Change default audio format to float32 (#1284)

[ddennedy]

ddennedy@pop-os:~/Downloads$ sh audio_null_test.sh

== 1. transparency: no filters, float in, float out ==
default flags:
  PASS  residual -inf dBFS (bit-exact)
mlt_audio_format=f32le:
  PASS  residual -inf dBFS (bit-exact)

== 2. correctness: acompressor vs FFmpeg's own float output ==
reference peak        : 12.589864 dBFS
MLT default peak      : 12.589864 dBFS
MLT f32le peak        : 12.589864 dBFS
default flags:
  PASS  residual -inf dBFS (bit-exact)
mlt_audio_format=f32le:
  PASS  residual -inf dBFS (bit-exact)

== 3. damage: residual written out for listening ==
  ./null-test/residual.wav  peak -inf dBFS
  (normalise it up and play it: this is the distortion the default path adds)

RESULT: all checks passed

[ddennedy]

@bmatherly This also works in Shotcut after one small change for the peak and waveform meters, which assume 16-bit int

diff --git a/src/sharedframe.cpp b/src/sharedframe.cpp
index 1c5255e0..cb5910eb 100644
--- a/src/sharedframe.cpp
+++ b/src/sharedframe.cpp
@@ -253,7 +253,8 @@ int SharedFrame::get_audio_samples() const
 
 const int16_t *SharedFrame::get_audio() const
 {
-    mlt_audio_format format = get_audio_format();
+    // Scope widgets reading through SharedFrame currently consume signed 16-bit PCM.
+    mlt_audio_format format = mlt_audio_s16;
     int frequency = get_audio_frequency();
     int channels = get_audio_channels();
     int samples = get_audio_samples();

[Copilot]

Pull request overview

Changes default and realtime consumer audio paths from S16 to interleaved float32.

Changes:

• Sets the framework default to f32le.
• Updates SDL2 consumers for float32 playback and volume handling.
• Updates RtAudio streams and buffers for float32.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
src/framework/mlt_consumer.c	Changes the default audio format and preserves explicit S16 selection.
src/modules/sdl2/consumer_sdl2.c	Uses float32 audio with SDL2.
src/modules/sdl2/consumer_sdl2_audio.c	Converts audio-only SDL2 playback to float32.
src/modules/rtaudio/consumer_rtaudio.cpp	Converts RtAudio playback to float32.

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[bmatherly]

@bmatherly This also works in Shotcut after one small change for the peak and waveform meters, which assume 16-bit int

Thanks for letting me know. I will come up with a general solution for this in Shotcut.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.