demux_lavf: workaround reading gif from unseekable streams

FFmpeg, being the pile of trash as usual, recently broke this. Add our
own trash hack to trashily workaround this shit.

Fixes: #7893

1 files changed, 19 insertions, 0 deletions

diff --git a/demux/demux_lavf.c b/demux/demux_lavf.c
index 50b9e044e4..e3ebcbfdc6 100644
--- a/demux/demux_lavf.c
+++ b/demux/demux_lavf.c
@@ -148,6 +148,7 @@ struct format_hack {
     bool no_seek : 1;
     bool no_pcm_seek : 1;
     bool no_seek_on_no_duration : 1;
+    bool readall_on_no_streamseek : 1;
 };
 
 #define BLACKLIST(fmt) {fmt, .ignore = true}
@@ -186,6 +187,10 @@ static const struct format_hack format_hacks[] = {
     // reset timestamps, which causes all sorts of problems.
     {"ogg", .linearize_audio_ts = true, .use_stream_ids = true},
 
+    // At some point, FFmpeg lost the ability to read gif from unseekable
+    // streams.
+    {"gif", .readall_on_no_streamseek = true},
+
     TEXTSUB("aqtitle"), TEXTSUB("jacosub"), TEXTSUB("microdvd"),
     TEXTSUB("mpl2"), TEXTSUB("mpsub"), TEXTSUB("pjs"), TEXTSUB("realtext"),
     TEXTSUB("sami"), TEXTSUB("srt"), TEXTSUB("stl"), TEXTSUB("subviewer"),
@@ -1020,6 +1025,20 @@ static int demux_open_lavf(demuxer_t *demuxer, enum demux_check check)
         return -1;
     }
 
+    if (priv->format_hack.readall_on_no_streamseek && priv->pb &&
+        !priv->pb->seekable)
+    {
+        MP_VERBOSE(demuxer, "Non-seekable demuxer pre-read hack...\n");
+        // Read incremental to avoid unnecessary large buffer sizes.
+        int r = 0;
+        for (int n = 16; n < 29; n++) {
+            r = stream_peek(priv->stream, 1 << n);
+            if (r < (1 << n))
+                break;
+        }
+        MP_VERBOSE(demuxer, "...did read %d bytes.\n", r);
+    }
+
     if (avformat_open_input(&avfc, priv->filename, priv->avif, &dopts) < 0) {
         MP_ERR(demuxer, "avformat_open_input() failed\n");
         av_dict_free(&dopts);