Re: [FFmpeg-devel] [FFmpeg-cvslog] avcodec/mjpegenc: Simplify allocating huffman table

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

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Michael Niedermayer:
> On Wed, Mar 26, 2025 at 04:08:55AM +0000, Andreas Rheinhardt wrote:
>> ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt@outlook.com> | Mon Mar  3 02:36:55 2025 +0100| [24dbc4c2e82481f89d6fcacee1949e5038c5c2fc] | committer: Andreas Rheinhardt
>>
>> avcodec/mjpegenc: Simplify allocating huffman table
>>
>> Reuse the already computed value of macroblocks; use an array
>> instead of a switch, evaluate 64 * sizeof(MJpegHuffmanCode)
>> at compile-time.
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>>
>>> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=24dbc4c2e82481f89d6fcacee1949e5038c5c2fc
>> ---
>>
>>  libavcodec/mjpegenc.c | 24 ++++++++++--------------
>>  1 file changed, 10 insertions(+), 14 deletions(-)
> 
> Breaks: (did not investigate why)
> 
> ./ffmpeg  -i lena.pnm -strict -1 -s 4096x2048 -bitexact -y /tmp/file-4096x2048.m2v && ./ffmpeg -i /tmp/file-4096x2048.m2v -y -bitexact /tmp/file-4096x2048-dec.jpg
> 
> [vost#0:0/mjpeg @ 0x5576d6b7ab00] [enc:mjpeg @ 0x5576d6b79580] Error while opening encoder - maybe incorrect parameters such as bit_rate, rate, width or height.
> [vf#0:0 @ 0x5576d6b7f140] Error sending frames to consumers: Cannot allocate memory
> [vf#0:0 @ 0x5576d6b7f140] Task finished with error code: -12 (Cannot allocate memory)
> [vf#0:0 @ 0x5576d6b7f140] Terminating thread with return code -12 (Cannot allocate memory)
> [vost#0:0/mjpeg @ 0x5576d6b7ab00] [enc:mjpeg @ 0x5576d6b79580] Could not open encoder before EOF
> [vost#0:0/mjpeg @ 0x5576d6b7ab00] Task finished with error code: -22 (Invalid argument)
> [vost#0:0/mjpeg @ 0x5576d6b7ab00] Terminating thread with return code -22 (Invalid argument)
> [out#0/image2 @ 0x5576d6b7ec80] Nothing was written into output file, because at least one of its streams received no packets.
> 

Patch attached. Thanks for testing.

- Andreas

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From 11d68061103257173a3c065b176cc84ad63885a7 Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Thu, 27 Mar 2025 03:03:02 +0100
Subject: [PATCH] avcodec/mjpegenc: Don't allocate unnecessarily much memory

We need to allocate space for 64 coefficients per block;
24dbc4c2e82481f89d6fcacee1949e5038c5c2fc wanted to
perform the calculation 64*sizeof(MJpegHuffmanCode)
at compile time, yet in the end did it in a way that
made it allocate 64 times as much memory as needed.

Reported-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/mjpegenc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/libavcodec/mjpegenc.c b/libavcodec/mjpegenc.c
index 668065011c..214e2b0ec1 100644
--- a/libavcodec/mjpegenc.c
+++ b/libavcodec/mjpegenc.c
@@ -291,13 +291,12 @@ static int alloc_huffman(MJPEGEncContext *const m2)
     static const char blocks_per_mb[] = {
         [CHROMA_420] = 6, [CHROMA_422] = 8, [CHROMA_444] = 12
     };
-    size_t num_blocks, num_codes;
+    size_t num_blocks;
 
     // Make sure we have enough space to hold this frame.
     num_blocks = s->c.mb_num * blocks_per_mb[s->c.chroma_format];
-    num_codes = num_blocks * 64;
 
-    m->huff_buffer = av_malloc_array(num_codes,
+    m->huff_buffer = av_malloc_array(num_blocks,
                                      64 /* codes per MB */ * sizeof(MJpegHuffmanCode));
     if (!m->huff_buffer)
         return AVERROR(ENOMEM);
-- 
2.45.2


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