :tmp_dir
Expand Down Expand Up @@ -56,6 +58,33 @@ defmodule Membrane.MP4.Demuxer.ISOM.TransmuxingTest do
perform_test(pipeline, in_path, out_path)
end

@tag :tmp_dir
test "single H265 track with B-frames", %{tmp_dir: dir} do
# Generated with:
# ffmpeg -f lavfi -i testsrc2=size=320x180:rate=30 -t 1 -an -c:v libx265
# -preset ultrafast -pix_fmt yuv420p
# -x265-params bframes=2:b-adapt=0:open-gop=0:keyint=30:min-keyint=30
# -movflags +negative_cts_offsets ref_video_hevc_bframes.mp4
in_path = "test/fixtures/isom/ref_video_hevc_bframes.mp4"
out_path = Path.join(dir, "out")

pipeline =
start_testing_pipeline!(
input_file: in_path,
output_file: out_path
)

{in_mp4, out_mp4} = perform_test(pipeline, in_path, out_path)

input_ctts = Container.get_box(in_mp4, [:moov, :trak, :mdia, :minf, :stbl, :ctts])
output_ctts = Container.get_box(out_mp4, [:moov, :trak, :mdia, :minf, :stbl, :ctts])

assert input_ctts.fields.version == 1
assert Enum.any?(input_ctts.fields.entry_list, &(&1.sample_composition_offset < 0))
assert output_ctts.fields.version == 1
assert Enum.any?(output_ctts.fields.entry_list, &(&1.sample_composition_offset < 0))
end

defp start_testing_pipeline!(opts) do
structure = [
child(:file, %Membrane.File.Source{location: opts[:input_file]})
Expand Down
41 changes: 40 additions & 1 deletion test/membrane_mp4/muxer/cmaf/integration_test.exs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,29 @@ defmodule Membrane.MP4.Muxer.CMAF.IntegrationTest do
:ok = Testing.Pipeline.terminate(pipeline)
end

test "video hevc with negative composition offsets" do
pipeline =
prepare_pipeline(:video_hevc,
add_dts_offset: false,
header_file: "ref_video_hevc_header.mp4"
)

truns =
for _segment <- 1..2 do
assert_sink_buffer(pipeline, :sink, buffer)
assert_composition_offset_version(buffer.payload)

@varsill varsill Sep 10, 2026

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Hmm, do I get it right that we expect first segment to use version 1 box and the second segment to use version 0?
If so, I would prefer to explicitly assert on the desired box version that have assert_composition_offset_version determine the version itself, using the same logic that is used in the lib

end

assert Enum.any?(truns, fn trun ->
Enum.any?(trun.fields.samples, &(&1.sample_composition_time_offset < 0))
end)

assert_end_of_stream(pipeline, :sink)
refute_sink_buffer(pipeline, :sink, _buffer, 0)

:ok = Testing.Pipeline.terminate(pipeline)
end

test "audio" do
pipeline = prepare_pipeline(:audio)

Expand Down Expand Up @@ -437,7 +460,10 @@ defmodule Membrane.MP4.Muxer.CMAF.IntegrationTest do

:video_hevc ->
%Membrane.H265.Parser{
generate_best_effort_timestamps: %{framerate: {30, 1}},
generate_best_effort_timestamps: %{
framerate: {30, 1},
add_dts_offset: Keyword.get(opts, :add_dts_offset, true)
},
output_stream_structure: :hvc1
}
end
Expand Down Expand Up @@ -467,6 +493,19 @@ defmodule Membrane.MP4.Muxer.CMAF.IntegrationTest do
pipeline
end

defp assert_composition_offset_version(segment) do
assert {parsed_segment, <<>>} = Container.parse!(segment)
trun = Container.get_box(parsed_segment, [:moof, :traf, :trun])

expected_version =
if Enum.any?(trun.fields.samples, &(&1.sample_composition_time_offset < 0)),
do: 1,
else: 0

assert trun.fields.version == expected_version
trun
end

@fixtures_dir "test/fixtures/cmaf"
defp assert_mp4_equal(output, ref_file) do
{parsed_out, <<>>} = Container.parse!(output)
Expand Down
39 changes: 39 additions & 0 deletions test/membrane_mp4/muxer/isom/integration_test.exs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -254,5 +254,44 @@ defmodule Membrane.MP4.Muxer.ISOM.IntegrationTest do
assert Container.get_box(parsed_out, [:moov, :trak, :mdia, :minf, :stbl, :stts])
refute Container.get_box(parsed_out, [:moov, :trak, :mdia, :minf, :stbl, :ctts])
end

test "uses version 0 for non-negative composition offsets" do
ctts = mux_h265_and_get_ctts("video_hevc_ctts_v0", true)

assert ctts.fields.version == 0
assert Enum.all?(ctts.fields.entry_list, &(&1.sample_composition_offset >= 0))
end

test "uses version 1 for negative composition offsets" do
ctts = mux_h265_and_get_ctts("video_hevc_ctts_v1", false)

assert ctts.fields.version == 1
assert Enum.any?(ctts.fields.entry_list, &(&1.sample_composition_offset < 0))
end
end

defp mux_h265_and_get_ctts(filename, add_dts_offset) do
prepare_test(filename)

structure =
child(:file, %Membrane.File.Source{location: "test/fixtures/in_video_hevc.h265"})
|> child(:parser, %Membrane.H265.Parser{
generate_best_effort_timestamps: %{
framerate: {30, 1},
add_dts_offset: add_dts_offset
},
output_stream_structure: :hvc1
})
|> child(:muxer, %Membrane.MP4.Muxer.ISOM{chunk_duration: Time.seconds(1)})
|> child(:sink, %Membrane.File.Sink{location: out_path_for(filename)})

pid = Pipeline.start_link_supervised!(spec: structure)

assert_end_of_stream(pid, :sink, :input)
refute_sink_buffer(pid, :sink, _buffer, 0)
assert :ok == Pipeline.terminate(pid)

assert {parsed_out, <<>>} = out_path_for(filename) |> File.read!() |> Container.parse!()
Container.get_box(parsed_out, [:moov, :trak, :mdia, :minf, :stbl, :ctts])
end
end
Loading