[FFmpeg-devel] [PATCH] avformat/libopenmpt: implement file reading callbacks (PR #20801)

[paper via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20801 opened by paper
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20801
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20801.patch

Before, this code would unnecessarily waste quite a bit of memory
reading the entire file in, and in many cases just freeing the
result and throwing it out anyway.

This commit changes the behavior to use libopenmpt's callback
structure. This is much more memory efficient, especially for
particularly large files.

Both pre-0.3.0 and post-0.3.0 preprocessor branches have been
tested working with a plain amiga-style 'M.K.' module in ffplay.

Signed-off-by: Paper <paper@tflc.us>


>From 81787bbaa31733ad7c5dd2ea727bc7bd06104719 Mon Sep 17 00:00:00 2001
From: Paper <paper@tflc.us>
Date: Tue, 2 Sep 2025 10:34:14 -0400
Subject: [PATCH] avformat/libopenmpt: implement file reading callbacks

Before, this code would unnecessarily waste quite a bit of memory
reading the entire file in, and in many cases just freeing the
result and throwing it out anyway.

This commit changes the behavior to use libopenmpt's callback
structure. This is much more memory efficient, especially for
particularly large files.

Both pre-0.3.0 and post-0.3.0 preprocessor branches have been
tested working with a plain amiga-style 'M.K.' module in ffplay.

Signed-off-by: Paper <paper@tflc.us>
---
 libavformat/libopenmpt.c | 66 ++++++++++++++++++++++++++++------------
 1 file changed, 47 insertions(+), 19 deletions(-)

diff --git a/libavformat/libopenmpt.c b/libavformat/libopenmpt.c
index 46af4bff22..52f4ab2b7d 100644
--- a/libavformat/libopenmpt.c
+++ b/libavformat/libopenmpt.c
@@ -69,6 +69,51 @@ static void openmpt_logfunc(const char *message, void *userdata)
     av_log(userdata, level, "%s\n", message);
 }
 
+static size_t av_openmpt_read(void *stream, void *dst, size_t bytes)
+{
+    AVIOContext *ioctx = stream;
+    int r;
+
+    /* avio_read takes an int, cap the size accordingly */
+    if (bytes > (size_t)INT_MAX)
+        bytes = (size_t)INT_MAX;
+
+    r = avio_read(ioctx, dst, bytes);
+
+    return (r >= 0) ? r : 0;
+}
+
+static int av_openmpt_seek(void *stream, int64_t offset, int whence)
+{
+    AVIOContext *ioctx = stream;
+    int whence_av;
+
+    switch (whence) {
+    case OPENMPT_STREAM_SEEK_SET: whence_av = SEEK_SET; break;
+    case OPENMPT_STREAM_SEEK_CUR: whence_av = SEEK_CUR; break;
+    case OPENMPT_STREAM_SEEK_END: whence_av = SEEK_END; break;
+    /* invalid value, punt */
+    default: return -1;
+    }
+
+    /* openmpt expects stdio-style seek; don't return new position */
+    return (avio_seek(ioctx, offset, whence_av) < 0) ? -1 : 0;
+}
+
+static int64_t av_openmpt_tell(void *stream)
+{
+    AVIOContext *ioctx = stream;
+    int64_t r = avio_tell(ioctx);
+
+    return (r < 0) ? -1 : r;
+}
+
+static const openmpt_stream_callbacks openmpt_cbs = {
+    av_openmpt_read,
+    av_openmpt_seek,
+    av_openmpt_tell
+};
+
 #define add_meta(s, name, meta)                    \
 do {                                               \
     const char *value = meta;                      \
@@ -81,30 +126,14 @@ static int read_header_openmpt(AVFormatContext *s)
 {
     AVStream *st;
     OpenMPTContext *openmpt = s->priv_data;
-    int64_t size;
-    char *buf;
 #if OPENMPT_API_VERSION_AT_LEAST(0,3,0)
     int error;
 #endif
     int ret;
 
-    size = avio_size(s->pb);
-    if (size <= 0)
-        return AVERROR_INVALIDDATA;
-    buf = av_malloc(size);
-    if (!buf)
-        return AVERROR(ENOMEM);
-    size = avio_read(s->pb, buf, size);
-    if (size < 0) {
-        av_log(s, AV_LOG_ERROR, "Reading input buffer failed.\n");
-        av_freep(&buf);
-        return size;
-    }
-
 #if OPENMPT_API_VERSION_AT_LEAST(0,3,0)
     error = OPENMPT_ERROR_OK;
-    openmpt->module = openmpt_module_create_from_memory2(buf, size, openmpt_logfunc, s, NULL, NULL, &error, NULL, NULL);
-    av_freep(&buf);
+    openmpt->module = openmpt_module_create2(openmpt_cbs, s->pb, openmpt_logfunc, s, NULL, NULL, &error, NULL, NULL);
     if (!openmpt->module) {
         if (error == OPENMPT_ERROR_OUT_OF_MEMORY)
             return AVERROR(ENOMEM);
@@ -114,8 +143,7 @@ static int read_header_openmpt(AVFormatContext *s)
             return AVERROR_UNKNOWN;
     }
 #else
-    openmpt->module = openmpt_module_create_from_memory(buf, size, openmpt_logfunc, s, NULL);
-    av_freep(&buf);
+    openmpt->module = openmpt_module_create(openmpt_cbs, s->pb, openmpt_logfunc, s, NULL);
     if (!openmpt->module)
             return AVERROR_INVALIDDATA;
 #endif
-- 
2.49.1

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