[FFmpeg-devel] [PATCH 1/3] avformat/mp3dec: only call ffio_ensure_seekback once

[FFmpeg-devel] [PATCH 1/3] avformat/mp3dec: only call ffio_ensure_seekback once

[Marton Balint]

Otherwise the subsequent ffio_ensure_seekback calls destroy the buffer of the
earlier. The worst case ~66kB seekback is so small it is easier to request it
entirely.

Fixes ticket #10837, a regression since
0d17f5228f4d3854066ec1001f69c7d1714b0df9.

Signed-off-by: Marton Balint <cus@passwd.hu>
---
 libavformat/mp3dec.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
index ec6cf567bc..78d6c8c71c 100644
--- a/libavformat/mp3dec.c
+++ b/libavformat/mp3dec.c
@@ -32,6 +32,7 @@
 #include "replaygain.h"
 
 #include "libavcodec/codec_id.h"
+#include "libavcodec/mpegaudio.h"
 #include "libavcodec/mpegaudiodecheader.h"
 
 #define XING_FLAG_FRAMES 0x01
@@ -400,15 +401,16 @@ static int mp3_read_header(AVFormatContext *s)
     if (ret < 0)
         return ret;
 
+    ret = ffio_ensure_seekback(s->pb, 64 * 1024 + MPA_MAX_CODED_FRAME_SIZE + 4);
+    if (ret < 0)
+        return ret;
+
     off = avio_tell(s->pb);
     for (i = 0; i < 64 * 1024; i++) {
         uint32_t header, header2;
         int frame_size;
-        if (!(i&1023))
-            ffio_ensure_seekback(s->pb, i + 1024 + 4);
         frame_size = check(s->pb, off + i, &header);
         if (frame_size > 0) {
-            ffio_ensure_seekback(s->pb, i + 1024 + frame_size + 4);
             ret = check(s->pb, off + i + frame_size, &header2);
             if (ret >= 0 &&
                 (header & MP3_MASK) == (header2 & MP3_MASK))
-- 
2.35.3

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[FFmpeg-devel] [PATCH 2/3] avformat/mp3dec: simplify inner frame size check in mp3_read_header

[Marton Balint]

We are protecting the checked buffer with ffio_ensure_seekback(), so if the
inner check fails with a seek error, that likely means the end of file was
reached when checking for the next frame. This could also be the result of a
wrongly guessed (larger than normal) frame size, so let's continue the loop
instead of breaking out early. It will end sooner or later anyway.

Signed-off-by: Marton Balint <cus@passwd.hu>
---
 libavformat/mp3dec.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
index 78d6c8c71c..4abc73966f 100644
--- a/libavformat/mp3dec.c
+++ b/libavformat/mp3dec.c
@@ -412,14 +412,8 @@ static int mp3_read_header(AVFormatContext *s)
         frame_size = check(s->pb, off + i, &header);
         if (frame_size > 0) {
             ret = check(s->pb, off + i + frame_size, &header2);
-            if (ret >= 0 &&
-                (header & MP3_MASK) == (header2 & MP3_MASK))
-            {
+            if (ret >= 0 && (header & MP3_MASK) == (header2 & MP3_MASK))
                 break;
-            } else if (ret == CHECK_SEEK_FAILED) {
-                av_log(s, AV_LOG_ERROR, "Invalid frame size (%d): Could not seek to %"PRId64".\n", frame_size, off + i + frame_size);
-                return AVERROR(EINVAL);
-            }
         } else if (frame_size == CHECK_SEEK_FAILED) {
             av_log(s, AV_LOG_ERROR, "Failed to read frame size: Could not seek to %"PRId64".\n", (int64_t) (i + 1024 + frame_size + 4));
             return AVERROR(EINVAL);
-- 
2.35.3

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[FFmpeg-devel] [PATCH 3/3] avformat/mp3dec: change bogus error message if read_header encounters EOF

[Marton Balint]

Because of ffio_ensure_seekback() a seek error normally should only happen if
the end of file is reached during checking for the junk run-in. Also use proper
error code.

Signed-off-by: Marton Balint <cus@passwd.hu>
---
 libavformat/mp3dec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
index 4abc73966f..f421e03926 100644
--- a/libavformat/mp3dec.c
+++ b/libavformat/mp3dec.c
@@ -415,8 +415,8 @@ static int mp3_read_header(AVFormatContext *s)
             if (ret >= 0 && (header & MP3_MASK) == (header2 & MP3_MASK))
                 break;
         } else if (frame_size == CHECK_SEEK_FAILED) {
-            av_log(s, AV_LOG_ERROR, "Failed to read frame size: Could not seek to %"PRId64".\n", (int64_t) (i + 1024 + frame_size + 4));
-            return AVERROR(EINVAL);
+            av_log(s, AV_LOG_ERROR, "Failed to find two consecutive MPEG audio frames.\n");
+            return AVERROR_INVALIDDATA;
         }
     }
     if (i == 64 * 1024) {
-- 
2.35.3

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Re: [FFmpeg-devel] [PATCH 1/3] avformat/mp3dec: only call ffio_ensure_seekback once

[Marton Balint]

On Tue, 14 May 2024, Marton Balint wrote:

> Otherwise the subsequent ffio_ensure_seekback calls destroy the buffer of the
> earlier. The worst case ~66kB seekback is so small it is easier to request it
> entirely.
>
> Fixes ticket #10837, a regression since
> 0d17f5228f4d3854066ec1001f69c7d1714b0df9.

Will apply the series in 1-2 days.

Regards,
Marton

>
> Signed-off-by: Marton Balint <cus@passwd.hu>
> ---
> libavformat/mp3dec.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
> index ec6cf567bc..78d6c8c71c 100644
> --- a/libavformat/mp3dec.c
> +++ b/libavformat/mp3dec.c
> @@ -32,6 +32,7 @@
> #include "replaygain.h"
>
> #include "libavcodec/codec_id.h"
> +#include "libavcodec/mpegaudio.h"
> #include "libavcodec/mpegaudiodecheader.h"
>
> #define XING_FLAG_FRAMES 0x01
> @@ -400,15 +401,16 @@ static int mp3_read_header(AVFormatContext *s)
>     if (ret < 0)
>         return ret;
>
> +    ret = ffio_ensure_seekback(s->pb, 64 * 1024 + MPA_MAX_CODED_FRAME_SIZE + 4);
> +    if (ret < 0)
> +        return ret;
> +
>     off = avio_tell(s->pb);
>     for (i = 0; i < 64 * 1024; i++) {
>         uint32_t header, header2;
>         int frame_size;
> -        if (!(i&1023))
> -            ffio_ensure_seekback(s->pb, i + 1024 + 4);
>         frame_size = check(s->pb, off + i, &header);
>         if (frame_size > 0) {
> -            ffio_ensure_seekback(s->pb, i + 1024 + frame_size + 4);
>             ret = check(s->pb, off + i + frame_size, &header2);
>             if (ret >= 0 &&
>                 (header & MP3_MASK) == (header2 & MP3_MASK))
> -- 
> 2.35.3
>
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
>
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