Rework defining output stream formats by Noarkhh · Pull Request #25 · membraneframework/membrane_transcoder_plugin

Noarkhh · 2026-06-25T14:06:40Z

closes membraneframework/membrane_core#1152

Changes introduced by this PR:

Previously output format specification relied on stream formats, now OutputFormat provides module to be used when specifying the desired output format
Wrapped instantiation of VKVideo structs with Code.ensure_loaded?/1 calls
Previously, when input and output formats were structs of the same module, the transcoder just forwarded buffers and didn't create any elements. This approach ignored any differences between fields of these two stream formats. Now a parser is always inserted, making the stream conformant with output format

FelonEkonom · 2026-06-30T14:33:56Z

Please, fix CI

FelonEkonom

There one last thread unresolved

FelonEkonom

🚀 🚀 🚀

varsill · 2026-07-01T09:47:27Z

  defp deps do
    [
-      {:membrane_vk_video_plugin, "~> 0.2.0", optional: true},
+      # {:membrane_vk_video_plugin, "~> 0.2.0", optional: true},


don't you commit it ;)

varsill · 2026-07-01T09:48:13Z

  @test_cases @video_cases ++ @audio_cases

  Enum.map(@test_cases, fn test_case ->
+    @tag :base


Suggested change

@tag :base

FelonEkonom

Now I see that examples are not updated to the new API. Take a look at examples dir. It would be nice to have a test that runs examples and checks whenever they crash, to detect situations like this one.

FelonEkonom

What with running examples on CI? We could have a test, that runs both examples and checks if there is no error

FelonEkonom · 2026-07-02T09:16:39Z

 defmodule Example do
-  alias Membrane.{H264, H265, VP8, RCPipeline}
+  alias Membrane.{H264, RCPipeline}
+  alias Membrane.Transcoder.OutputFormat


I think that having alias for Membrane.Transcoder would be the prettiest in the example, right now we have Membrane.Transcoder in the child spec and OutputFormat.* in its opts, Trascoder and Transcoder.OutputFormat.* would be cleaner.

EDIT: it applies to the second example as well

Noarkhh · 2026-07-02T09:37:39Z

What with running examples on CI? We could have a test, that runs both examples and checks if there is no error

I think this something we should address in general, not just in this plugin. Maybe add a CI step that does that in test, it should be pretty straightforward

varsill

🥈 - just fix the CI ;)

FelonEkonom · 2026-07-08T13:04:41Z

I think this something we should address in general, not just in this plugin. Maybe add a CI step that does that in test, it should be pretty straightforward

What with examples that require some interaction, like opening a browser tab to inject a WebRTC stream?

Please, open an issue in membrane_core documenting this idea (or just implement it here 😉)

FelonEkonom

As far as I understood you correctly during todays meeting, this won't be ready to review until you implement these phillars, am I right?

varsill · 2026-07-27T13:21:55Z

      format when is_struct(format) ->
        format

      module when is_atom(module) ->
        struct(module)


Shouldn't we check agains a list of available OutputFormats here?
If somebody passes the old Membrane.H264, it will silently pass.

varsill · 2026-07-27T13:25:30Z

+        )
+
+      _other ->
+        builder


does it mean that e.g. for %Membrane.RemoteStream{content_format: Membrane.VP8} input and OutputFormat.V8 output configuration we will receive "unparsed" %Membrane.RemoteStream{content_format: Membrane.VP8} stream format from the output pad?

(I know that we don't have VP8 parser but I am just asking :D)

that's right, for now I thought that transcoding the stream just to parse it is ugly, but I'm not sure what would be the best

varsill · 2026-07-27T13:27:02Z

+        ) :: boolean()
+  defp should_be_transcoded(input_format, output_format, transcoding_policy, output_spec) do
+    transcoding_policy == :always or
+      output_spec.resolution != :keep or


And what if output resolution is explicitly provided, but equal to the input format resolution?

then it will be transcoded and rescaled nonetheless, I didn't add it for now

varsill · 2026-07-27T13:28:11Z

+
+  defmodule MPEGAudio do
+    @moduledoc """
+    Struct defining the desired output Membrane stream format.


Suggested change

Struct defining the desired output Membrane stream format.

Struct defining the desired output MPEGAudio stream format.

varsill · 2026-07-27T13:31:32Z

+        spec: bitrate_option() | :default,
+        default: :default,
        description: """
-        Per-output bitrate setting for video streams. Inherits from bin's `bitrate` option if nil.
+        Per-output bitrate setting for video streams.
+
+        Can be either:
+        * a `Membrane.Transcoder.Video.ConstantBitrate` struct for constant bitrate encoding
+        * a `Membrane.Transcoder.Video.VariableBitrate` struct for variable bitrate encoding
+        * `:default` - use encoder defaults


Perhaps we could raise if this option is set for audio pad? It might be misleading otherwise

varsill · 2026-07-27T13:45:34Z

+          | %Membrane.RemoteStream{content_format: Membrane.H264 | Membrane.H265}

-  An alternative to `t:#{inspect(__MODULE__)}.stream_format/0`.
+  @type audio_input_format ::


It's a duplicate of

membrane_transcoder_plugin/lib/transcoder/audio.ex

Line 27 in 2b791dd

@type audio_input_format ::

varsill · 2026-07-27T13:47:51Z

@@ -259,18 +300,40 @@ defmodule Membrane.Transcoder do

    spec = child(funnel_name, Funnel) |> bin_output(pad_ref)


[NIT] I know it's not a part of your change, but this Funnel could be Membrane.Connector

varsill · 2026-07-27T14:04:12Z

+
+      other_format ->
+        module_suffix = other_format.__struct__ |> Module.split() |> List.last()
+        struct!(Module.concat(OutputFormat, module_suffix))


Perhaps it would be good to have a whitelist of expected struct modules?

wrap VKVideo elements with ensure_loaded?

f391b08

Noarkhh self-assigned this Jun 25, 2026

Noarkhh added this to Smackore Jun 25, 2026

Noarkhh moved this to In Progress in Smackore Jun 25, 2026

Noarkhh changed the title ~~wrap VKVideo elements with ensure_loaded?~~ Rework defining output stream formats Jun 25, 2026

Fix credo

5b20a5c

Noarkhh force-pushed the transcoder-api-rework branch from d976cf3 to 5b20a5c Compare June 26, 2026 13:28

Add and use OutputFormat structs

f8ad893

Noarkhh requested review from FelonEkonom and varsill June 29, 2026 16:08

Noarkhh moved this from In Progress to In Review in Smackore Jun 29, 2026

FelonEkonom reviewed Jun 30, 2026

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Noarkhh requested a review from FelonEkonom July 1, 2026 09:10

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Noarkhh requested a review from FelonEkonom July 1, 2026 09:42

FelonEkonom approved these changes Jul 1, 2026

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varsill requested changes Jul 1, 2026

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Change state to a struct

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Noarkhh requested a review from varsill July 1, 2026 13:25

FelonEkonom self-requested a review July 1, 2026 13:49

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Update examples

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Noarkhh requested a review from FelonEkonom July 2, 2026 07:36

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Comment thread lib/transcoder/audio.ex Outdated

Comment thread lib/transcoder/audio.ex Outdated

Comment thread lib/transcoder/audio.ex Outdated

Comment thread lib/transcoder/output_format.ex

Noarkhh requested a review from varsill July 6, 2026 13:55

Noarkhh requested a review from FelonEkonom July 6, 2026 13:55

Add explicit raises about input formats

9388e94

varsill approved these changes Jul 7, 2026

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Improve resampling

7c2aa8e

khamilowicz mentioned this pull request Jul 15, 2026

Tutorial part 2 membraneframework-labs/ex_broadcaster#4

Open

Noarkhh added 2 commits July 15, 2026 20:03

Merge branch 'master' into transcoder-api-rework

d583fb6

Minor refactor

52ed82c

FelonEkonom reviewed Jul 16, 2026

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Noarkhh added 3 commits July 22, 2026 17:40

Rework video transcoding

3abf6f0

Minor refactor

c5f363c

Fixes

b295c5d

Noarkhh force-pushed the transcoder-api-rework branch from c0ebaa7 to b295c5d Compare July 27, 2026 10:19

Smaller fixes

2b791dd

Noarkhh requested a review from varsill July 27, 2026 12:04

varsill requested changes Jul 27, 2026

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Noarkhh added 2 commits July 27, 2026 16:39

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0cc0e25

Don't transcode when resolution doesnt change

1e457bd

Noarkhh requested a review from varsill July 28, 2026 09:19

	Struct defining the desired output Membrane stream format.
	Struct defining the desired output MPEGAudio stream format.

		@@ -259,18 +300,40 @@ defmodule Membrane.Transcoder do

		spec = child(funnel_name, Funnel) \|> bin_output(pad_ref)

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Noarkhh commented Jun 25, 2026 •

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