#1402: import MP1 (A_MPEG/L1) audio from Matroska
Problem: the Matroska demuxer mapped A_MPEG/L2 and A_MPEG/L3 only, so a Layer I track was reported as an unsupported codec even though the MP1/MP2 decoder (#809) reads Layer I. Fix: add Codec::Mp1 for A_MPEG/L1 and route it through the same packet duration and decoder path as Mp2. Test remuxes synthetic Layer I frames into Matroska with ffmpeg and compares our decode (max error 3e-5). Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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vangel76andClaude Sonnet 5.5 committed
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@@ -83,7 +83,7 @@ fn audio_starts(file: &MkvFile, bytes: &crate::Src, ti: usize, rate: i64) -> Vec
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let out_rate = u32::try_from(rate).unwrap_or(0);
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let frame = match &t.codec {
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Codec::Aac { asc } => fixed_packet_samples(FixedFrames::Aac(asc), &[], out_rate),
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Codec::Mp3 | Codec::Mp2 => fixed_packet_samples(FixedFrames::MpegAudio, &first(), out_rate),
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Codec::Mp3 | Codec::Mp2 | Codec::Mp1 => fixed_packet_samples(FixedFrames::MpegAudio, &first(), out_rate),
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Codec::Ac3 => fixed_packet_samples(FixedFrames::Ac3, &first(), out_rate),
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Codec::Eac3 => fixed_packet_samples(FixedFrames::Eac3, &first(), out_rate),
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_ => None,
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@@ -317,7 +317,7 @@ fn codec_label(c: &Codec) -> String {
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Codec::Flac { .. } => "FLAC".into(),
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Codec::Pcm { bits, float, .. } => format!("PCM {bits}-bit{}", if *float { " float" } else { "" }),
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Codec::Mp3 => "MP3".into(),
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Codec::Mp2 => "MPEG Audio".into(),
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Codec::Mp2 | Codec::Mp1 => "MPEG Audio".into(),
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Codec::Other(id) if id == "V_MPEG2" => "MPEG-2 Video".into(),
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Codec::Other(id) if id == "V_MPEG1" => "MPEG-1 Video".into(),
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other => other.name().to_string(),
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@@ -486,6 +486,7 @@ impl MkvSource {
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Codec::Opus { head } => PacketDecoder::opus(filmcraft_opus::OpusHead::parse(head).map_err(|e| CodecError::Unsupported(format!("Opus: {e}")))?),
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Codec::Mp3 => PacketDecoder::new(CODEC_TYPE_MP3, rate, None),
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Codec::Mp2 => PacketDecoder::mpeg_audio(2, rate),
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Codec::Mp1 => PacketDecoder::mpeg_audio(1, rate),
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Codec::Ac3 | Codec::Eac3 => PacketDecoder::ac3(),
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// symphonia wants the STREAMINFO block body: skip `fLaC` + the 4-byte block header.
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Codec::Flac { private } => PacketDecoder::new(CODEC_TYPE_FLAC, rate, private.get(8..42).map(<[u8]>::to_vec)),
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@@ -0,0 +1,89 @@
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//! MPEG audio Layer I (MP1) in Matroska (`A_MPEG/L1`, #1402) against ffmpeg's decode. No
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//! installed encoder writes Layer I, so the frames are synthetic (valid random Layer I frames,
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//! as in `crates/mpa/tests/oracle.rs`) and ffmpeg only remuxes them into Matroska and decodes.
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mod common;
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use common::*;
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struct Bits(Vec<u8>, usize);
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impl Bits {
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fn put(&mut self, v: u32, n: u32) {
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for i in (0..n).rev() {
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if self.1.is_multiple_of(8) {
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self.0.push(0);
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}
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if (v >> i) & 1 == 1 {
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let last = self.0.len() - 1;
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self.0[last] |= 0x80 >> (self.1 % 8);
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}
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self.1 += 1;
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}
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}
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}
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/// Mono Layer I frames, MPEG-1, 48 kHz, 192 kbit/s (192-byte frames): allocations on the first 8
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/// subbands only, so every frame fits.
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fn layer1_stream(frames: usize) -> Vec<u8> {
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let mut seed = 0x2545_F491u32;
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let mut rnd = |n: u32| {
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seed ^= seed << 13;
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seed ^= seed >> 17;
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seed ^= seed << 5;
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seed % n
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};
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let mut out = Vec::new();
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for _ in 0..frames {
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let mut b = Bits(Vec::new(), 0);
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for byte in [0xFFu32, 0xFF, 6 << 4 | 1 << 2, 3 << 6] {
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b.put(byte, 8);
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}
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let alloc: Vec<u32> = (0..32).map(|sb| if sb < 8 { 1 + rnd(8) } else { 0 }).collect();
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for &a in &alloc {
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b.put(a, 4);
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}
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for &a in &alloc {
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if a != 0 {
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b.put(10 + rnd(30), 6);
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}
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}
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for _ in 0..12 {
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for &a in &alloc {
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if a != 0 {
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b.put(rnd((1 << (a + 1)) - 1), a + 1);
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}
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}
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}
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let mut f = b.0;
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f.resize(192, 0);
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out.extend(f);
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}
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out
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}
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#[test]
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fn mp1_in_matroska_matches_ffmpeg() {
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let ff = filmcraft_testkit::require_ffmpeg!();
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let raw = dir().join("synthetic_layer1.mp1");
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std::fs::create_dir_all(dir()).unwrap();
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std::fs::write(&raw, layer1_stream(250)).unwrap();
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let Some(mkv) = fixture(&ff, "synthetic_layer1.mkv", &["-f", "mp3", "-i", raw.to_str().unwrap(), "-c:a", "copy"]) else {
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eprintln!("SKIPPED: this ffmpeg can't remux Layer I into Matroska");
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return;
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};
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let m = filmcraft_matroska::open(bytes(&mkv)).unwrap();
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assert!(matches!(m.tracks.first().map(|t| &t.codec), Some(filmcraft_matroska::Codec::Mp1)), "A_MPEG/L1 maps to Codec::Mp1");
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let src = filmcraft_codecs::open_bytes("synthetic_layer1.mkv", bytes(&mkv)).unwrap();
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let a = src.info().audio().cloned().unwrap();
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assert_eq!((a.sample_rate, a.channels), (48_000, 1));
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let want = ffmpeg_audio_f32(&ff, &mkv, &[]);
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let n = want.len().min(250 * 384) - 800;
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let got = src.audio(0, n, 48_000).unwrap();
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let peak = want.iter().fold(0f32, |m, x| m.max(x.abs()));
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// ffmpeg's CLI may or may not drop the decoder delay of a stream copy; search a few lags
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let (worst, lag) = (-2i64..=2)
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.map(|lag| ((2..n - 2).map(|i| (want[(i as i64 + lag) as usize] - got.channels[0][i]).abs()).fold(0f32, f32::max), lag))
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.fold((f32::INFINITY, 0), |m, x| if x.0 < m.0 { x } else { m });
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println!("mkv Layer I: max error {worst} at lag {lag}, peak {peak}");
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assert!(peak > 0.01 && worst <= 2e-4, "peak {peak}, max error {worst} at lag {lag}");
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}
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@@ -73,7 +73,7 @@ while let Some(p) = d.next_packet()? { // file order, all tracks
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| `A_VORBIS` | `Vorbis` | three headers split from Xiph-laced CodecPrivate |
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| `A_FLAC` | `Flac` | `fLaC` + metadata blocks |
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| `A_PCM/INT/LIT`, `A_PCM/INT/BIG`, `A_PCM/FLOAT/IEEE` | `Pcm` | bit depth from Audio |
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| `A_AC3`, `A_EAC3`, `A_MPEG/L3`, `A_MPEG/L2` | `Ac3`, `Eac3`, `Mp3`, `Mp2` | |
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| `A_AC3`, `A_EAC3`, `A_MPEG/L3`, `A_MPEG/L2`, `A_MPEG/L1` | `Ac3`, `Eac3`, `Mp3`, `Mp2`, `Mp1` | |
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| `S_TEXT/UTF8` | `SubRip` | |
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| `S_TEXT/WEBVTT`, `D_WEBVTT/*` (WebM) | `WebVtt` | WebM blocks keep `id\nsettings\npayload` |
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| `S_TEXT/ASS`, `S_TEXT/SSA` | `Ass` | script header |
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@@ -45,6 +45,8 @@ pub enum Codec {
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Mp3,
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/// `A_MPEG/L2`.
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Mp2,
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/// `A_MPEG/L1`.
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Mp1,
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/// `S_TEXT/UTF8` (SubRip-style plain text).
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SubRip,
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/// `S_TEXT/WEBVTT`, or WebM's `D_WEBVTT/{SUBTITLES,CAPTIONS,DESCRIPTIONS,METADATA}`.
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@@ -86,6 +88,7 @@ impl Codec {
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Codec::Eac3 => "eac3".into(),
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Codec::Mp3 => "mp3".into(),
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Codec::Mp2 => "mp2".into(),
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Codec::Mp1 => "mp1".into(),
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Codec::SubRip => "subrip".into(),
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Codec::WebVtt => "webvtt".into(),
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Codec::Ass { ssa, .. } => if *ssa { "ssa" } else { "ass" }.into(),
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@@ -173,6 +176,7 @@ pub(crate) fn map_codec(id: &str, private: &[u8], audio: Option<&crate::AudioInf
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"A_EAC3" => Codec::Eac3,
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"A_MPEG/L3" => Codec::Mp3,
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"A_MPEG/L2" => Codec::Mp2,
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"A_MPEG/L1" => Codec::Mp1,
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"S_TEXT/UTF8" => Codec::SubRip,
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"S_TEXT/WEBVTT" | "D_WEBVTT/SUBTITLES" | "D_WEBVTT/CAPTIONS" | "D_WEBVTT/DESCRIPTIONS" | "D_WEBVTT/METADATA" => Codec::WebVtt,
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"S_TEXT/ASS" | "S_ASS" => Codec::Ass { header: p, ssa: false },
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+3
-2
@@ -178,12 +178,12 @@ platforms** G4, G9, G17; **performance** G16; **ecosystem** G11; **measurement**
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- **Have:** E-AC-3 (Dolby Digital Plus) in MP4, MOV, Matroska and MPEG-TS (#647): independent
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substream, 1–6 blocks per syncframe, spectral extension. MP1 / MP2 (MPEG audio Layer I / II):
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own decoder (#809) in raw files, MP4 and MOV (#800), MPEG-TS / PS and Matroska, including the
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own decoder (#809) in raw files, MP4 and MOV (#800), MPEG-TS / PS and Matroska (`A_MPEG/L1` and `L2`, #1402), including the
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bit rate / mode combinations ISO/IEC 11172-3 disallows but ffmpeg writes (its mono default is
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384 kbit/s). OpenEXR stills and image
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sequences (#828): scan-line, uncompressed / RLE / ZIPS / ZIP, half / float / uint, RGB(A) or
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luminance, decoded to linear float frames and bit-exact against ffmpeg.
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- **Missing:** free-format MPEG audio, MP1 in Matroska (`A_MPEG/L1`), E-AC-3 adaptive hybrid
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- **Missing:** free-format MPEG audio, E-AC-3 adaptive hybrid
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transform, enhanced coupling and the extra channels of 7.1 dependent substreams (played as the
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5.1 core), AVI (#598; listed as an extension but no
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demuxer), WMV / ASF, DV / DVCPRO / DV100, MPEG-4 Part 2, FLAC in MP4 (#603), camera RAW (R3D
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@@ -306,3 +306,4 @@ platforms** G4, G9, G17; **performance** G16; **ecosystem** G11; **measurement**
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| Date | Change | Summary |
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|---|---|---|
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| 2026-10-10 | major | Created from ROADMAP.md's "Where we are lacking" (2026-10-05); re-ranked against Premiere 26.5.2 and the 188 open issues; added `.prproj`, 10-bit / 4:2:2 camera decode, launch crashes and missing PR CI, localization, delivery formats |
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| 2026-10-12 | minor | G10: MP1 (`A_MPEG/L1`) in Matroska imports (#1402) |
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